Xanthomonas

Microbiol Res, 2004, 159(4), 425 - 37
In silico analysis of nonribosomal peptide synthetases of Xanthomonas axonopodis pv . citri: identification of putative siderophore and lipopeptide biosynthetic genes; Etchegaray A et al.; The genomes of the plant pathogens Xanthomonas axonopodis (Xac) and Xanthomonas campestris (Xcc) were analysed with the aim of deducing their ability to produce nonribosomal peptides . Nonribosomal peptide synthetase (NRPS) genes were identified in two separate loci of Xac . While the genes of locus 1 are common to both strains, locus 2 was only found in Xac . Dissection and phylogenetic analysis of the condensation and thioesterase domains of the NRPSs of loci 1 and 2 of Xac revealed homology, respectively, with siderophore and lipopeptide synthetases . Further analysis of locus 1 revealed genes related to polyketide and polyamine biosynthesis that could be involved in the assembly of substrates for siderophore biosynthesis in both strains . In vitro production of siderophores by both Xac and Xcc was confirmed . Since bacterial siderophores and lipopeptides can be pathogenic and are typically produced nonribosomally, these results suggest that the identified genes could be involved in phytotoxin production.

Microbiol Res, 2004, 159(4), 419 - 23
Sensitive and specific detection of Xanthomonas campestris pv campestris by PCR using species-specific primers based on hrpF gene sequences; Park YJ et al.; A sensitive and specific assay was developed to detect bacterial black rot of crucifers caused by Xanthomonas campestris pv . campestris (X . c . pv . campestris), in cabbage seed and plant . Primers XCF and XCR from hrpF homologous to nolX, host recognition protein, were used to amplify a 525 bp DNA fragment . PCR technique was applied to detect the pathogen in naturally infected seed and plant of cabbage . The PCR product was only produced from X . c . pv . campestris among 40 isolates of Xanthomonas strains, Escherichia coli (O157:H7), Pectobacterium carotovorum subsp . carotovorum, and other reference bacteria.

Res Microbiol, 2005 Jan-Feb, 156(1), 30 - 4
Protection of Xanthomonas against arsenic toxicity involves the peroxide-sensing transcription regulator OxyR; Sukchawalit R et al.; Arsenic has been shown to mediate its toxicity through induced generation of reactive oxygen species . Here, we examined the role of oxidative stress-inducible genes (katA, ahpC and ohr) and their regulators (oxyR and ohrR) in the response to arsenic treatment in a plant pathogenic bacterium, Xanthomonas campestris pv . phaseoli (Xp) . Overproduction of peroxide-scavenging enzymes (KatA, AhpCF and Ohr) did not enhance arsenic tolerance in wild-type Xp . Furthermore, inactivation of katA, ahpC, ohr, and ohrR genes had no effect on the level of arsenic resistance . By contrast, an oxyR mutant (Xp oxyR) showed increased sensitivity to both pentavalent arsenate and, to a greater extent, trivalent arsenite . The resistance of cells to arsenite treatment was significantly affected by the level of iron . Cells were 10-fold more sensitive to arsenite killing in the presence of excess iron, while removal of iron by an iron chelator (2,2'-dipyridyl) protected Xanthomonas from arsenite toxicity . The arsenite-sensitive phenotype of Xp oxyR could be complemented by the expression of functional OxyR from a plasmid vector, but not by the expression of other known OxyR-regulated peroxide-scavenging enzymes such as KatA and AhpCF, Ohr and OhrR . The data suggested that as yet unidentified, OxyR-regulated gene(s) are involved in conferring arsenic resistance in Xp . To our knowledge, this is the first report showing that the peroxide-sensing regulator OxyR is involved in arsenic resistance.

Protein J, 2004 Oct, 23(7), 437 - 44
Purification and characterization of a lectin from Crotalaria paulina seeds; Pando LA et al.; A lectin was purified from Crotalaria paulina seeds by ion-exchange and FPLC molecular exclusion chromatography . CrpL had an apparent molecular mass of 30 kDa, as determined by SDS-PAGE under non-reducing and reducing conditions . CrpL effectively agglutinated human and cow erythrocytes, and this activity was not affected by 20 mM EDTA, showing no dependence of divalent cations . Hemagglutination was inhibited by N-acetyl-D-galactosamine, D-galactose and was also inhibited by glycoproteins, fetuin and asialofetuin . The N-terminal amino acid sequence of CrpL was identical to those of other lectins from the genus Crotalaria, and amino acid composition showed high amounts of Asx and Glx, and was rich in Gly, Ala and Ser, as also reported for lectins from other Crotalaria species . CrpL inhibited the growth of Xanthomonas axonopodis pv . phaseoli and Xanthomonas axonopodis pv . passiflorae, suggesting a role of this lectin in the defense of seeds against bacterial infections.

Plant Mol Biol, 2004 Nov, 56(4), 573 - 584
Recent progress in the characterization of molecular determinants in the Xanthomonas axonopodis pv . manihotis-cassava interaction; Verdier V et al.; Cassava bacterial blight, caused by Xanthomonas axonopodis pv . manihotis (Xam), is a widespread disease that affects cassava (Manihot esculenta Crantz) . Studies on the pathogen population structure, pathogen diagnosis, identification and expression of plant genes involved in resistance have been carried out . Different molecular techniques were developed to assess the genetic diversity among the Xampopulations . Characterization of Xam population dynamics over time had enable us to determine the different factors that are associated with resistance breakdown and those that influence the genetic structure or virulence phenotypes of the pathogen's population . Methods for detecting the pathogen in vegetative planting materials and true seeds were developed and contributed to reduce the impact of the disease . To better understand the genetics of resistance a quantitative trait loci (QTLs) approach was developed . Using a PCR-based strategy with degenerate primers we isolated two resistance gene candidates in cassava . We also characterized a region of a chromosome rich in R-gene like sequence . In this review we also report the main results obtained by transcript profiling methodologies, cDNA-AFLP and ESTs developed by the authors to characterize the genes involved in disease resistance . All together these techniques allowed the identification of molecular markers either associated to CBB resistance or that may represent putative genes involved in disease resistance . This article reviews current knowledge on the molecular cassava-Xam interactions.

Plant Mol Biol, 2004 Nov, 56(4), 541 - 54
A unigene catalogue of 5700 expressed genes in cassava; Lopez C et al.; Two economically important characters, starch content and cassava bacterial blight resistance, were targeted to generate a large collection of cassava ESTs . Two libraries were constructed from cassava root tissues of varieties with high and low starch contents . Other libraries were constructed from plant tissues challenged by the pathogen Xanthomonas axonopodis pv.manihotis . We report here the single pass sequencing of 11 954 cDNA clones from the 5' ends, including 111 from the 3' ends . Cluster analysis permitted the identification of a unigene set of 5700 sequences . Sequence analyses permitted the assignment of a putative functional category for 37% of sequences whereas ~ 16% sequences did not show any significant similarity with other proteins present in the database and therefore can be considered as cassava specific genes . A group of genes belonging to a large multigene family was identified . We characterize a set of genes detected only in infected libraries putatively involved in the defense response to pathogen infection . By comparing two libraries obtained from cultivars contrasting in their starch content a group of genes associated to starch biosynthesis and differentially expressed was identified . This is the first large cassava EST resource developed today and publicly available thus making a significant contribution to genomic knowledge of cassava.

J Bacteriol, 2005 Jan, 187(2), 649 - 63
The hrpK Operon of Pseudomonas syringae pv . tomato DC3000 Encodes Two Proteins Secreted by the Type III (Hrp) Protein Secretion System: HopB1 and HrpK, a Putative Type III Translocator; Petnicki-Ocwieja T et al.; Pseudomonas syringae is a gram-negative bacterial plant pathogen that is dependent on a type III protein secretion system (TTSS) and the effector proteins it translocates into plant cells for pathogenicity . The P . syringae TTSS is encoded by hrp-hrc genes that reside in a central region of a pathogenicity island (Pai) . Flanking one side of this Pai is the exchangeable effector locus (EEL) . We characterized the transcriptional expression of the open reading frames (ORFs) within the EEL of P . syringae pv . tomato DC3000 . One of these ORFs, PSPTO1406 (hopB1) is expressed in the same transcriptional unit as hrpK . Both HopB1 and HrpK were secreted in culture and translocated into plant cells via the TTSS . However, the translocation of HrpK required its C-terminal half . HrpK shares low similarity with a putative translocator, HrpF, from Xanthomonas campestris pv . vesicatoria . DC3000 mutants lacking HrpK were significantly reduced in disease symptoms and multiplication in planta, whereas DC3000 hopB1 mutants produced phenotypes similar to the wild type . Additionally, hrpK mutants were reduced in their ability to elicit the hypersensitive response (HR), a programmed cell death associated with plant defense . The reduced HR phenotype exhibited by hrpK mutants was complemented by hrpK expressed in bacteria but not by HrpK transgenically expressed in tobacco, suggesting that HrpK does not function inside plant cells . Further experiments identified a C-terminal transmembrane domain within HrpK that is required for HrpK translocation . Taken together, HopB1 is a type III effector and HrpK plays an important role in the TTSS and is a putative type III translocator.

Sci China C Life Sci, 2004 Oct, 47(5), 461 - 9
Genetic diversity of harpins from Xanthomonas oryzae and their activity to induce hypersensitive response and disease resistance in tobacco; Li P et al.; Three hrfA (hypersensitive response-functioning faction A) homologues (hrfl, hrf2 and hrf3) are cloned from 12 strains of Xanthomonas oryzae using PCR based techniques . Hrf1, hrf2 and hrf3 are derived from strains belonging to X . o . pv . oryzae, X . o . pv . oryzicola and X . o . pv . oryzae respectively . Sequence analysis shows that all three genes encode glycine-rich proteins with various numbers of GGG-GG motifs . They all share a conserved cysteine residue at position 45 or 47 . Hrf1 and hrf3 encode Harpin(xoo) while hrf2 encodes Harpin(xooc) Hrf1 and hrf3 encodes two different types of Harpin(xoo) proteins . Hrf1 from X . o . pv . oryzae strains (JxoIII, JxoIV, Jxov, Pxo61, Pxo76, Pxo79, Pxo99, Pxo99 and Pxo124) encodes a 15.6 kD Harpin(xoo) with 3 GGG-GG motifs while Hrf3 from strain Pxo86 and Pxo112 encodes a 15.9 kD Harpin(xoo) with 4 GGG-GG motifs . Harpin(xooc) encoded by hrf2 from X . o . pv . oryzicola (strain RS105) has the molecular weight of 15.3 kD and contains 2 GGG-GG motifs . Cluster analysis is performed using deduced sequences of hrf1, hrf2 and hrf3 as well as previously reported Hpa1 and Xopl protein sequence . The results indicated that Harpin(xoo) and Harpin(xooc) belong to two closely related subgroups . Hrf, hrf2 and hrf3 are expressed in E . coli strain BL21 successfully . Under the same condition, hrf1, hrf2 and hrf3 are expressed at the level of 0.389, 0.530 and 0.083 mg/mL respectively . All expressed hrf1, hrf2 and hrf3 proteins (Harpins) are shown to be able to induce hypersensitive reaction and TMV resistance on tobacco . Among the three proteins, Hrf2 has the highest activity while Hrf3 has the lowest activity.

Proteomics . 2004 Dec 23; {Epub ahead of print}
Comprehensive analysis of the extracellular proteins from Xanthomonas campestris pv . campestris B100; Watt SA et al.; The extracellular proteome of Xanthomonas campestris pv . campestris (Xcc) cultivated in minimal medium was isolated from the cell-free culture supernatant and separated by two-dimensional gel electrophoresis . This technique resolved 97 clearly visible protein spots, which were excised, digested with trypsin and identified on the basis of their peptide mass fingerprints generated by matrix assisted laser desorption/ionisation-time of flight-mass spectrometry . Using this approach 87 different proteins could be distinguished . The Signal P software predicted putative signal peptides for 53% of the extracellular proteins . These proteins are probably transported over the inner membrane and are localized in the periplasm, the outer membrane or secreted into the extracellular space . Among the secreted proteins are 11 degradative enzymes, which are involved in pathogenesis of Xcc . The proteins without obvious secretion signals are known to serve functions in the cytosol . How the cytosolic proteins are delivered to the extracellular space remains unclear.

Syst Appl Microbiol, 2004 Nov, 27(6), 755 - 62
Reclassification of the xanthomonads associated with bacterial spot disease of tomato and pepper; Jones JB et al.; Four phenotypic xanthomonad groups have been identified that are pathogenic to pepper, tomato, or both hosts . These include groups A and C which are found in Xanthomonas axonopodis pv . vesicatoria, group B found in X . vesicatoria, and group D found in 'X . gardneri' . We present DNA:DNA hybridization data in which X . axonopodis pv . vesicatoria group A and C strains have less than 70% DNA relatedness with each other, with the type strain of X . axonopodis, and with the currently classified species within Xanthomonas and, therefore, should be removed from this species and given species status . We present information that the A strains most closely resemble the strains originally isolated by Doidge in 1921 . In an attempt to avoid confusion in nomenclature as stated in Principle 1 of the Bacteriological Code, we propose that the A strains of X . axonopodis pv . vesicatoria be renamed as X . euvesicatoria (ATCC11633T= NCPPB2968T = ICMP 109T = ICMP 98T) . Use of the euvesicatoria epithet should be reserved for strains originally identified by Doidge, which she designated Bacterium vesicatorium (Ann . Appl . Biol . 7: 407-430, 1921) in the original description when she referred to those strains as being feebly amylolytic . The name X . perforans sp . nov . is proposed for the C group of strains previously designated as X . axonopodis pv . vesicatoria (ATCC BAA-983T = NCPPB 4321T) . We also propose that 'X . gardneri', which has less than 70% DNA relatedness with any of the Xanthomonas species and which has never had taxonomic status, be named X . gardneri (ATCC 19865T = NCPPB 881T) to reflect the specific epithet proposed by Sutic in 1957.

Plant Mol Biol, 2004 Aug, 55(6), 883 - 904
CAZFP1, Cys2/His2-type zinc-finger transcription factor gene functions as a pathogen-induced early-defense gene in Capsicum annuum; Kim SH et al.; A pepper zinc-finger protein gene, CAZFP1 , encoding the Cys2/His2-type zinc-finger transcription factor was isolated from pepper leaves inoculated with an avirulent strain Bv5-4a of Xanthomonas campestris pv . vesicatoria . The CAZFP1 protein is a nuclear targeting protein, which functions as a transcriptional regulator . The full-length CAZFP1 had no transcriptional activation activity, whereas the C-terminal region of CAZFP1 had transactivation activity . The CAZFP1 transcripts were constitutively expressed in the pepper stem, root, flower and red fruit, but were not detectable in the leaf and green fruit . The CAZFP1 transcripts accumulated earlier than the CAZFP1 (PR-1) gene in the incompatible interaction of the pepper leaves with X . campestris pv . vesicatoria . The CAZFP1 transcripts were significantly induced in the systemic, uninoculated leaf tissues early after inoculation with bacterial pathogens, but gradually declined thereafter . The CAZFP1 transcripts were localized, and confined to the phloem cells of the vascular bundle in the pepper leaf midrib in response to Colletotrichum . coccodes infection, ethylene and abscisic acid . The CAZFP1 gene was also induced much earlier by abiotic elicitors and environmental stresses, compared with the CAZFP1 gene . Overexpression of the CAZFP1 gene in the transgenic Arabidopsis plants enhanced not only the resistance against infection by Pseudomonas syringae pv . tomato, but also the drought tolerance . These results suggest that the CAZFP1 gene functions as an early-defense gene to enhance disease resistance and drought tolerance.

Zhi Wu Sheng Li Yu Fen Zi Sheng Wu Xue Xue Bao, 2004 Jun, 30(3), 331 - 8
{Physiological and genetic analysis of lesion resembling disease mutants (lrd) of Oryza sativa L.}; Wang JJ et al.; Ten indica rice and eight japonica rice mutants with lesion resembling disease (lrd27-44) were obtained by gamma-ray mutagenesis of the whole genomes . These mutants exhibited diverse lesion mimic phenotypes under different growth environments, could be accordingly classified two types, sensitive and insensitive to environments . Basing on difference in development of lesion mimics, they can be divided into three categories: whole life lesion mimics (WLLM), vegetative initiation lesion mimics (VILM), and reproductive initiation lesion mimics (RILM) . Lesion mimics resulted from the programmed cell death and were triggered by light, but not by wounding . The genetic analysis showed that four mutants, lrd32, lrd39, lrd40 and lrd42, were controlled by one or two recessive loci . Among the 18 lrd mutants, lrd37 and lrd40 conferred non-race-specific resistance to Xanthomonas oryzae pv . oryzae . Gene mapping and cloning of Lrd32 and Lrd40 are under way.

Mol Plant Microbe Interact, 2004 Dec, 17(12), 1348 - 54
The rice bacterial blight resistance gene xa5 encodes a novel form of disease resistance; Lyer AS et al.; The rice xa5 gene for disease resistance to Xanthomonas oryzae pv . oryzae has been positionally cloned and encodes the gamma subunit of transcription factor IIA (TFIIAgamma) . TFIIAgamma is a general eukaryotic transcription factor with no previously known role in disease resistance . xa5 is unusual in that it is recessive and does not conform to one of the typical resistance gene structural classes . Sequencing of TFIIAgamma in resistant and susceptible isolines revealed two nucleotide substitutions resulting in an amino acid change between resistant and susceptible cultivars . This association was conserved across 27 resistant and nine susceptible rice lines in the Aus-Boro group.

J Biol Chem . 2004 Dec 7; {Epub ahead of print}
Associations of the major pseudopilin XpsG with XpsN (GspC) and secretin XpsD of Xanthomonas campestris pv . campestris type II secretion apparatus revealed by crossling analysis; Lee MS et al.; The major pseudopilin XpsG is an essential component of type II secretion apparatus of Xanthomonas campestris pv . campestris . Along with other ancillary pseudopilins, it forms a pilus-like structure spanning between cytoplasmic and outer membranes . Associations of pseudopilins with non-pseudopilin members of type II secretion apparatus were not well documented, probably due to their dynamic or unstable nature . In this study, by treating intact cells with a cleavable cross-linker DSP, followed by metal chelating chromatography and immunoblotting on secretion-positive strains of X . campestris pv . campestris, we discovered associations of XpsGh with XpsN (GspC), as well as XpsD . These associations were detectable in a strain missing all components, but XpsO, of the type II secretion apparatus . However, chromosomal non-polar mutation in each gene exerted different effects upon the association between the other two . The XpsGh/XpsD association is undetectable in xpsN mutant, however restored to a limited extent by overproducing XpsD protein . The XpsGh/XpsN association is unaltered by a lack of XpsD protein or an elevation of its abundance . Co-immune precipitation between XpsN and XpsD, while being independent of XpsG, was nonetheless enhanced by raising XpsG protein level . These observations agree with the proposition that the type II secretion apparatus in a cell may exist as an integrated multiprotein complex with all components working in concert . Moreover, in functional machinery, the association of the major pseudopilin XpsG with secretin XpsD appears strongly dependent on the existence of XpsN, the GspC protein.

Appl Environ Microbiol, 2004 Dec, 70(12), 7388 - 95
Novel type of heme-dependent oxygenase catalyzes oxidative cleavage of rubber (poly-cis-1,4-isoprene); Braaz R et al.; An extracellular protein with strong absorption at 406 nm was purified from cell-free culture fluid of latex-grown Xanthomonas sp . strain 35Y . This protein was identical to the gene product of a recently characterized gene cloned from Xanthomonas sp., as revealed by determination of m/z values and sequencing of selected isolated peptides obtained after trypsin fingerprint analysis . The purified protein degraded both natural rubber latex and chemosynthetic poly(cis-1,4-isoprene) in vitro by oxidative cleavage of the double bonds of poly(cis-1,4-isoprene) . 12-oxo-4,8-dimethyltrideca-4,8-diene-1-al (m/z 236) was identified and unequivocally characterized as the major cleavage product, and there was a homologous series of minor metabolites that differed from the major degradation product only in the number of repetitive isoprene units between terminal functions, CHO-CH2--and--H2-COCH3 . An in vitro enzyme assay for oxidative rubber degradation was developed based on high-performance liquid chromatography analysis and spectroscopic detection of product carbonyl functions after derivatization with dinitrophenylhydrazone . Enzymatic cleavage of rubber by the purified protein was strictly dependent on the presence of oxygen; it did not require addition of any soluble cofactors or metal ions and was optimal around pH 7.0 at 40 degrees C . Carbon monoxide and cyanide inhibited the reaction; addition of catalase had no effect, and peroxidase activity could not be detected . The purified protein was specific for natural rubber latex and chemosynthetic poly(cis-1,4-isoprene) . Analysis of the amino acid sequence deduced from the cloned gene (roxA {rubber oxygenase}) revealed the presence of two heme-binding motifs (CXXCH) for covalent attachment of heme to the protein . Spectroscopic analysis confirmed the presence of heme, and approximately 2 mol of heme per mol of RoxA was found.

Appl Microbiol Biotechnol . 2004 Nov 24; {Epub ahead of print}
Characterisation of a secondary alcohol dehydrogenase from Xanthomonas campestris DSM 3586; Salusjarvi T et al.; The chromosomal locus NP_636946 of Xanthomonas campestris DSM 3586 (ATCC 33913) which was earlier presumed to encode a quinoprotein glucose dehydrogenase has been cloned, expressed in Escherichia coli and the recombinant enzyme has been characterised . It was found to have no glucose dehydrogenase activity but to be active on many different polyols and diols, aliphatic alcohols, certain aldonic acids and amino-sugars . The product of d-gluconic acid oxidation was 5-keto- d-gluconic acid . The enzyme differs from polyol/gluconate dehydrogenases found in Gluconobacter by its single-chain architecture, different substrate specificity and much higher (20- to 30-fold) expression level in E.coli.

Plant Cell Physiol, 2004 Oct, 45(10), 1537 - 42
Ornithine decarboxylase gene (CaODC1) is specifically induced during TMV-mediated but salicylate-independent resistant response in hot pepper; Yoo TH et al.; A gene encoding putative ornithine decarboxylase (ODC) has been isolated by differential screening of a cDNA library from the resistant hot pepper (Capsicum annuum L.) inoculated with avirulent tobacco mosaic virus (TMV) pathotype P0 . In hot pepper plants, transcripts of the CaODC1 (C . annuum ODC1) gene started to accumulate at 24 h post-inoculation of TMV-P0 and the signal was spread systemically . The transcript level of CaODC1 was increased rapidly in a hot pepper resistant to Xanthomonas campestris pv . vesicatoria (Xcv) but not in a susceptible hot pepper after inoculation . These results suggest possible role(s) for CaODC1 in plant defense against a broad range of pathogens including viruses and bacteria.

Mol Plant Microbe Interact, 2004 Nov, 17(11), 1212 - 22
Identification and expression profiling of tomato genes differentially regulated during a resistance response to Xanthomonas campestris pv . vesicatoria; Gibly A et al.; The gram-negative bacterium Xanthomonas campestris pv . vesicatoria is the causal agent of spot disease in tomato and pepper . Plants of the tomato line Hawaii 7981 are resistant to race T3 of X . campestris pv . vesicatoria expressing the type III effector protein AvrXv3 and develop a typical hypersensitive response upon bacterial challenge . A combination of suppression subtractive hybridization and microarray analysis identified a large set of cDNAs that are induced or repressed during the resistance response of Hawaii 7981 plants to X . campestris pv . vesicatoria T3 bacteria . Sequence analysis of the isolated cDNAs revealed that they correspond to 426 nonredundant genes, which were designated as XRE (Xanthomonas-regulated) genes and were classified into more than 20 functional classes . The largest functional groups contain genes involved in defense, stress responses, protein synthesis, signaling, and photosynthesis . Analysis of XRE expression kinetics during the tomato resistance response to X . campestris pv . vesicatoria T3 revealed six clusters of genes with coordinate expression . In addition, by using isogenic X . campestris pv . vesicatoria T2 strains differing only by the avrXv3 avirulence gene, we found that 77% of the identified XRE genes were directly modulated by expression of the AvrXv3 effector protein . Interestingly, 64% of the XRE genes were also induced in tomato during an incompatible interaction with an avirulent strain of Pseudomonas syringae pv . tomato . The identification and expression analysis of X . campestris pv . vesicatoria T3-modulated genes, which may be involved in the control or in the execution of plant defense responses, set the stage for the dissection of signaling and cellular responses activated in tomato plants during the onset of spot disease resistance.

Mol Plant Microbe Interact, 2004 Nov, 17(11), 1192 - 200
Diverse members of the AvrBs3/PthA family of type III effectors are major virulence determinants in bacterial blight disease of rice; Yang B et al.; AvrXa7 is a member of the avBs3/pthA gene family and the only known type III secretion system effector gene from Xanthomonas oryzae pv . oryzae with a major contribution to bacterial growth and lesion formation in bacterial blight disease of rice . We examined the general requirement for effectors of the AvrBs3/PthA family in bacterial blight of rice by identifying effectors from diverse strains of the pathogen . Inactivation of single effector genes in representative strains from Japan, Korea, and the Philippines resulted in severely limited growth in plants . Five strains harbored one gene of the avrBs3/pthA family, while one strain had two genes with the equivalent virulence activity of avrXa7 . Sequence analysis revealed three genes with unique repeat arrangements in comparison to avrXa7 . Comparison of the repetitive regions revealed a potential motif for the group that was also present in the repetitive region of avrBs3 . However, the repetitive region of avrBs3 could not support virulence activity but, in combination with the C-terminal coding region of avrXa7, triggered a Xa7-dependent avirulence reaction . The results revealed diverse members of the avrBs3/pthA gene family with virulence activity in X . oryzae pv . oryzae and supported the hypothesis that bacterial blight disease of rice is highly dependent on a single class of type III effectors . The results also indicated that avrXa7 avirulence specificity is separable from virulence activity.

Proc Natl Acad Sci U S A, 2004 Nov 23, 101(47), 16624 - 9 Epub 2004 Nov 23.
A genetic screen to isolate type III effectors translocated into pepper cells during Xanthomonas infection; Roden JA et al.; The bacterial pathogen Xanthomonas campestris pv . vesicatoria (Xcv) uses a type III secretion system (TTSS) to translocate effector proteins into host plant cells . The TTSS is required for Xcv colonization, yet the identity of many proteins translocated through this apparatus is not known . We used a genetic screen to functionally identify Xcv TTSS effectors . A transposon 5 (Tn5)-based transposon construct including the coding sequence for the Xcv AvrBs2 effector devoid of its TTSS signal was randomly inserted into the Xcv genome . Insertion of the avrBs2 reporter gene into Xcv genes coding for proteins containing a functional TTSS signal peptide resulted in the creation of chimeric TTSS effector::AvrBs2 fusion proteins . Xcv strains containing these fusions translocated the AvrBs2 reporter in a TTSS-dependent manner into resistant BS2 pepper cells during infection, activating the avrBs2-dependent hypersensitive response (HR) . We isolated seven chimeric fusion proteins and designated the identified TTSS effectors as Xanthomonas outer proteins (Xops) . Translocation of each Xop was confirmed by using the calmodulin-dependent adenylate cydase reporter assay . Three xop genes are Xanthomonas spp.-specific, whereas homologs for the rest are found in other phytopathogenic bacteria . XopF1 and XopF2 define an effector gene family in Xcv . XopN contains a eukaryotic protein fold repeat and is required for full Xcv pathogenicity in pepper and tomato . The translocated effectors identified in this work expand our knowledge of the diversity of proteins that Xcv uses to manipulate its hosts.

Mol Microbiol, 2004 Nov, 54(3), 755 - 68
HpaB from Xanthomonas campestris pv . vesicatoria acts as an exit control protein in type III-dependent protein secretion; Buttner D et al.; The hrp (hypersensitive response and pathogenicity) gene cluster of the plant pathogenic bacterium Xanthomonas campestris pv . vesicatoria encodes a type III secretion (TTS) system, which injects bacterial effector proteins into the plant cell . Here, we characterized hpaB (hpa, hrp-associated), which encodes a pathogenicity factor with typical features of a TTS chaperone . We show that HpaB is important for the efficient secretion of at least five effector proteins but is dispensable for the secretion of non-effectors such as XopA and the TTS translocon protein HrpF . GST pull-down assays revealed that HpaB interacts with two unrelated effector proteins, AvrBs1 and AvrBs3, but not with XopA . The HpaB-binding site is located within the first 50 amino acids of AvrBs3 . This region also contains the targeting signal for HpaB-dependent secretion, which is missing in HrpF and XopA . Intriguingly, the N-termini of HrpF and XopA target the AvrBs3Delta2 reporter for translocation in a DeltahpaB mutant but not in the wild-type strain . This indicates that HpaB plays an essential role in the exit control of the TTS system . Our data suggest that HpaB promotes the secretion of a large set of effector proteins and prevents the delivery of non-effectors into the plant cell.

BMC Microbiol . 2004 Oct 09;4(1):40.
Variation suggestive of horizontal gene transfer at a lipopolysaccharide (lps) biosynthetic locus in Xanthomonas oryzae pv . oryzae, the bacterial leaf blight pathogen of rice; Patil PB et al.; BACKGROUND: In animal pathogenic bacteria, horizontal gene transfer events (HGT) have been frequently observed in genomic regions that encode functions involved in biosynthesis of the outer membrane located lipopolysaccharide (LPS) . As a result, different strains of the same pathogen can have substantially different lps biosynthetic gene clusters . Since LPS is highly antigenic, the variation at lps loci is attributed to be of advantage in evading the host immune system . Although LPS has been suggested as a potentiator of plant defense responses, interstrain variation at lps biosynthetic gene clusters has not been reported for any plant pathogenic bacterium . RESULTS: We report here the complete sequence of a 12.2 kb virulence locus of Xanthomonas oryzae pv . oryzae (Xoo) encoding six genes whose products are homologous to functions involved in LPS biosynthesis and transport . All six open reading frames (ORFs) have atypical G+C content and altered codon usage, which are the hallmarks of genomic islands that are acquired by horizontal gene transfer . The lps locus is flanked by highly conserved genes, metB and etfA, respectively encoding cystathionine gamma lyase and electron transport flavoprotein . Interestingly, two different sets of lps genes are present at this locus in the plant pathogens, Xanthomonas campestris pv . campestris (Xcc) and Xanthomonas axonopodis pv . citri (Xac) . The genomic island is present in a number of Xoo strains from India and other Asian countries but is not present in two strains, one from India (BXO8) and another from Nepal (Nepal624) as well as the closely related rice pathogen, Xanthomonas oryzae pv . oryzicola (Xoor) . TAIL-PCR analysis indicates that sequences related to Xac are present at the lps locus in both BXO8 and Nepal624 . The Xoor strain has a hybrid lps gene cluster, with sequences at the metB and etfA ends, being most closely related to sequences from Xac and the tomato pathogen, Pseudomonas syringae pv . tomato respectively . CONCLUSION: This is the first report of hypervariation at an lps locus between different strains of a plant pathogenic bacterium . Our results indicate that multiple HGT events have occurred at this locus in the xanthomonad group of plant pathogens.

Yi Chuan Xue Bao, 2004 Jul, 31(7), 724 - 9
{Mapping of a new resistance gene to bacterial blight in rice line introgressed from Oryza officinalis}; Tan GX et al.; Rice line 'B5', which was derived from the wild rice Oryza officinalis Wall ex Watt through introgression, has been proved to be high resistant to brown planthopper, whitebacked planthopper and bacterial blight (Xanthomonas oryzae pv . oryzae) . In this study, the resistance to bacterial blight of 187 recombinant inbred lines (RILs) from a cross between ' B5' and 'Minghui63' were evaluated and RFLP markers linked to the resistance gene were identified by bulked segregant analysis . Analysis of the molecular marker linkage map and the data of the lesion length of RILs located the resistant gene within a 1 . 3 cM region flanked by RFLP markers C904 and R596 on chromosome 1 . This locus contributed to 52.96% of the phenotypic variance of resistance in the population, and is considered to be a new locus as compared with other resistant genes to bacterial blight that have been reported . We tentatively designate this gene as Xa29(t) . This newly tagged gene introgressed from wild rice is valuable to molecular marker-assisted selection for multiple resistant materials in rice breeding programme . Furthermore, it provides information for cloning the resistant gene Xa29(t) in rice.

Prikl Biokhim Mikrobiol, 2004 Jul-Aug, 40(4), 435 - 41
{Hydrolysis of peptides by immobilized bacterial peptide hydrolases}; Nekliudov AD et al.; The feasibility of hydrolysis of a mixture of peptides with an enzyme from the bacterium Xanthomonas rubrilineans, displaying a peptidase activity and immobilized on aluminum oxide, was studied . Kinetic schemes and equations allowing for approaching quantitative description of peptide hydrolysis in complex mixtures containing free amino acids and peptides were obtained . It was demonstrated that as a result of hydrolysis, the content of free amino acids in hydrolysates decreased 2.5- to 3-fold and the molecular weight of the constituent peptides, 2-fold.

Plant Physiol, 2004 Sep, 136(1), 2862 - 74 Epub 2004 Sep 03.
The pepper transcription factor CaPF1 confers pathogen and freezing tolerance in Arabidopsis; Yi SY et al.; An ERF/AP2-type transcription factor (CaPF1) was isolated by differential-display reverse transcription-PCR, following inoculation of the soybean pustule pathogen Xanthomonas axonopodis pv glycines 8ra, which induces hypersensitive response in pepper (Capsicum annuum) leaves . CaPF1 mRNA was induced under conditions of biotic and abiotic stress . Higher levels of CaPF1 transcripts were observed in disease-resistant tissue compared with susceptible tissue . CaPF1 expression was additionally induced using various treatment regimes, including ethephon, methyl jasmonate, and cold stress . To determine the role of CaPF1 in plants, transgenic Arabidopsis and tobacco (Nicotiana tabacum) plants expressing higher levels of CaPF1 were generated . Gene expression analyses of transgenic Arabidopsis and tobacco revealed that the CaPF1 level in transgenic plants affects expression of genes that contain either a GCC or a CRT/DRE box in their promoter regions . Furthermore, transgenic Arabidopsis plants expressing CaPF1 displayed tolerance against freezing temperatures and enhanced resistance to Pseudomonas syringae pv tomato DC3000 . Disease tolerance was additionally observed in CaPF1 transgenic tobacco plants . The results collectively indicate that CaPF1 is an ERF/AP2 transcription factor in hot pepper plants that may play dual roles in response to biotic and abiotic stress in plants.

DNA Seq, 2004 Apr, 15(2), 110 - 7
Cloning and characterization of a novel avirulence gene (arp3) from Xanthomonas oryzae pv . oryzae; Liang B et al.; A novel avirulence gene was cloned from Xanthomonas oryzae pv . oryzae strain PX0339, which is the standard representative of the Philippines race 9a . The full-length gene spans 2118 bp and encodes a protein of 705 amino acids . BLAST search in NCBI indicated that the gene belongs to avrBs3 gene family, and designated arp3 (AvrBs3-related protein 3, arp3) . The central region of the arp3 contains only 5.5 copies of 102bp repeats, the smallest copy number of repeats found in avrBs3 gene family by now . Together with the repeats is heptad repeats, resembling leucine zippers . Three functional nuclear localization signals and an acidic activation domain are also found in the C-terminal region . However, the arp3 lacks of two segments in its N-terminal region, which is unique in avrBs3 gene family . Southern blotting data showed that the arp3 is present as a single-copy in genomic DNA of PX0339 and locus in plasmid clone . The arp3 could be expressed in vitro in Escherichia coli BL21 and a 128kDa fusion protein was detected by Western analysis.

J Bacteriol, 2004 Sep, 186(18), 6186 - 97
New protein-protein interactions identified for the regulatory and structural components and substrates of the type III Secretion system of the phytopathogen Xanthomonas axonopodis Pathovar citri; Alegria MC et al.; We have initiated a project to identify protein-protein interactions involved in the pathogenicity of the bacterial plant pathogen Xanthomonas axonopodis pv . citri . Using a yeast two-hybrid system based on Gal4 DNA-binding and activation domains, we have focused on identifying interactions involving subunits, regulators, and substrates of the type III secretion system coded by the hrp (for hypersensitive response and pathogenicity), hrc (for hrp conserved), and hpa (for hrp associated) genes . We have identified several previously uncharacterized interactions involving (i) HrpG, a two-component system response regulator responsible for the expression of X . axonopodis pv . citri hrp operons, and XAC0095, a previously uncharacterized protein encountered only in Xanthomonas spp.; (ii) HpaA, a protein secreted by the type III secretion system, HpaB, and the C-terminal domain of HrcV; (iii) HrpB1, HrpD6, and HrpW; and (iv) HrpB2 and HrcU . Homotropic interactions were also identified for the ATPase HrcN . These newly identified protein-protein interactions increase our understanding of the functional integration of phytopathogen-specific type III secretion system components and suggest new hypotheses regarding the molecular mechanisms underlying Xanthomonas pathogenicity.

BMC Evol Biol . 2004 Aug 27;4(1):29.
Different patterns of evolution for duplicated DNA repair genes in bacteria of the Xanthomonadales group; Martins-Pinheiro M et al.; BACKGROUND: DNA repair genes encode proteins that protect organisms against genetic damage generated by environmental agents and by-products of cell metabolism . The importance of these genes in life maintenance is supported by their high conservation, and the presence of duplications of such genes may be easily traced, especially in prokaryotic genomes . RESULTS: The genome sequences of two Xanthomonas species were used as the basis for phylogenetic analyses of genes related to DNA repair that were found duplicated . Although 16S rRNA phylogenetic analyses confirm their classification at the basis of the gamma proteobacteria subdivision, differences were found in the origin of the various genes investigated . Except for lexA, detected as a recent duplication, most of the genes in more than one copy are represented by two highly divergent orthologs . Basically, one of such duplications is frequently positioned close to other gamma proteobacteria, but the second is often positioned close to unrelated bacteria . These orthologs may have occurred from old duplication events, followed by extensive gene loss, or were originated from lateral gene transfer (LGT), as is the case of the uvrD homolog . CONCLUSIONS: Duplications of DNA repair related genes may result in redundancy and also improve the organisms' responses to environmental challenges . Most of such duplications, in Xanthomonas, seem to have arisen from old events and possibly enlarge both functional and evolutionary genome potentiality.

Appl Biochem Biotechnol, 1999 Dec, 82(3), 175 - 84
Xanthan Gum Production by Xanthomonas campestris w.t . Fermentation from Chestnut Extract; Liakopoulou-Kyriakides M et al.; Xanthomonas campestris w.t . was used for production of xanthan gum in fermentations with chestnut flour for the first time . Fermentations were carried out with either chestnut flour or its soluble sugars (33.5%) and starch (53.6%), respectively, at 28 degrees C and 200 rpm at initial pH 7.0 in flasks . The effect of agitation rate (at 200, 400, and 600 rpm) on xanthan gum production was also studied in a 2-L batch reactor . It was found that xanthan production reaches a maximum value of 3.3 g/100 mL at 600 rpm and 28 degrees C at 45 h.

Appl Biochem Biotechnol, 2004 Jul-Sep, 118(1-3), 305 - 12
Xanthan gum production from cassava bagasse hydrolysate with Xanthomonas campestris using alternative sources of nitrogen; Woiciechowski AL et al.; Cassava bagasse was hydrolyzed using HCl and the hydrolysate was used for the production of xanthan gum using a bacterial culture of Xanthomonas campestris . Cassava bagasse hydrolysate with an initial concentration of approx 20 g of glucose/L proved to be the best substrate concentration for xanthan gum production . Among the organic and inorganic nitrogen sources tested to supplement the medium-urea, yeast extract, peptone, potassium nitrate, and ammonium sulfate-potassium nitrate was most suitable . Ammonium sulfate was the least effective for xanthan gum production, and it affected sugar utilization by the bacterial culture . In media with an initial sugar concentration of 48.6 and 40.4 g/L, at the end of fermentation about 30 g/L of sugars was unused . Maximum xanthan gum (about 14 g/L) was produced when fermentation was carried out with a medium containing 19.8 g/L of initial reducing sugars supplemented with potassium nitrate and fermented for 72 h, and it remained almost the same until the end of fermentation (i.e., 96 h).

Appl Environ Microbiol, 2004 Aug, 70(8), 4486 - 90
Bactericidal activity of glycinecin A, a bacteriocin derived from Xanthomonas campestris pv . glycines, on phytopathogenic Xanthomonas campestris pv . vesicatoria cells; Pham HT et al.; The ability of glycinecin A, a bacteriocin derived from Xanthomonas campestris pv . glycines 8ra, to kill closely related bacteria has been demonstrated previously by our group . In the present study, we aimed at determining the glycinecin A-induced cause of death . Treatment with glycinecin A caused slow dissipation of membrane potential and rapid depletion of the pH gradient . Glycinecin A treatment also induced leakage of potassium ions from X . campestris pv . vesicatoria YK93-4 cells and killed sensitive bacterial cells in a dose-dependent manner . Sensitive cells were killed within 2 h of incubation, most likely due to the potassium ion efflux caused by glycinecin A . These results suggest that the bactericidal mechanism of action of glycinecin A is correlated with the permeability of membranes to hydroxyl and potassium ions, leading to the lethal activity of the bacteriocin on the target bacteria.

Annu Rev Phytopathol, 2004, 42, 385 - 414
Type III secretion system effector proteins: double agents in bacterial disease and plant defense; Alfano JR et al.; Many phytopathogenic bacteria inject virulence effector proteins into plant cells via a Hrp type III secretion system (TTSS) . Without the TTSS, these pathogens cannot defeat basal defenses, grow in plants, produce disease lesions in hosts, or elicit the hypersensitive response (HR) in nonhosts . Pathogen genome projects employing bioinformatic methods to identify TTSS Hrp regulon promoters and TTSS pathway targeting signals suggest that phytopathogenic Pseudomonas, Xanthomonas, and Ralstonia spp . harbor large arsenals of effectors . The Hrp TTSS employs customized cytoplasmic chaperones, conserved export components in the bacterial envelope (also used by the TTSS of animal pathogens), and a more specialized set of TTSS-secreted proteins to deliver effectors across the plant cell wall and plasma membrane . Many effectors can act as molecular double agents that betray the pathogen to plant defenses in some interactions and suppress host defenses in others . Investigations of the functions of effectors within plant cells have demonstrated the plasma membrane and nucleus as subcellular sites for several effectors, revealed some effectors to possess cysteine protease or protein tyrosine phosphatase activity, and provided new clues to the coevolution of bacterium-plant interactions.

Annu Rev Phytopathol, 2004, 42, 163 - 84
Comparative genomics analyses of citrus-associated bacteria; Moreira LM et al.; Xylella fastidiosa 9a5c (XF-9a5c) and Xanthomonas axonopodis pv . citri (XAC) are bacteria that infect citrus plants . Sequencing of the genomes of these strains is complete and comparative analyses are now under way with the genomes of other bacteria of the same genera . In this review, we present an overview of this comparative genomic work . We also present a detailed genomic comparison between XF-9a5a and XAC . Based on this analysis, genes and operons were identified that might be relevant for adaptation to citrus . XAC has two copies of a type II secretion system, a large number of cell wall-degrading enzymes and sugar transporters, a complete energy metabolism, a whole set of avirulence genes associated with a type III secretion system, and a complete flagellar and chemotatic system . By contrast, XF-9a5c possesses more genes involved with type IV pili biosynthesis than does XAC, contains genes encoding for production of colicins, and has 4 copies of Type I restriction/modification system while XAC has only one.

J Biol Chem, 2004 Oct 8, 279(41), 42462 - 8 Epub 2004 Jul 26.
Evidence for a new sub-class of methionine sulfoxide reductases B with an alternative thioredoxin recognition signature; Neiers F et al.; Methionine sulfoxide reductases catalyze the reduction of protein-bound methionine sulfoxide back to methionine via a thioredoxin-recycling process . Two classes of methionine sulfoxide reductases, called MsrA and MsrB, exist that display opposite stereoselectivities toward the sulfoxide function . Although they are structurally unrelated, they share a similar chemical mechanism that includes three steps with 1) formation of a sulfenic acid intermediate with a concomitant release of 1 mol of methionine per mole of enzyme; 2) formation of an intradisulfide Msr bond; and 3) reduction of the oxidized Msr by thioredoxin . In the MsrBs that have been biochemically, enzymatically, and structurally characterized so far, the cysteine involved in the regeneration of the catalytic Cys-117 is Cys-63 . Cys-117 is located on a beta strand, whereas the recycling Cys-63 is on a loop near Cys-117 . The distance between the two cysteines is compatible with formation of the Cys-117/Cys-63 intradisulfide bond . Analyses of MsrB sequences show that at least 37% of the MsrBs do not possess the recycling Cys-63 . In the present study, it is shown that Cys-31 in the Xanthomonas campestris MsrB, which is located on another loop, can efficiently substitute for Cys-63 . Such a result implies flexibility of the MsrB structures, at least of the loops on which Cys-31 or Cys-63 are located . The fact that about 25% of the putative MsrBs have no recycling cysteine supports other recycling processes in which thioredoxin is not operative.

Indian J Exp Biol, 2003 Jan, 41(1), 78 - 81
Effect of phenol on ultra structure and plasmid DNA of Xanthomonas oryzae pv . oryzae; Mohan N et al.; Most phenolic substances of plant origin are toxic to microorganisms and they confer some degree of protection to plants against phytopathogens . Xanthomonas oryzae pv . oryzae, bacterial blight pathogen of rice (Oryza sativa) was treated with phenol (monohydroxy benzene) and its effects on the morphology and cytological changes of the bacterium were studied . Total lysis of cells occurred with 5 mM conc of phenol while at 2 mM conc, the cell walls became rough and cell contents started shrinking . Plasmids isolated from both treated (2 mM) and control cells did not show any marked difference under electron microscope except that they differed in their quantity and might influence pathogenicity.

J Appl Microbiol, 1998 Jan, 84(1), 115 - 24
Phenotypic diversity of Xanthomonas sp . mangiferaeindicae; Pruvost O et al.; Carbohydrate utilization profiles by means of the API (Appareils et Procedes d'Identification) system and sensitivity to antibiotics and heavy metal salts of 68 Xanthomonas sp . mangiferaeindicae strains isolated in nine countries from mango (Mangifera indica L.) and other genera of the Anacardiaceae were examined to assess the variability of the taxon . The strains could be separated into 10 groups according to Ward clustering . Apigmented strains isolated from the pepper tree {syn . Brazilian pepper} (Schinus terebenthifolius Raddi) could not be clearly differentiated from most apigmented strains isolated from mango . Yellow-pigmented strains isolated from mango in Brazil and Reunion Island, apigmented strains isolated from mango in Brazil and from ambarella in the French West Indies, clustered in distinct groups . The results are consistent with those of other studies, based on isozyme analysis of esterase, phosphoglucomutase and superoxide dismutase, and hrp-RFLP analysis; they indicate the need for a comprehensive taxonomic evaluation of xanthomonads associated with Anacardiaceae.

Mol Plant Microbe Interact, 2004 Jul, 17(7), 805 - 15
Basal defenses induced in pepper by lipopolysaccharides are suppressed by Xanthomonas campestris pv . vesicatoria; Keshavarzi M et al.; The nonpathogenic hrcC mutant of Xanthomonas campestris pv . vesicatoria 85-10::hrpA22 multiplied in pepper leaves if it was mixed with pathogenic strains of X . campestris pv . vesicatoria . Reactions to the mutant alone included localized deposition of phenolics and callose in papillae, and alterations to the plant cell wall leading to increased electron density . Electron microscopy showed that the localized responses were suppressed in the presence of wild-type bacteria but other wall changes occurred at some sites, involving cellulose-rich ingrowth of the wall . Multiplication of the hrp mutant in mixed inocula was confirmed by tagging 85-10::hrpA22 using immunocytochemical location of AvrBs3 expressed from the plasmid pD36 . Elicitors of callose deposition and other wall changes were isolated from the hrcC mutant . Activity in extracts of bacteria was attributed to the presence of high molecular weight lipopolysaccharides (LPS) . Wild-type X . campestris pv . vesicatoria suppressed induction of structural changes caused by purified LPS . Results obtained suggest that effector proteins produced by phytopathogenic bacteria and delivered by the type III secretion system may have a key role in suppressing the basal defense responses activated by bacterial LPS, which lead to restricted multiplication of nonpathogens such as hrp mutants.

Mol Plant Microbe Interact, 2004 Jul, 17(7), 771 - 9
The avrRxo1 gene from the rice pathogen Xanthomonas oryzae pv . oryzicola confers a nonhost defense reaction on maize with resistance gene Rxo1; Zhao B et al.; Maize lines that contain the single dominant gene Rxo1 exhibit a rapid hypersensitive response (HR) after infiltration with the rice bacterial streak pathogen Xanthomonas oryzae pv . oryzicola, but not with the rice bacterial blight pathogen X . oryzae pv . oryzae . The avirulence effector gene that corresponds to Rxo1, designated avrRxo1, was identified in an X . oryzae pv . oryzicola genomic library . When introduced into X . oryzae pv . oryzae, clones containing avrRxo1 induced an HR on maize with Rxo1, but not on maize without Rxo1 . The avrRxo1 gene is 1,266 bp long and shows no significant homology to any database sequences . When expressed in an X . oryzae pv . oryzae hrpC mutant that is deficient in the type III secretion system, avrRxo1 did not elicit the HR, indicating that the avrRxo1-Rxo1 interaction is dependent on type III secretion . Transient expression of avrRxo1 in onion cells after biolistic delivery revealed that the protein product was associated with the plasma membrane . Transient expression in maize lines carrying Rxo1 resulted in cell death, suggesting that AvrRxo1 functions from inside maize cells to elicit Rxo1-dependent pathogen recognition.

J Microbiol Methods, 2004 Aug, 58(2), 281 - 4
A rapid and sensitive method for the detection of Xanthomonas fragariae, causal agent of angular leafspot disease in strawberry plants; Stoger A et al.; Angular leaf spot is a bacterial disease caused by Xanthomonas fragariae . It has become a serious disease in the USA and Europe in recent years . Several detection procedures are described for this plant pathogen . However, they are either too time-consuming, too insensitive or impractical when handling a large number of samples routinely . Here we describe a modified protocol of the REDExtract-N-Amp Plant PCR-Kit for the detection of X . fragariae in planta and demonstrate that it provides greater sensitivity, speed and high throughput potential than methods previously described.

Mol Plant Microbe Interact, 2004 Jun, 17(6), 633 - 43
Characterization of the Xanthomonas AvrXv4 effector, a SUMO protease translocated into plant cells; Roden J et al.; Homologs of the Yersinia virulence factor YopJ are found in both animal and plant bacterial pathogens, as well as in plant symbionts . The conservation of this effector family indicates that several pathogens may use YopJ-like proteins to regulate bacteria-host interactions during infection . YopJ and YopJ-like proteins share structural homology with cysteine proteases and are hypothesized to functionally mimic small ubiquitin-like modifier (SUMO) proteases in eukaryotic cells . Strains of the phytopathogenic bacterium Xanthomonas campestris pv . vesicatoria are known to possess four YopJ-like proteins, AvrXv4, AvrBsT, AvrRxv, and XopJ . In this work, we have characterized AvrXv4 to determine if AvrXv4 functions like a SUMO protease in planta during Xanthomonas-plant interactions . We provide evidence that X . campestris pv . vesicatoria secretes and translocates the AvrXv4 protein into plant cells during infection in a type III-dependent manner . Once inside the plant cell, AvrXv4 is localized to the plant cytoplasm . By performing AvrXv4 deletion and mutational analysis, we have identified amino acids required for type III delivery and for host recognition . We show that AvrXv4 recognition by resistant plants requires a functional protease catalytic core, the domain that is conserved in all of the putative YopJ-like cysteine proteases . We also show that AvrXv4 expression in planta leads to a reduction in SUMO-modified proteins, demonstrating that AvrXv4 possesses SUMO isopeptidase activity . Overall, our studies reveal that the YopJ-like effector AvrXv4 encodes a type III SUMO protease effector that is active in the cytoplasmic compartment of plant cells.

Mol Plant Microbe Interact, 2004 Jun, 17(6), 602 - 12
RaxH/RaxR: a two-component regulatory system in Xanthomonas oryzae pv . oryzae required for AvrXa21 activity; Burdman S et al.; Xanthomonas oryzae pv . oryzae is the causal agent of bacterial leaf blight, one of the most serious diseases in rice . X . oryzae pv . oryzae Philippine race 6 (PR6) strains are unable to establish infection in rice lines expressing the resistance gene Xa21 . Although the pathogen-associated molecule that triggers the Xa21-mediated defense response (AvrXa21) is unknown, six rax (required for AvrXa21 activity) genes encoding proteins involved in sulfur metabolism and Type I secretion were recently identified . Here, we report on the identification of two additional rax genes, raxR and raxH, which encode a response regulator and a histidine protein kinase of two-component regulatory systems, respectively . Null mutants of PR6 strain PXO99 that are impaired in either raxR, raxH, or both cause lesions significantly longer and grow to significantly higher levels than does the wild-type strain in Xa21-rice leaves . Both raxR and raxH mutants are complemented to wild-type levels of AvrXa21 activity by introduction of expression vectors carrying raxR and raxH, respectively . These null mutants do not affect AvrXa7 and AvrXa10 activities, as observed in inoculation experiments with Xa7- and Xa10-rice lines . Western blot and raxR/gfp promoter-reporter analyses confirmed RaxR expression in X . oryzae pv . oryzae . The results of promoter-reporter studies also suggest that the previously identified raxSTAB operon is a target for RaxH/RaxR regulation . Characterization of the RaxH/RaxR system provides new opportunities for understanding the specificity of the X . oryzae pv . oryzae-Xa21 interaction and may contribute to the identification of AvrXa21.

Mol Plant Microbe Interact, 2004 Jun, 17(6), 593 - 601
Bacterial genes involved in type I secretion and sulfation are required to elicit the rice Xa21-mediated innate immune response; da Silva FG et al.; Innate immunity to microorganisms relies on the specific sensing of pathogen-associated molecules by host recognition receptors . Whereas studies in animals have largely focused on the recognition of extracellular pathogen-associated molecules by the TLR (toll-like receptor) superfamily, few studies have been carried out in plants, and it is not understood how these molecules are secreted or modified . The rice Xa21 gene encodes a receptor-like kinase that provides immunity against strains of the bacterial pathogen Xanthomonas oryzae pv . oryzae carrying AvrXa21 activity . We identified four X . oryzae pv . oryzae genes that are required for AvrXa21 activity . raxA, raxB, and raxC encode proteins with similarity to a membrane fusion protein, an ATP-binding cassette transporter, and an outer membrane protein, respectively, of bacterial type I secretion systems . The fourth gene, raxST, encodes a sulfotransferase-like protein . Sequence analysis of three naturally occurring X . oryzae pv . oryzae strains no longer recognized by Xa21 revealed alterations in the raxST and raxA genes . The raxC gene complemented an Escherichia coli tolC mutant for secretion of a double glycine-leader peptide confirming the function of raxC in type I secretion . These results indicate that bacterial type I secretion is necessary for Xa21-mediated recognition and immunity and further suggest that type I secretion and modification of pathogen-associated molecules play an important role in triggering the innate immune response in rice.

Planta, 2004 Sep, 219(5), 797 - 806 Epub 2004 Jun 08.
Molecular characterization of pepper germin-like protein as the novel PR-16 family of pathogenesis-related proteins isolated during the resistance response to viral and bacterial infection; Park CJ et al.; To understand the molecular defense mechanism controlling the hypersensitive response (HR) better, we examined the hot pepper plant (Capsicum annuum L . cv . Bugang), which exhibits an HR in response to infection by Tobacco mosaic virus pathotype P0 (TMV-P0) . A full-length cDNA clone was isolated by differential screening of a cDNA library that was constructed with mRNA extracted from hot pepper leaves during the resistance response to TMV-P0 . The predicted amino acid sequence of the cDNA clone exhibited a high sequence similarity to germin-like protein (GLP) . The CaGLP1 (Capsicum annuum GLP1) cDNA contains a single open reading frame of 660 bp encoding 220 amino acid residues . Upon inoculation with TMV or Xanthomonas, CaGLP1 transcripts were specifically accumulated in the incompatible interaction but not in the compatible interaction . In plants treated with salicylic acid (SA) or ethephon, which are signal molecules in the defense-related signal transduction pathway, CaGLP1 transcripts were accumulated rapidly . As far as we know, this is the first report that plant GLPs can be specifically induced during a defense response against viral infection . These data suggest that in the hot pepper plant CaGLP1 may be involved in the defense response to viral pathogens, and thus be classified as a new family of PR proteins, 'PR-16'.

J Mol Microbiol Biotechnol, 2003, 6(3-4), 145 - 54
Molecular genetic analyses of potential beta-galactosidase genes in Xanthomonas campestris; Yang TC et al.; Xanthomonas campestris pv . campestris, which displays no significant beta-1,4-D-galactopyranosidase activity, has three annotated beta-galactosidase genes in the sequenced genome, designated galA, galB and galC herein . GalA and GalB are similar to glycosyl hydrolase (GH) family 2 enzymes, including Escherichia coli LacZ . galA and galB cannot express detectable activity even after being cloned in-frame and driven by the vector's promoter . GalC is a GH35 enzyme homologous to the Xanthomonas axonopodis pv . manihotis Bga . The latter cleaves beta,1-3-linked galactose 1,000 times faster than beta,1-4-linked galactose and is not responsible for lactose utilization . In X . campestris pv . campestris cells, GalC is readily detectable by Western blotting, and the levels can be increased by cloning the gene under the control of the vector's promoter . Results of insertional mutation, transcriptional fusion assay and Western blotting indicated that galC, clustered with several GH genes, is cotranscribed with the upstream gene(s) and is expressed constitutively . Xc17L is a previously isolated mutant with elevated beta-galactosidase activity and a greatly improved ability to grow on lactose . Results of DNA sequencing of Xc17L galA, galB and galC, enzyme assays of galA, galB and galC mutants derived from Xc17L, and Western blotting of GalC in Xc17L indicated that the three beta-galactosidase genes do not encode the elevated beta-galactosidase activity in Xc17L . The presence of a fourth beta-galactosidase gene is proposed .

Plant Physiol, 2004 May, 135(1), 530 - 8 Epub 2004 May 07.
The role of the jasmonate response in plant susceptibility to diverse pathogens with a range of lifestyles; Thaler JS et al.; Plants defend themselves against attack from insects and pathogens with various resistance strategies . The jasmonate and salicylate signaling pathways are two induced responses that protect plants against these attackers . Knowledge of the range of organisms that are affected by each response is important for understanding how plants coordinate their defenses against multiple attackers and the generality of effect of different resistance mechanisms . The jasmonate response is known to protect plants against a wide range of insect herbivores; in this study, we examined the role of the jasmonate response in susceptibility to eight pathogens with diverse lifestyles in the laboratory and field . Recent biochemical models suggest that the lifestyle of the pathogen (necrotroph versus biotroph) should predict whether the jasmonate response will be involved in resistance . We tested this by examining the susceptibility of wild-type (cv Castlemart with no known genes for resistance to the pathogens used) and jasmonate-deficient mutant tomato (Lycopersicon esculentum) plants (def1) and by employing rescue treatments of the mutant . Plant susceptibility to five of the eight pathogens we examined was reduced by the jasmonate response, including two bacteria (Pseudomonas syringae and Xanthomonas campestris), two fungi (Verticillium dahliae and Fusarium oxysporum f . sp . lycopersici), and an oomycete (Phytophthora infestans) . Susceptibility to three fungi was unaffected (Cladosporium fulvum, Oidium neolycopersici, and Septoria lycopersici) . Our results indicate that the jasmonate response reduces damage by a wide range of pathogens from different lifestyles, a result that contrasts with the emerging picture of diseases on Arabidopsis . Thus, the generality of jasmonate-based resistance of tomato challenges the view that ecologically distinct plant parasites are resisted via different mechanisms.

Int J Pharm, 2004 Mar 1, 271(1-2), 197 - 205
Evaluation of xanthan and highly substituted galactomannan from M . scabrella as a sustained release matrix; Ughini F et al.; A highly substituted galactomannan (G) from Mimosa scabrella Bentham (Man:Gal 1.1:1), isolated from the seeds of a Brazilian leguminous tree and xanthan (X), an exopolysaccharide secreted by Xanthomonas campestris (Keltrol), were evaluated as a hydrophilic matrix system (XG) for controlled release (CR) of diclofenac sodium (DS) in tablets and capsules . The performance of XG (2:1) matrices containing 50 mg (A) or 100 mg (B) of DS was compared with a commercial CR product of DS . The drug release studies were carried out using a dissolution apparatus (paddle method) with gradual increase of pH values, from pH 1.4, to pH 4.0 (after 1 h) and to pH 6.8 (after 2 h) . The results suggested the potential of XG systems as release retarding materials, which released 78.6 and 35.1% of drug after 24 h for capsules (A) and tablets (A), respectively . Drug release decreased with the increase of amount of drug and it is dependent of dosage form . Analysis of release data indicate a rather zero-order drug release with the erosion mechanism playing a dominant role.

J Bacteriol, 2004 May, 186(10), 2946 - 55
Functional dissection of the XpsN (GspC) protein of the Xanthomonas campestris pv . campestris type II secretion machinery; Lee HM et al.; Type II secretion machinery is composed of 12 to 15 proteins for translocating extracellular proteins across the outer membrane . XpsL, XpsM, and XpsN are components of such machinery in the plant pathogen Xanthomonas campestris pv . campestris . All are bitopic cytoplasmic-membrane proteins, each with a large C-terminal periplasmic domain . They have been demonstrated to form a dissociable ternary complex . By analyzing the C-terminally truncated XpsN and PhoA fusions, we discovered that truncation of the C-terminal 103 residues produced a functional protein, albeit present below detectable levels . Furthermore, just the first 46 residues, encompassing the membrane-spanning sequence (residues 10 to 32), are sufficient to keep XpsL and XpsM at normal abundance . XpsN46(His6), synthesized in Escherichia coli, is able to associate in a membrane-mixing experiment with the XpsL-XpsM complex preassembled in X . campestris pv . campestris . The XpsN N-terminal 46 residues are apparently sufficient not only for maintaining XpsL and XpsM at normal levels but also for their stable association . The membrane-spanning sequence of XpsN was not replaceable by that of TetA . However, coimmunoprecipitation with XpsL and XpsM was observed for XpsN97::PhoA, but not XpsN46::PhoA . Only XpsN97::PhoA is dominant negative . Single alanine substitutions for three charged residues within the region between residues 47 and 97 made the protein nonfunctional . In addition, the R78A mutant XpsN protein was pulled down by XpsL-XpsM(His6) immobilized on an Ni-nitrilotriacetic acid column to a lesser extent than the wild-type XpsN . Therefore, in addition to the N-terminal 46 residues, the region between residues 47 and 97 of XpsN probably also plays an important role in interaction with XpsL-XpsM.

Theor Appl Genet, 2004 Mar, 108(5), 800 - 7 Epub 2003 Oct 31.
High-resolution genetic mapping of Xa27(t), a new bacterial blight resistance gene in rice, Oryza sativa L; Gu K et al.; Bacterial blight of rice, caused by Xanthomonas oryzae pv . oryzae ( Xoo) (Ishyama) Dye, is one of the serious diseases prevalent throughout Asia . In a previous study, a resistance ( R) locus was transferred from the tetraploid wild rice Oryza minuta to the cultivated rice species, Oryza sativa L . Here, we report the fine genetic mapping of the R locus, tentatively designated as Xa27(t) . We performed disease evaluation with an Xa27(t) near-isogenic line, IRBB27, testing 35 Xoo strains collected from 11 countries . The Xa27(t) locus conferred a high level of resistance to 27 strains and moderate resistance to three strains . Resistance of the Xa27(t) gene was developmentally regulated in IRBB27 and showed semi-dominant or a dosage effect in the cv . CO39 genetic background . As a prelude to cloning Xa27(t), a molecular mapping strategy was employed with a large mapping population consisting of 3,875 gametes . Three molecular markers, M336, M1081, and M1059, closely linked to Xa27(t), were identified to facilitate the mapping of Xa27(t) to the long arm of chromosome 6 . The Xa27(t) locus was confirmed by chromosome landing of M1081 and M1095 markers on the rice genome . Markers derived from the genomic sequence of O . sativa cv . Nipponbare were used to further saturate the Xa27(t) genomic region . Xa27(t) was finally located within a genetic interval of 0.052 cM, flanked by markers M964 and M1197, and co-segregated with markers M631, M1230, and M449.

Plant Physiol, 2004 May, 135(1), 561 - 73 Epub 2004 Apr 23.
Capsicum annuum tobacco mosaic virus-induced clone 1 expression perturbation alters the plant's response to ethylene and interferes with the redox homeostasis; Shin R et al.; Capsicum annuum tobacco mosaic virus (TMV)-induced clone 1 (CaTin1) gene was expressed early during incompatible interaction of hot pepper (Caspsicum annuum) plants with TMV and Xanthomonas campestris . RNA-blot analysis showed that CaTin1 gene was expressed only in roots in untreated plants and induced mainly in leaf in response to ethylene, NaCl, and methyl viologen but not by salicylic acid and methyl jasmonate . The ethylene dependence of CaTin1 induction upon TMV inoculation was demonstrated by the decrease of CaTin1 expression in response to several inhibitors of ethylene biosynthesis or its action . Transgenic tobacco (Nicotiana tabacum) plants expressing CaTin1 gene in sense- or antisense-orientation showed interesting characteristics such as the accelerated growth and the enhanced resistance to biotic as well as abiotic stresses . Such characteristics appear to be caused by the elevated level of ethylene and H2O2 . Moreover, in transgenic plants expressing antisense CaTin1 gene, the expression of some pathogenesis-related genes was enhanced constitutively, which may be mainly due to the increased ethylene level . The promoter of CaTin1 has four GCC-boxes, two AT-rich regions, and an elicitor-inducible W-box . The induction of the promoter activity by ethylene depends on GCC-boxes and by TMV on W-box . Taken together, we propose that the CaTin1 up-regulation or down-regulation interferes with the redox balance of plants leading to the altered response to ethylene and biotic as well as abiotic stresses.

Mol Plant Microbe Interact, 2004 Apr, 17(4), 414 - 27
Albicidin pathotoxin produced by Xanthomonas albilineans is encoded by three large PKS and NRPS genes present in a gene cluster also containing several putative modifying, regulatory, and resistance genes; Royer M et al.; Xanthomonas albilineans, which causes leaf scald disease of sugarcane, produces a highly potent pathotoxin called albicidin . We report here sequencing and homology analysis of the major gene cluster, XALB1 (55,839 bp), and a second, smaller region, XALB2 (2,986 bp), involved in albicidin biosynthesis . XALB1 contains 20 open reading frames, including i) three large genes with a modular architecture characteristic of polyketide synthases (PKSs) and nonribosomal peptide synthases (NRPSs) and ii) several putative modifying, regulatory, and resistance genes . Sequencing and complementation studies of six albicidin-defective mutants enabled us to confirm the involvement of the three PKS and NRPS genes encoded by XALB1 in albicidin production . XALB2 contains only one gene that is required for post-translational activation of PKS and NRPS enzymes, confirming the involvement of these enzymes in albicidin biosynthesis . In silico analysis of these three PKS or NRPS enzymes allowed us to propose a model for the albicidin backbone assembly and to gain insight into the structural features of this pathotoxin . This is the first description of a complete mixed PKS-NRPS gene cluster for toxin production in the genus Xanthomonas.

Bioinformatics, 2004 Oct 12, 20(15), 2473 - 5 Epub 2004 Apr 08.
G-PRIMER: greedy algorithm for selecting minimal primer set; Wang J et al.; G-PRIMER, a web-based primer design program, has been developed to compute a minimal primer set specifically annealed to all the open reading frames in a given microbial genome . This program has been successfully used in the microarray experiment for analyzing the expression of genes in the Xanthomonas campestris genome . AVAILABILITY: It is available at Its source code is available upon request.

Sichuan Da Xue Xue Bao Yi Xue Ban, 2004 Mar, 35(2), 158 - 60
{Cloning the gene fragment coding the putative integrase-like protein from X maltophilia}; Liang SF et al.; OBJECTIVE: To amplify the nucleotide sequence of CG-like receptor from X anthomonas maltophilia(X maltophilia) . METHODS: Using the specific primer P1 designed by Grover's reported 342 bp partial nucleotide sequence of X maltophilia CG-like receptor and random primer to PCR amplify, PCR product was cloned in the pUCm-T vector . After the recombinant plasmid was tested by restriction endonuclease digestion, the insert on the recombinant plasmid was sequenced and analyzed . RESULTS: About 500 bp PCR product was cloned in the pUCm-T vector and obtained the recombinant pUCm-Int . By sequencing to the insert on the pUCm-Int with M13 universal sequencing primers, the 410-486 bp fragment of the cloned 510 bp nucleotide sequence (GenBank accession number: AY363962) showed 84% identity with the 9304-8958 bp fragment of the XACb0009 gene on plasmid pXAC64 of Xanthomonas axonopodis pv . citri . And the 4-166aa fragment of its translated 169aa sequence had 62% identity with the 38-200aa sequence of integrase-like protein coded by the XACb0009 gene . CONCLUSION: The cloned 510 bp nucleotide sequence was possibly the partial gene sequence coding the integrase-like protein of X maltophilia.

Curr Microbiol, 2004 May, 48(5), 354 - 9
The oligopeptide permease (Opp) of the plant pathogen Xanthomonas axonopodis pv . citri; Moutran A et al.; The oligopeptide permease (Opp), a protein-dependent ABC transporter, has been found in the genome of Xanthomonas axonopodis pv . citri ( Xac), but not in Xanthomonas campestris pv . campestris ( Xcc) . Sequence analysis indicated that 4 opp genes ( oppA, oppB, oppC, oppD/F), located in a 33.8-kbp DNA fragment present only in the Xac genome, are arranged in an operon-like structure and share highest sequence similarities with Streptomyces roseofulvus orthologs . Nonetheless, analyses of the GC content, codon usage, and transposon positioning suggested that the Xac opp operon does not have an exogenous origin . The presence of a stop codon at one of the ATP-binding domains of OppD/F would render the uptake system nonfunctional, but detection of a single polycistronic mRNA and periplasmic OppA in actively growing bacteria suggests that the Opp permease is active and could contribute to the distinct nutritional requirements and host specificities of the two Xanthomonas species.

J Bacteriol, 2004 Apr, 186(8), 2309 - 18
Characterization of the cis-acting regulatory element controlling HrpB-mediated activation of the type III secretion system and effector genes in Ralstonia solanacearum; Cunnac S et al.; The ability of Ralstonia solanacearum to cause disease on plants depends on its type III secretion system (TTSS) encoded by hrp genes . The expression of hrp genes and known TTSS substrates is coordinately regulated by HrpB, a member of the AraC family of transcriptional regulators . Two HrpB-regulated promoters (hrpY and popABC) were characterized by deletion analysis, and the HrpB-dependent activation of these promoters was found to be conferred by a 25-nucleotide DNA element, the hrp(II) box (TTCGn16TTCG), which is present in other hrp promoters . The hrp(II) box element is an imperfect plant inducible promoter box, an element which was originally found in hrp promoters of Xanthomonas campestris (S . Fenselau and U . Bonas, Mol . Plant-Microbe Interact . 8:845-854, 1995) but which was not characterized at the molecular level . Site-directed mutagenesis showed that the hrp(II) box is essential for hrpY promoter activation in vivo . Functional analysis of the hrp(II) box element identified critical parameters that are required for HrpB-dependent activity . Further mapping analyses of several other hrpB-dependent promoters also indicated that the position of the hrp(II) box is conserved, at -70 to -47 bp from the transcriptional start . As a first step toward identifying novel TTSS effectors, we used the hrp(II) box consensus sequence to search for potential HrpB-regulated promoters in the complete genome sequence of R . solanacearum strain GMI1000 . Among the 114 genes identified, a subset of promoters was found to have a structural relationship with hrp promoters, thus providing a pool of candidate genes encoding TTSS effectors.

Folia Microbiol (Praha), 2003, 48(6), 799 - 804
Characterization of two antagonistic strains of Rahnella aquatilis isolated from soil in Egypt; el-Hendawy HH et al.; In an attempt to obtain biological control agents for controlling bacterial spot of cucumber, over 250 bacterial strains were isolated from agricultural soil samples, collected from different localities in Giza Governorate (Egypt) and screened for in vitro antibiosis towards Xanthomonas campestris . Only 2 strains showed antagonistic activity . They and their culture filtrates restricted the growth of a number of G- and G(+)-indicator bacteria . On Chrome Azurol S agar, both strains exhibited a marked siderophore production . Biolog plates identified these strains as Rahnella aquatilis . Their characteristics were studied and compared with literature data on R . aquatilis . This antagonistic bacterium has not been previously isolated in Egypt.

Curr Microbiol, 2004 Apr, 48(4), 251 - 61
PilR enhances the sensitivity of Xanthomonas axonopodis pv . citri to the infection of filamentous bacteriophage Cf; Yang YC et al.; The pilA gene, which encodes the major structure of pili, is required for infection of Xanthomonas axonopodis pv . citri ( X . a . pv . citri) by the filamentous bacteriophage Cf . Two open reading frames (ORFs) located downstream of pilA were cloned and characterized . One 1392-bp ORF encodes a protein of 464 amino acids which shares substantial similarity with pilR of other bacterial species; the second ORF ( orf618), of 1854-bp, shares sequence similarity with pilS . The existence of the pilR-like and pilS-like genes in various X . campestris pathovars indicated that these two genes are well conserved in Xanthomonas . pilR and pilS mutants were constructed by gene replacement . We found that a pilR mutant, resistant to the infection of phage Cf, was unable to synthesize PilA protein; however, the abundance of the PilA protein and of the pilA transcript was markedly increased by the introduction of a plasmid containing the cloned pilR gene . The restoration of the normal pilus-specific sensitivity of this transformed clone to Cf indicated that the pilR gene functions as a transcriptional regulator of pilA . The pilS mutant, however, was susceptible to Cf infection, and the level of pilA expression in this mutant was similar to that of wild-type cells . Promoter analysis of luciferase reporter gene constructs containing the 5' untranslated regions of pilR or pilS genes revealed that, although the pilR and pilS are contiguous in X . a . pv . citri, the two genes are expressed independently, and the strong pilR promoter leads to the accumulation of PilR in X . a . pv . citri, which positively regulates the biosynthesis of PilA . These results revealed the enhanced sensitivity of X . a . pv . citri to phage Cf in the presence of PilR and indicated that the filamentous phage Cf utilize bacterial pili as a receptor site for its infection.

Mol Cells, 2004 Feb 29, 17(1), 144 - 50
Molecular characterization of a pathogenesis-related protein 8 gene encoding a class III chitinase in rice; Park CH et al.; A cDNA encoding a class III chitinase (Oschib1) was isolated from a cDNA library constructed from rice leaves infected with the blast fungus Magnaporthe grisea . The cDNA contains an open reading frame of 861 nucleotides encoding 286 amino acid residues with a pI of 5.06 . The deduced amino acid sequence of Oschibl has a high level of similarity with class IIIb chitinases of Gladiolus gandavensis (46%) and Tulipa bakeri (49%) . A high level of Oschibl mRNA was detected after inoculation with M . grisea or Xanthomonas oryzae pv . oryzae . Expression of Oschib1 was induced more rapidly when an avirulent strain of M . grisea was inoculated (incompatible interaction) than when a virulent strain was used (compatible interaction) . Expression of Oschibl was also induced by treatment of signaling molecules such as salicylic acid, ethylene, and methyl jasmonic acid, and by treatment with H2O2 or CuSO4 . The induction patterns of Oschibl expression suggest that Oschib1 may be involved in defense response against pathogen infections and may be classified as a member of pathogenesis-related protein 8 in rice.

BMC Evol Biol . 2004 Mar 24;4(1):10.
A plant natriuretic peptide-like gene in the bacterial pathogen Xanthomonas axonopodis may induce hyper-hydration in the plant host: a hypothesis of molecular mimicry; Nembaware V et al.; BACKGROUND: Plant natriuretic peptides (PNPs) are systemically mobile molecules that regulate homeostasis at nanomolar concentrations . PNPs are up-regulated under conditions of osmotic stress and PNP-dependent processes include changes in ion transport and increases of H2O uptake into protoplasts and whole tissue . PRESENTATION OF THE HYPOTHESIS: The bacterial citrus pathogen Xanthomonas axonopodis pv . Citri str . 306 contains a gene encoding a PNP-like protein . We hypothesise that this bacterial protein can alter plant cell homeostasis and thus is likely to represent an example of molecular mimicry that enables the pathogen to manipulate plant responses in order to bring about conditions favourable to the pathogen such as the induced plant tissue hyper-hydration seen in the wet edged lesions associated with Xanthomonas axonopodis infection . TESTING THE HYPOTHESIS: We found a Xanthomonas axonopodis PNP-like protein that shares significant sequence similarity and identical domain organisation with PNPs . We also observed a significant excess of conserved residues between the two proteins within the domain previously identified as being sufficient to induce biological activity . Structural modelling predicts identical six stranded double-psi beta barrel folds for both proteins thus supporting the hypothesis of similar modes of action . No significant similarity between the Xanthomonas axonopodis protein and other bacterial proteins from GenBank was found . Sequence similarity of the Xanthomonas axonopodis PNP-like protein with the Arabidopsis thaliana PNP (AtPNP-A), shared domain organisation and incongruent phylogeny suggest that the PNP-gene may have been acquired by the bacteria in an ancient lateral gene transfer event . Finally, activity of a recombinant Xanthomonas axonopodis protein in plant tissue and changes in symptoms induced by a Xanthomonas axonopodis mutant with a knocked-out PNP-like gene will be experimental proof of molecular mimicry . IMPLICATION OF THE HYPOTHESIS: If the hypothesis is true, it could at least in part explain why the citrus pathogen Xanthomonas campestris that does not contain a PNP-like gene produces dry corky lesions while the closely related Xanthomonas axonopodis forms lesions with wet edges . It also suggests that genes typically found in the host, horizontally transferred or heterologous, can help to explain aspects of the physiology of the host-pathogen interactions.

Mol Gen Mikrobiol Virusol, 2004, (1), 18 - 21
{Phytase activity in some groups of bacteria . Search for and cloning of genes for bacterial phytases}; Shedova EN et al.; A search for phytase genes in 9 Bacillus strains from the collection of IMGAN was implemented . The growth optimum of strains IX-22, IX-12B, K17-2, K18, IMG I, IMG II, M4 and M8 was 50-60 degrees C; the optimal growth temperature for Bacillus sp . 790 was 45-47 degrees C . According to the sequence data of 16S RNA genes, Bacillus sp . 790 belongs to the B . subtilis/amyloliquefaciens group . The other 8 strains were identified as B . licheniformis . Selection of Bacillus strains, potentially containing the phytase genes, was performed via PCR with primers designed on the basis of the conserved sequence regions of the phyA gene from B . amyloliquefaciens FZB45 with chromosomal DNA being used as the template . The nucleotide sequences of all PCR fragments showed a high level of homology to the known Bacillus phytase genes . The gene libraries of B . licheniformis M8 and B . amyloliquefaciens 790 in E . coli were constructed and phytase-containing clones were selected from them . Twenty-four Pseudomonas strains of different species, 5 Xanthomonas maltophilia strains and 1 Xanthomonas malvacearum (all from the mentioned collection) were tested for phytase activity . Such activity was found in 13 Pseudomonas strains and in 6 Xanthomonas strains . The accumulation of phytase in Pseudomonas was shown to take place at later (over 2 days') growth stages . The optimum pH for phytase from 3 Pseudomonas strains were established . The enzymes were found to be most active at pH 5.5.

Genetics, 2004 Feb, 166(2), 693 - 706
Effector genes of Xanthomonas axonopodis pv . vesicatoria promote transmission and enhance other fitness traits in the field; Wichmann G et al.; Establishing durable disease resistance in agricultural crops, where much of the plant defense is provided through effector-R gene interactions, is complicated by the ability of pathogens to overcome R gene resistance by losing the corresponding effector gene . Many proposed methods to maintain disease resistance in the field depend on the idea that effector gene loss results in a fitness cost to the pathogen . In this article we test for fitness costs of effector gene function loss . We created directed knockouts of up to four effector genes from the bacterial plant pathogen Xanthomonas axonopodis pv . vesicatoria (Xav) and examined the effect of the loss of a functional gene product on several important fitness parameters in the field . These traits included transmission, lesion development, and epiphytic survival . We found that the products of all four effector genes had significant and often additive effects on fitness traits . Additional greenhouse tests revealed costs of effector gene loss on in planta growth and further showed that the effects on lesion development were separable from the effects on growth . Observable fitness effects of the three plasmid-borne effector genes were dependent upon the loss of functional avrBs2, indicating that complex functional interactions exist among effector genes with Xav.

Annu Rev Phytopathol, 1998, 36, 41 - 58
Diversity among xanthomonads pathogenic on pepper and tomato; Jones JB et al.; Xanthomonas campestris pv . vesicatoria, causal agent of bacterial spot of tomato and pepper, had been considered for nearly 70 years to be a relatively homogeneous organism . However, in the past decade this bacterium was determined to be composed of two genetically and phenotypically distinct groups . The two groups, designated A and B, were distinguished based on amylolytic activity, expression of unique protein bands, reaction on differential hosts (tomato races T1 and T2), reaction patterns with monoclonal antibodies, DNA restriction profiles, and DNA:DNA hybridization . The A and B groups were placed into X . axonopodis pv . vesicatoria and X . vesicatoria, respectively . A third group, designated C, was pathogenically (race T3) and serologically distinct from A and B strains, and formed unique DNA restriction profiles . DNA:DNA hybridization data suggest that C is distinct but related to A strains and may represent a subspecies of A . A final group, designated D, consisted of X . gardneri, an organism identified in Yugoslavia in 1957, and also found in Costa Rica . Group D was determined to be genetically distinct from strains within the other two groups; it represents a third Xanthomonas species pathogenic on tomato and pepper.

Biotechnol Lett, 2004 Jan, 26(2), 171 - 5
In vitro mutagenesis of Xanthomonas campestris alpha-amylase gene by partially replacing deoxythymidine triphosphate with 5-bromo-2'-deoxyuridine-5'-triphosphate using a PCR technique; Ma XD et al.; Three mutants of the wild type alpha-amylase gene from Xanthomonas campestris pv . campestris 8004 were obtained using a PCR technique in which deoxythymidine triphosphate (dTTP) was partially replaced by 5-bromo-2'-deoxyuridine-5'-triphosphate (BrdUTP), at an optimal dTTP:BrdUTP ratio of 1000:1 . Of thre three mutants that were obtained and which were sequenced, one mutant with 40 times higher activity than the wild type alpha-amylase gene product was obtained by using primary PCR products as a template for a second PCR reaction.

Biochim Biophys Acta, 2004 Feb 20, 1676(3), 211 - 22
Identification of a novel pathogen-induced gene encoding a leucine-rich repeat protein expressed in phloem cells of Capsicum annuum; Jung EH et al.; The CALRR1 gene, expressed in pepper leaves following infection by Xanthomonas campestris pv . vesicatoria, encodes a secreted leucine-rich repeat (LRR) with five tandem repeats of a 24-amino-acid LRR motif . Northern blot analyses revealed that CALRR1 is not constitutively expressed in pepper plants, but is strongly induced upon the infection by X . campestris pv . vesicatoria, Phytophthora capsici, Colletotrichum coccodes and Colletotrichum gloeosporioides on leaves . CALRR1 was not systemically induced in upper leaves by bacterial infection . The inoculation of bacterial live cells, and treatment with dead cells and culture filtrates of pathogenic or nonpathogenic bacteria triggered the accumulation of CALRR1 transcripts . Treatment with signaling molecules, including salicylic acid (SA), ethylene (ET), methyl jasmonate (MeJA), dl-beta-amino-n-butyric acid (BABA) and benzothiadiazole (BTH), did not activate the transcription of the CALRR1 gene, indicating that CALRR1 expression is not regulated by defense signaling pathways activated by these molecules . CALRR1 was induced by treatment with high salinity, abscisic acid (ABA) and wounding, but not by drought and cold stress . An in situ hybridization study showed that CALRR1 mRNA was localized in phloem tissues of leaves, stems, and green fruits of pepper plants during the pathogen infection and ABA exposure . The location characteristics and the spatio-temporal expression pattern of CALRR1 suggest that it may play a role in protecting phloem cells against biotic and abiotic stresses affecting phloem function.

J Bacteriol, 2004 Mar, 186(5), 1374 - 80
Evidence for HrpXo-dependent expression of type II secretory proteins in Xanthomonas oryzae pv . oryzae; Furutani A et al.; Xanthomonas oryzae pv . oryzae is a causal agent of bacterial leaf blight of rice . Recently, an efficient hrp-inducing medium, XOM2, was established for this bacterium . In this medium, more than 10 proteins were secreted from the wild-type strain of X . oryzae pv . oryzae . Many of these proteins disappeared or decreased in amount in culture on XOM2 when incubated with the strain that has a mutation in the hrp regulatory gene . Interestingly, the secretory protein profile of a mutant lacking a type III secretion system (TTSS), components of which are encoded by hrp genes, was similar to that of the wild-type strain except that a few proteins had disappeared . This finding suggests that many HrpXo-dependent secretory proteins are secreted via systems other than the TTSS . By isolating mutant strains lacking a type II secretion system, we examined this hypothesis . As expected, many of the HrpXo-dependent secretory proteins disappeared or decreased when the mutant was cultured in XOM2 . By determining the N-terminal amino acid sequence, we identified one of the type II secretory proteins as a cysteine protease homolog, CysP2 . Nucleotide sequence analysis revealed that cysP2 has an imperfect plant-inducible-promoter box, a consensus sequence which HrpXo regulons possess in the promoter region, and a deduced signal peptide sequence at the N terminus . By reverse transcription-PCR analysis and examination of the expression of CysP2 by using a plasmid harboring a cysP2::gus fusion gene, HrpXo-dependent expression of CysP2 was confirmed . Here, we reveal that the hrp regulatory gene hrpXo is also involved in the expression of not only hrp genes and type III secretory proteins but also some type II secretory proteins.

Mol Plant Microbe Interact, 2004 Feb, 17(2), 140 - 51
Overexpression of (At)NPR1 in rice leads to a BTH- and environment-induced lesion-mimic/cell death phenotype; Fitzgerald HA et al.; Systemic acquired resistance (SAR) is an inducible defense response that protects plants against a broad spectrum of pathogens . A central regulator of SAR in Arabidopsis is NPR1 (nonexpresser of pathogenesis-related genes) . In rice, overexpression of Arabidopsis NPR1 enhances plant resistance to the bacterial pathogen Xanthomonas oryzae pv . oryzae . This report demonstrates that overexpression of (At)NPR1 in rice also triggers a lesion-mimic/cell death (LMD) phenotype . The LMD phenotype is environmentally regulated and heritable . In addition, the development of lesions and death correlates with the expression of rice defense genes and the accumulation of hydrogen peroxide . Application of the salicylic acid (SA) analog, benzo(1,2,3) thiadiazole-7-carbothioc acid S-methyl ester (BTH), potentiates this phenotype Endogenous SA levels are reduced in rice overexpressing (At)NPR1 when compared with wildtype plants, supporting the idea that (At)NPR1 may perceive and modulate the accumulation of SA . The association of (At)NPR1 expression in rice with the development of an LMD phenotype suggests that (At)NPR1 has multiple roles in plant stress responses that may affect its efficacy as a transgenic tool for engineering broad-spectrum resistance.

Plant J, 2004 Feb, 37(4), 517 - 27
Xa26, a gene conferring resistance to Xanthomonas oryzae pv . oryzae in rice, encodes an LRR receptor kinase-like protein; Sun X et al.; Rice bacterial blight, caused by Xanthomonas oryzae pv . oryzae (Xoo), is one of the most serious rice diseases worldwide . A rice gene, Xa26, conferring resistance against Xoo at both seedling and adult stages was isolated by map-based cloning strategies from the rice cultivar Minghui 63 . Xa26 belongs to a multigene family consisting of four members . It encodes a leucine-rich repeat (LRR) receptor kinase-like protein and is constitutively expressed . Sequence analysis revealed that IRBB3 and Zhachanglong lines that are resistant to a broad range of Xoo strains, also carry Xa26 . However, significant difference in lesion length was observed among these lines after inoculation with a set of Xoo strains . Moreover, transgenic plants carrying Xa26 showed enhanced resistance compared with the donor line of the gene in both seedling and adult stages . These results suggest that the resistance conferred by Xa26 is influenced by the genetic background.

Funct Integr Genomics, 2004 Jul, 4(3), 196 - 205 Epub 2004 Feb 04.
EST and microarray analyses of pathogen-responsive genes in hot pepper ( Capsicum annuum L.) non-host resistance against soybean pustule pathogen ( Xanthomonas axonopodis pv . glycines); Lee S et al.; Large-scale single-pass sequencing of cDNA libraries and microarray analysis have proven to be useful tools for discovering new genes and studying gene expression . As a first step in elucidating the defense mechanisms in hot pepper plants, a total of 8,525 expressed sequence tags (ESTs) were generated and analyzed in silico . The cDNA microarray analysis identified 613 hot pepper genes that were transcriptionally responsive to the non-host soybean pustule pathogen Xanthomonas axonopodis pv . glycines ( Xag) . Several functional types of genes, including those involved in cell wall modification/biosynthesis, transport, signaling pathways and divergent defense reactions, were induced at the early stage of Xag infiltration . In contrast, genes encoding proteins that are involved in photosynthesis, carbohydrate metabolism and the synthesis of chloroplast biogenetic proteins were down-regulated at the late stage of Xag infiltration . These expression profiles share common features with the expression profiles elicited by other stresses, such as fungal challenge, wounding, cold, drought and high salinity . However, we also identified several novel transcription factors that may be specifically involved in the defense reaction of the hot pepper . We also found that the defense reaction of the hot pepper may involve the deactivation of gibberellin . Furthermore, many genes encoding proteins with unknown function were identified . Functional analysis of these genes may broaden our understanding of non-host resistance . This study is the first report of large-scale sequencing and non-host defense transcriptome analysis of the hot pepper plant species . (The sequence data in this paper have been submitted to the dbEST and GenBank database under the codes 10227604-10236595 and BM059564-BM068555, respectively . Additional information is available at http://plant.pdrc.re.kr/ks200201/pepper.html).

Int J Syst Evol Microbiol, 2004 Jan, 54(Pt 1), 15 - 24
Polyphasic characterization of xanthomonads isolated from onion, garlic and Welsh onion (Allium spp.) and their relatedness to different Xanthomonas species; Roumagnac P et al.; Bacterial blight is an emerging disease that affects primarily onion, but also garlic and Welsh onion . The present study was undertaken to characterize the causative xanthomonad(s) by a polyphasic approach using a worldwide collection of 33 bacterial strains . Analysis of 16S rRNA gene sequence similarities indicated that the causal agent belongs to the campestris core in the genus Xanthomonas, which is in agreement with results of phenotypic characterization (analyses of carbon source utilization and fatty acid methyl esters) . However, DNA-DNA hybridization, thermal stability of DNA reassociation and fluorescent amplified fragment length polymorphism analysis allowed the causal agent to be identified as a pathovar of Xanthomonas axonopodis.

J Biol Chem, 2004 Apr 9, 279(15), 14819 - 27 Epub 2004 Jan 23.
LeMPK3 is a mitogen-activated protein kinase with dual specificity induced during tomato defense and wounding responses; Mayrose M et al.; Mitogen-activated protein (MAP) kinase cascades are readily activated during the response of plants to avirulent pathogens or to pathogen-derived elicitors . Here we show that the tomato MAP kinase LeMPK3 is specifically induced at the mRNA level during elicitation of the hypersensitive response in resistant plants infected by avirulent strains of the phytopathogenic bacteria Xanthomonas campestris pv . vesicatoria and Pseudomonas syringae pv . tomato, as well as upon treatment with the fungal elicitor ethylene-inducing xylanase . LeMPK3 gene expression was also induced very rapidly by mechanical stress and wounding much earlier than upon pathogen infection, but not in response to the defense-related plant hormones ethylene and jasmonic acid . Moreover, in resistant tomato plants infected by X . campestris pv . vesicatoria, transcript accumulation was followed by an increase in LeMPK3 kinase activity . Biochemical characterization of a glutathione S-transferase-LeMPK3 fusion protein revealed that the LeMPK3 MAP kinase autophosphorylates in vitro mainly on tyrosine and less so on threonine and serine, whereas it phosphorylates myelin basic protein on serine and threonine . In vitro phosphorylation of a poly-(Glu-Tyr) copolymer by LeMPK3 demonstrated its capability to phosphorylate tyrosine residues on substrates as well . By mutagenesis and phosphoamino acid analysis, Tyr-201 in the kinase activation domain was identified as the main LeMPK3 autophosphorylation site and as critical for kinase activity . Finally, LeMPK3 autophosphorylation showed a preference for Mn(2+) cations and proceeded via an intramolecular mechanism with an estimated K(m) value for ATP of 9.5 microm . These results define LeMPK3 as a MAP kinase with dual specificity and strongly suggest that it represents a convergence point for different signaling pathways inducing the activation of defense responses in tomato.

Glycobiology, 2004 Mar, 14(3), 233 - 41 Epub 2004 Jan 21.
Functional characterization of GumK, a membrane-associated beta-glucuronosyltransferase from Xanthomonas campestris required for xanthan polysaccharide synthesis; Barreras M et al.; Xanthomonas campestris is a Gram-negative bacterium that produces an exopolysaccharide known as xanthan gum . Xanthan is involved in a variety of biological functions, including pathogenesis, and is widely used in the industry as thickener and viscosifier . Although the genetics and biosynthetic process of xanthan are well documented, the enzymatic components have not been examined and no data on glycosyltransferases have been reported . We describe the functional characterization of the gumK gene product, an essential protein for xanthan synthesis . Immunoblots and complementation studies showed that GumK is a 44-kDa protein associated to the membrane fraction . This value corresponds to the expected molecular mass for GumK encoded by an extended open reading frame than proposed from previous genetic data and in X . campestris published complete genome . The protein was expressed in Escherichia coli cells . The purified protein catalyzed the transfer of a glucuronic acid residue from UDP-glucuronic acid to mannose-alpha-1,3-glucose-beta-1,4-glucose-P-P-polyisoprenyl with formation of a glucuronic acid-beta-mannose linkage . We examined the acceptor substrate specificity . GumK was unable to use the trisaccharide acceptor freed from the pyrophosphate lipid moiety . Replacement of the natural lipid moiety by phytanyl showed that the catalytic function could proceed with glucuronic acid transfer . These results suggest the enzyme does not show specificity for the lipidic portion of the acceptor . GumK showed diminished activity when tested with 6-O-acetyl-mannose-alpha-1,3-glucose-beta-1,4-glucose-P-P-polyisoprenyl, a putative intermediate in the synthesis of xanthan . This could indicate that acetylation of the internal mannose takes place after the formation of the GumK product.

Mol Microbiol, 2004 Feb, 51(3), 903 - 12
A bacterial cell-cell communication signal with cross-kingdom structural analogues; Wang LH et al.; Extracellular signals are the key components of microbial cell-cell communication systems . This report identified a diffusible signal factor (DSF), which regulates virulence in Xanthomonas campestris pv . campestris, as cis-11-methyl-2-dodecenoic acid, an alpha,beta unsaturated fatty acid . Analysis of DSF derivatives established the double bond at the alpha,beta positions as the most important structural feature for DSF biological activity . A range of bacterial pathogens, including several Mycobacterium species, also displayed DSF-like activity . Furthermore, DSF is structurally and functionally related to farnesoic acid (FA), which regulates morphological transition and virulence by Candida albicans, a fungal pathogen . Similar to FA, which is also an alpha,beta unsaturated fatty acid, DSF inhibits the dimorphic transition of C . albicans at a physiologically relevant concentration . We conclude that alpha,beta unsaturated fatty acids represent a new class of extracellular signals for bacterial and fungal cell-cell communications . As prokaryote-eukaryote interactions are ubiquitous, such cross-kingdom conservation in cell-cell communication systems might have significant ecological and economic importance.

Appl Environ Microbiol, 2004 Jan, 70(1), 255 - 61
Genetic structure and population dynamics of Xanthomonas axonopodis pv . manihotis in Colombia from 1995 to 1999; Restrepo S et al.; Restriction fragment length polymorphisms (RFLPs) were used to study the population genetics and temporal dynamics of the cassava bacterial pathogen Xanthomonas axonopodis pv . manihotis . The population dynamics were addressed by comparing samples collected from 1995 to 1999 from six locations, spanning four different edaphoclimatic zones (ECZs) . Forty-five different X . axonopodis pv . manihotis RFLP types or haplotypes were identified between 1995 and 1999 . High genetic diversity of the X . axonopodis pv . manihotis strains was evident within most of the fields sampled . In all but one site, diversity decreased over time within fields . Haplotype frequencies significantly differed over the years in all but one location . Studies of the rate of change of X . axonopodis pv . manihotis populations during the cropping cycle in two sites showed significant changes in the haplotype frequencies but not composition . However, variations in pathotype composition were observed from one year to the next at a single site in ECZs 1 and 2 and new pathotypes were described after 1997 in these ECZs, thus revealing the dramatic change in the pathogen population structure of X . axonopodis pv . manihotis . Disease incidence was used to show the progress of cassava bacterial blight in Colombia during the 5-year period in different ecosystems . Low disease incidence values were correlated with low rainfall in 1997 in ECZ 1.

J Bacteriol, 2004 Jan, 186(2), 411 - 8
Molecular and functional characterization of a unique sucrose hydrolase from Xanthomonas axonopodis pv . glycines; Kim HS et al.; A novel sucrose hydrolase (SUH) from Xanthomonas axonopodis pv . glycines, a causative agent of bacterial pustule disease on soybeans, was studied at the functional and molecular levels . SUH was shown to act rather specifically on sucrose (K(m) = 2.5 mM) but not on sucrose-6-phosphate . Protein analysis of purified SUH revealed that, in this monomeric enzyme with an estimated molecular mass of 70,223 +/- 12 Da, amino acid sequences determined for several segments have corresponding nucleotide sequences in XAC3490, a protein-coding gene found in the genome of X . axonopodis pv . citri . Based on this information, the SUH gene, consisting of an open reading frame of 1,935 bp, was cloned by screening a genomic library of X . axonopodis pv . glycines 8ra . Database searches and sequence comparison revealed that SUH has significant homology to some family 13 enzymes, with all of the crucial invariant residues involved in the catalytic mechanism conserved, but it shows no similarity to known invertases belonging to family 32 . suh expression in X . axonopodis pv . glycines requires sucrose induction, and insertional mutagenesis resulted in an absence of sucrose-inducible sucrose hydrolase activity in crude protein extracts and a sucrose-negative phenotype . Recombinant SUH, overproduced in Escherichia coli and purified, was shown to have the same enzymatic characteristics in terms of kinetic parameters.

Antimicrob Agents Chemother, 2004 Jan, 48(1), 209 - 15
Constitutive expression of a chromosomal class A (BJM group 2) beta-lactamase in Xanthomonas campestris; Weng SF et al.; Sequencing of the upstream region of the beta-lactamase gene from Xanthomonas campestris pv . campestris 11 (bla(XCC-1)) revealed the cognate ampR1 gene (289 amino acids, 31 kDa) . It runs divergently from bla(XCC-1) with a 100-bp intergenic region (IG) containing partially overlapped promoters with structural features typical of the bla-ampR IG . The deduced AmpR1 protein shows significant identity in amino acid sequence and conserved motifs with AmpR proteins of other species, e.g., of Pseudomonas aeruginosa (58.2% amino acid identity) . Results of insertional mutation, complementation tests, and beta-lactamase assays suggested that expression of bla(XCC-1) was constitutive and dependent on AmpR1 . Four bla genes and two ampR genes are present in the fully sequenced X . campestris pv . campestris ATCC 33913 genome, with XCC3039 and XCC3040 considered the analogues of bla(XCC-1) and ampR1, respectively . An ampR1 homologue was detected by Southern hybridization in the ampicillin-resistant Xanthomonas strains, which appear to express beta-lactamase constitutively . Although the significance remains to be studied, constitutive expression of beta-lactamase by a widespread bacterial genus raises environmental concerns regarding the dissemination of resistance genes.

Plant J, 2004 Jan, 37(2), 186 - 98
Pathogenesis-related protein 10 isolated from hot pepper functions as a ribonuclease in an antiviral pathway; Park CJ et al.; A hot pepper (Capsicum annuum) cDNA clone encoding pathogenesis-related protein 10 (CaPR-10) was isolated by differential screening of a cDNA library prepared from pepper leaves inoculated with tobacco mosaic virus pathotype (TMV-P0) . CaPR-10 transcripts were induced in the incompatible interaction with TMV-P0 or Xanthomonas campestris pv . vesicatoria (Xcv) but not induced in the compatible interaction . Characterization of enzymatic properties of CaPR-10 indicated that the recombinant protein exhibits a ribonucleolytic activity against TMV RNA, as well as against pepper total RNA, and shows its putative antiviral activity in several conditions . The CaPR-10 protein existed at very low level in leaf tissue but was dramatically induced as soon as plants were inoculated with TMV-P0, and this was correlated with the increase of its ribonucleolytic activity . Immunoblot analysis and pull-down assays using proteins extracted from pepper leaves showed that TMV-P0 inoculation led to the phosphorylation of CaPR-10, a modification that should affect its capacity for RNase function . We present data that the induction and subsequent phosphorylation of CaPR-10 increased its ribonucleolytic activity to cleave invading viral RNAs, and this activity should be important to its antiviral pathway during viral attack in vivo.

Acta Crystallogr D Biol Crystallogr, 2004 Jan, 60(Pt 1), 129 - 31 Epub 2003 Dec 18.
Crystallization and preliminary X-ray crystallographic analysis of the N-terminal domain of XpsE protein from Xanthomonas campestris, an essential component of the type II protein-secretion machinery; Chen Y et al.; Secretion of pre-folded extracellular proteins across the outer membrane of Gram-negative bacteria is mainly assisted by the type II secretion machinery composed of 12-15 proteins . Here, the crystallization and preliminary analysis of one of the essential components of Xanthomonas campestris secretion machinery, the 21 kDa N-terminal domain of XpsE protein (XpsE(N)), are reported . XpsE(N) has been crystallized at 277 K using PEG 400 as precipitant . These crystals belong to the tetragonal space group P4(1)2(1)2 (or P4(3)2(1)2), with unit-cell parameters a = b = 56.1, c = 102.7 A . A 98.5% complete native data set from a frozen crystal has been collected to 2.0 A resolution at 100 K with an overall R(merge) of 5.0% . The presence of one subunit of XpsE(N) per asymmetric unit gives a crystal volume per protein weight (V(M)) of 1.92 A(3) Da(-1) and a solvent content of 36.1%.

Curr Microbiol, 2003 Nov, 47(5), 400 - 3
A simple method for in vivo expression studies of Xanthomonas axonopodis pv . citri; Mehta A et al.; A major problem in studying bacterial plant pathogens is obtaining the microorganism directly from the plant tissue to perform in vivo expression (protein or mRNA) analyses . Here we report an easy and fast protocol to isolate Xanthomonas axonopodis pv . citri directly from the host plant, in sufficient amounts to perform protein fingerprinting by 2-D gel electrophoresis as well as RNA expression assays . The protein profile obtained was very similar to that of X . axonopodis pv . citri grown in the presence of a leaf extract of Citrus sinensis; however, some differential proteins expressed in vivo were observed . Total RNA extraction revealed typical 16S and 23S bands in the agarose gel, and RT-PCR reactions using primers specific for genes of the bacterium confirmed the quality of the RNA preparation . Also, RT-PCR reactions using plant ribosomal primers were employed, and no amplification product was obtained, indicating that plant RNA is not present in the bacterium RNA sample.

Carbohydr Res, 2004 Jan 2, 339(1), 157 - 60
Structure of the O-polysaccharide of Xanthomonas cassavae GSPB 2437; Senchenkova SN et al.; The following structure of the O-polysaccharide of the phytopathogenic bacterium Xanthomonas cassavae GSPB 2437 was determined by sugar analysis along with 1H and 13C NMR spectroscopy: {structure: see text}.

J Biochem Mol Biol, 2003 Nov 30, 36(6), 603 - 7
Resistance function of rice lipid transfer protein LTP110; Ge X et al.; Plant lipid transfer proteins (LTPs) are a class of proteins whose functions are still unknown . Some are proposed to have antimicrobial activities . To understand whether LTP110, a rice LTP that we previously identified from rice leaves, plays a role in the protection function against some serious rice pathogens, we investigated the antifungal and antibacterial properties of LTP110 . A cDNA sequence, encoding the mature peptide of LTP110, was cloned into the Impact-CN prokaryotic expression system . The purified protein was used for an in vitro inhibition test against rice pathogens, Pyricularia oryzae and Xanthomonas oryzae . The results showed that LTP110 inhibited the germination of Pyricularia oryzae spores, and its inhibitory activity decreased in the presence of a divalent cation . This suggests that the antifungal activity is affected by ions in the media; LTP110 only slightly inhibited the growth of Xanthomonas oryzae . However, the addition of LTP110 to cultured Chinese hamster ovarian cells did not retard growth, suggesting that the toxicity of LTP110 is only restricted to some cell types . Its antimicrobial activity is potentially due to interactions between LTP and microbe-specific structures.

J Biotechnol, 2003 Dec 19, 106(2-3), 203 - 14
Genomic approaches in Xanthomonas campestris pv . vesicatoria allow fishing for virulence genes; Buttner D et al.; Xanthomonas campestris pv . vesicatoria is an economically important pathogen of pepper and tomato and has been established as a model organism to study bacterial infection strategies . In the last two decades, intensive genetic and molecular analyses led to the isolation of many genes that play a role in the intimate molecular relationship with the host plant . Essential for pathogenicity is a type III protein secretion system, which delivers bacterial effector proteins into the host cell . Currently, the genome of X . campestris pv . vesicatoria is being sequenced . The availability of genomic sequence information will pave the way for the identification of new bacterial virulence factors by bioinformatic approaches . In this article, we will present preliminary data from the genomic sequence analysis and describe recent and novel studies to identify bacterial type III effector genes.

J Biotechnol, 2003 Dec 19, 106(2-3), 193 - 202
Comparison of two Xanthomonas campestris pathovar campestris genomes revealed differences in their gene composition; Vorholter FJ et al.; For the Xanthomonas campestris pathovar campestris wild-type strain B100 a plasmid-based clone library was constructed . The plasmids carried chromosomal fragments of 3-4 kb in size that were tagged in vitro with the artificial transposon KAN-2 . More than 3000 of the transposon target sites were characterized by DNA sequencing . The sequences obtained were compared to the recently published genome of Xanthomonas campestris pathovar campestris strain ATCC 33913 . Most of the sequenced clones derived from strain B100 matched the chromosomal sequence of strain ATCC 33913 . An alignment to the circular map of this chromosome revealed that the similarities were statistically distributed over the entire genome of strain ATCC 33913 . The similarity was obvious for protein coding sequences, as well as for mobile genetic elements . However, four regions in the genome of Xanthomonas campestris pathovar campestris strain ATCC 33913, ranging in size from 11 to 37 kb, were not represented in the sequenced clone library of Xanthomonas campestris pathovar campestris strain B100 . On the other hand, 1.2% of the sequenced clones originating from Xanthomonas campestris pathovar campestris strain B100 showed no or insignificant similarities to the genome of strain ATCC 33913.

J Biotechnol, 2003 Dec 19, 106(2-3), 121 - 33
Whole genome shotgun sequencing guided by bioinformatics pipelines--an optimized approach for an established technique; Kaiser O et al.; While the sequencing of bacterial genomes has become a routine procedure at major sequencing centers, there are still a number of genome projects at small- or medium-size facilities . For these facilities a maximum of control over sequencing, assembling and finishing is essential . At the same time, facilities have to be able to co-operate at minimum costs for the overall project . We have established a pipeline for the distributed sequencing of Alcanivorax borkumensis SK2, Azoarcus sp . BH72, Clavibacter michiganensis subsp . michiganensis NCPPB382, Sorangium cellulosum So ce56 and Xanthomonas campestris pv . vesicatoria 85-10 . Our pipeline relies on standard tools (e.g . PHRED/PHRAP, CAP3 and Consed/Autofinish) wherever possible, supplementing them with new tools (BioMake and BACCardI) to achieve the aims described above.

Mol Microbiol, 2004 Jan, 51(1), 89 - 96
Recognition of individual genes in a single bacterial cell by fluorescence in situ hybridization--RING-FISH; Zwirglmaier K et al.; Fluorescence in situ hybridization (FISH) using rRNA targeted oligonucleotide probes is a standard method for identification of microorganisms in environmental samples . Apart from its value as a phylogenetic marker ribosomal RNA has always been the favoured target molecule for FISH because of its abundance in all cells, whereas plasmids and DNA were regarded as unsuitable targets because of their low copy number . Here we present an improved FISH technique, which is based on polynucleotide probes . It goes beyond the detection of high copy intracellular nucleic acids such as rRNA (up to 10(4)-10(5) copies per cell) and allows for the first time the in situ detection of individual genes or gene fragments on plasmids (10(1)-10(3) copies per cell) and chromosomal DNA (<10 copies per cell) in a single cell . Using E . coli as model organism we were able to detect in situ cells harbouring the antibiotic resistance gene beta lactamase on high, medium and low copy plasmids as well as the chromosomal encoded housekeeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH) . Furthermore, we detected the prepilin peptidase gene xpsO in the plant pathogen Xanthomonas campestris in situ . Because of the characteristic hybridization signal obtained with this method--a halo-like, ring-shaped concentration of fluorescence in the cell periphery--we coined the term RING-FISH (recognition of individual genes) to differentiate it from conventional FISH.

J Bacteriol, 2003 Dec, 185(24), 7092 - 102
XopC and XopJ, two novel type III effector proteins from Xanthomonas campestris pv . vesicatoria; Noel L et al.; Pathogenicity of the gram-negative plant pathogen Xanthomonas campestris pv . vesicatoria depends on a type III secretion (TTS) system which translocates bacterial effector proteins into the plant cell . Previous transcriptome analysis identified a genome-wide regulon of putative virulence genes that are coexpressed with the TTS system . In this study, we characterized two of these genes, xopC and xopJ . Both genes encode Xanthomonas outer proteins (Xops) that were shown to be secreted by the TTS system . In addition, type III-dependent translocation of both proteins into the plant cell was demonstrated using the AvrBs3 effector domain as a reporter . XopJ belongs to the AvrRxv/YopJ family of effector proteins from plant and animal pathogenic bacteria . By contrast, XopC does not share significant homology to proteins in the database . Sequence analysis revealed that the xopC locus contains several features that are reminiscent of pathogenicity islands . Interestingly, the xopC region is flanked by 62-bp inverted repeats that are also associated with members of the Xanthomonas avrBs3 effector family . Besides xopC, a second gene of the locus, designated hpaJ, was shown to be coexpressed with the TTS system . hpaJ encodes a protein with similarity to transglycosylases and to the Pseudomonas syringae pv . maculicola protein HopPmaG . HpaJ secretion and translocation by the X . campestris pv . vesicatoria TTS system was not detectable, which is consistent with its predicted Sec signal and a putative function as transglycosylase in the bacterial periplasm.

Mol Plant Microbe Interact, 2003 Nov, 16(11), 1030 - 8
Activity of class III peroxidases in the defense of cotton to bacterial blight; Delannoy E et al.; Cotton cotyledons displayed a hypersensitive reaction (HR) in the cultivar Reba B50 after infiltration with the avirulent race 18 from Xanthomonas campestris pv . malvacearum . Two sets of peroxidases were associated with the HR time course . Early but transient accumulation of peroxidase in material encapsulating the bacteria in intercellular areas was observed by immunocytochemistry at 3 h postinfection and coincided with the oxidative burst . Total guaiacol-peroxidase activity was highly increased in cells undergoing HR, from 12 h after treatment . Molecular characterization of seven cloned peroxidase genes revealed highly conserved B, D, and F domains, with similarities to plant class III peroxidases . Analysis of gene expression showed variation in transcript accumulation during both compatible (race 20) and incompatible interactions for four of these genes: pod2, pod3, pod4, and pod6 . Pod4 and pod6 were more intensely up-regulated during resistance than during disease and in the control, while pod3 was specifically down-regulated during the HR after the oxidative burst . Pod2 was induced by pathogen infection and weakly stimulated in the control . These data suggest that cotton peroxidases may have various functions in the defense response to Xanthomonas infections.

Mol Plant Microbe Interact, 2003 Nov, 16(11), 973 - 82
PhyA, a secreted protein of Xanthomonas oryzae pv . oryzae, is required for optimum virulence and growth on phytic acid as a sole phosphate source; Chatterjee S et al.; Xanthomonas oryzae pv . oryzae causes bacterial leaf blight, a serious disease of rice . We have identified a novel virulence deficient mutant (BXO1691) of X . oryzae pv . oryzae that has a Tn5 insertion in an open reading frame (phyA; putative phytase A) encoding a 373-amino acid (aa) protein containing a 28-aa predicted signal peptide . Extracellular protein profiles revealed that a 38-kDa band is absent in phyA mutants as compared with phyA+ strains . A BLAST search with phyA and its deduced polypeptide sequence indicated significant similarity with conserved hypothetical proteins in Xanthomonas axonopodis pv . citri and Xanthomonas campestris pv . campestris and limited homology to secreted phytases of Bacillus species . Homology modeling with a Bacillus phytase as the template suggests that the PhyA protein has a similar six-bladed beta-propeller architecture and exhibits conservation of certain critical active site residues . Phytases are enzymes that are involved in degradation of phytic acid (inositol hexaphosphate), a stored form of phosphate in plants . The phyA mutants exhibit a growth deficiency in media containing phytic acid as a sole phosphate source . Exogenous phosphate supplementation promotes migration of phyA X . oryzae pv . oryzae mutants in rice leaves . These results suggest that the virulence deficiency of phyA mutants is, at least in part, due to inability to use host phytic acid as a source of phosphate . phyA-like genes have not been previously reported to be involved in the virulence of any plant pathogenic bacterium.

Curr Microbiol, 2003 Sep, 47(3), 260 - 2
Cadmium-induced adaptive resistance and cross-resistance to zinc in Xanthomonas campestris; Banjerdkij P et al.; Cadmium (Cd) and zinc (Zn) are environmental pollutants affecting both soil and water . The toxicity resulting from the exposure of Xanthomonas campestris, a soil bacterium and plant pathogen, to these metals was investigated . Pretreatment of X . campestris with sub-lethal concentrations of Cd induced adaptive protection against subsequent exposure to lethal doses of Cd . Moreover, Cd-induced cells also showed cross-resistance to lethal concentrations of Zn . These induced protections required newly synthesized proteins . Unexpectedly, Zn-induced cells did not exhibit adaptive protection against lethal concentrations of Zn or Cd . These data suggested that the increased resistance to Cd and Zn killing probably involved other protective mechanisms in addition to ion efflux.

Plant Physiol, 2003 Nov, 133(3), 1181 - 9 Epub 2003 Oct 09.
Multiple hormones act sequentially to mediate a susceptible tomato pathogen defense response; O'Donnell PJ et al.; Phytohormones regulate plant responses to a wide range of biotic and abiotic stresses . How a limited number of hormones differentially mediate individual stress responses is not understood . We have used one such response, the compatible interaction of tomato (Lycopersicon esculentum) and Xanthomonas campestris pv vesicatoria (Xcv), to examine the interactions of jasmonic acid (JA), ethylene, and salicylic acid (SA) . The role of JA was assessed using an antisense allene oxide cyclase transgenic line and the def1 mutant to suppress Xcv-induced biosynthesis of jasmonates . Xcv growth was limited in these lines as was subsequent disease symptom development . No increase in JA was detected before the onset of terminal necrosis . The lack of a detectable increase in JA may indicate that an oxylipin other than JA regulates basal resistance and symptom proliferation . Alternatively, there may be an increase in sensitivity to JA or related compounds following infection . Hormone measurements showed that the oxylipin signal must precede subsequent increases in ethylene and SA accumulation . Tomato thus actively regulates the Xcv-induced disease response via the sequential action of at least three hormones, promoting expansive cell death of its own tissue . This sequential action of jasmonate, ethylene, and SA in disease symptom development is different from the hormone interactions observed in many other plant-pathogen interactions.

Biotechnol Adv, 1999 Nov, 17(6), 489 - 508
The molecular genetics of virulence of Xanthomonas campestris; Chan JW et al.; Bacteria belonging to the genus Xanthomonas are important pathogens of many plants, and their virulence appears to be due primarily to secreted and surface compounds that could increase host nutrient loss, or avoid or suppress unfavorable conditions in the host . Type II and III secretory pathways are essential for virulence . Some individual extracellular enzymes (type II-secretion dependent) affect final bacterial population levels, whereas some avirulence gene products (type III-secretion dependent) affect virulence by altering host metabolism . Avr proteins, probably secreted via a pilus, can also be recognized by host resistance gene products . Virulence is also associated with bacterial surface polysaccharides, which may help to avoid host defense responses, and regulatory gene systems, which can control virulence gene expression.

Biotechnol Adv, 2000 Nov 1, 18(7), 549 - 79
Xanthan gum: production, recovery, and properties; Garcia-Ochoa F et al.; Xanthan gum is a microbial polysaccharide of great commercial significance . This review focuses on various aspects of xanthan production, including the producing organism Xanthomonas campestris, the kinetics of growth and production, the downstream recovery of the polysaccharide, and the solution properties of xanthan.

Biotechnol Adv, 2002 Apr, 20(1), 33 - 47
DNA markers and marker-assisted breeding for durable resistance to bacterial blight disease in rice; Rao KK et al.; Bacterial leaf blight caused by the bacterial pathogen Xanthomonas oryzae pv oryzae (Xoo) limits rice yield in all major rice-growing regions of the world, especially in irrigated lowland and rainfed conditions where predisposition factors favor disease development to epidemic proportions . Since bacterial pathogens are difficult to manage, development of host plant resistance is the most effective means of disease management . As many as 24 major genes conferring resistance to various races of the pathogen have been identified and utilized in rice breeding programs . However, large-scale and long-term cultivation of varieties carrying a single gene for resistance resulted in a significant shift in pathogen race frequency with consequent breakdown of resistance in these cultivars . To combat the problem of resistance breakdown, pyramiding of resistance genes into different cultivars is being carried out . Pyramiding of resistance genes is now possible with molecular markers that are developed for individual genes . This review discusses the various bacterial blight resistance genes identified and their corresponding molecular markers developed for breeding durable resistance into modern rice cultivars.

FEBS Lett, 2003 Sep 25, 552(2-3), 207 - 13
High-throughput screening of structural proteomics targets using NMR; Galvao-Botton LM et al.; We applied a high-throughput strategy for the screening of targets for structural proteomics of Xanthomonas axonopodis pv citri . This strategy is based on the rapid (1)H-(15)N HSQC NMR analysis of bacterial lysates containing selectively (15)N-labelled heterologous proteins . Our analysis permitted us to classify the 19 soluble candidates in terms of 'foldedness', that is, the extent to which they present a well-folded solution structure, as reflected by the quality of their NMR spectra . This classification allowed us to define a priority list to be used as a guide to select protein candidates for further structural studies.

Mikrobiologiia, 2003 Jul-Aug, 72(4), 498 - 502
{The extracellular proteases of the phytopathogenic bacterium Xanthomonas campestris}; Kalashnikova EE et al.; The culture liquids of three Xanthomonas campestris pv . campestris strains were found to possess proteolytic activity . The culture liquid of strain B-611 with the highest proteolytic activity was fractionated by salting-out with ammonium sulfate, gel filtration, and ion-exchange chromatography . The electrophoretic analysis of active fractions showed the presence of two proteases in the culture liquid of strain B-611, the major of which being serine protease . The treatment of cabbage seedlings with the proteases augmented the activity of peroxidase in the cabbage roots by 28%.

Theor Appl Genet, 2004 Feb, 108(3), 379 - 84 Epub 2003 Oct 02.
Isolation and characterization of rice mutants compromised in Xa21-mediated resistance to X . oryzae pv . oryzae; Wang GL et al.; The rice gene, Xa21, confers resistance to diverse races of Xanthomonas oryzae pv . oryzae (Xoo) and encodes a receptor-like kinase with leucine-rich repeats in the extra-cellular domain . To identify genes essential for the function of the Xa21 gene, 4,500 IRBB21 ( Xa21 isogenic line in IR24 background) mutants, induced by diepoxybutane and fast neutrons, were screened against Philippine race six (PR6) Xoo for a change from resistance to susceptibility . From two greenhouse screens, 23 mutants were identified that had changed from resistant to fully (6) or partially (17) susceptible to PR6 . All fully susceptible mutants carried rearrangements at the Xa21 locus as detected by PCR and Southern hybridization . For the partially susceptible mutants, no changes were detected at the Xa21 locus based on Southern and PCR analyses . However, two of these mutants were confirmed via genetic analysis to have mutations at the Xa21 locus . Partially susceptible mutants exhibited variation in level of susceptibility to different Xoo strains, suggesting that they may carry different mutations required for the Xa21-mediated resistance . The mutants identified in this study provide useful materials for dissecting the Xa21-mediated resistance pathway in rice.

Planta, 2003 Jul, 217(3), 356 - 66 Epub 2003 Mar 11.
The unusual Arabidopsis extensin gene atExt1 is expressed throughout plant development and is induced by a variety of biotic and abiotic stresses; Merkouropoulos G et al.; We detail the expression of the Arabidopsis thaliana (L.) Heynh . atExt1 extensin gene . atExt1 is normally expressed in roots and inflorescences, and is induced by wounding, exogenously supplied salicylic acid, methyl jasmonate, auxins and brassinosteroids . Northern assays and histochemical analysis of transgenics expressing an atExt1:: gus fusion show that this gene is also induced by the brassica pathogen Xanthomonas campestris pv . campestris and that this induction is restricted to tissues close to the site of infection . Expression at regions of abscission and senescence also implicates atExt1 in these important developmental processes.

FEMS Microbiol Lett, 2003 Sep 12, 226(1), 145 - 50
High-quality mutant libraries of Xanthomonas oryzae pv . oryzae and X . campestris pv . campestris generated by an efficient transposon mutagenesis system; Sun Q et al.; A novel transposon mutagenesis system for the phytopathogenic bacteria Xanthomonas oryzae pv . oryzae (Xoo) and X . campestris pv . campestris (Xcc) was developed using a Tn5-based transposome . A highly efficient transformation up to 10(6) transformants per microg transposon DNA was obtained . Southern blot and thermal asymmetric interlaced polymerase chain reaction analyses of Tn5 insertion sites suggested a random mode of transposition . The transposition was stable in the transformants for 20 subcultures . Eighteen thousand and 17000 transformants for Xoo and Xcc, respectively, were generated, corresponding to 4X ORF coverage of the genomes . The libraries will facilitate the identification of pathogenicity-related genes as well as functional genomic analysis in Xoo and Xcc.

Plant Physiol, 2003 Sep, 133(1), 339 - 47
A developmental response to pathogen infection in Arabidopsis; Korves TM et al.; We present evidence that susceptible Arabidopsis plants accelerate their reproductive development and alter their shoot architecture in response to three different pathogen species . We infected 2-week-old Arabidopsis seedlings with two bacterial pathogens, Pseudomonas syringae and Xanthomonas campestris, and an oomycete, Peronospora parasitica . Infection with each of the three pathogens reduced time to flowering and the number of aerial branches on the primary inflorescence . In the absence of competition, P . syringae and P . parasitica infection also increased basal branch development . Flowering time and branch responses were affected by the amount of pathogen present . Large amounts of pathogen caused the most dramatic changes in the number of branches on the primary inflorescence, but small amounts of P . syringae caused the fastest flowering and the production of the most basal branches . RPS2 resistance prevented large changes in development when it prevented visible disease symptoms but not at high pathogen doses and when substantial visible hypersensitive response occurred . These experiments indicate that phylogenetically disparate pathogens cause similar changes in the development of susceptible Arabidopsis . We propose that these changes in flowering time and branch architecture constitute a general developmental response to pathogen infection that may affect tolerance of and/or resistance to disease.

J Appl Microbiol, 2003, 95(4), 656 - 63
Evidence for dose-dependent effects on plant growth by Stenotrophomonas strains from different origins; Suckstorff I et al.; AIMS: To assess the influence of Stenotrophomonas on plants, the interaction of 16 Stenotrophomonas strains from clinical and environmental sources with strawberry plant seedlings was analysed . METHODS AND RESULTS: In vitro, all Stenotrophomonas strains influenced plant growth when applied to seedlings . Whereas most of the Stenotrophomonas strains promoted root growth and hair development, a statistically significantly negative influence on the length of stem was found . Although strains from a clinical origin also showed statistically significant effects on plants, this was generally lower when compared with environmental strains . For three selected strains, a strong dose-dependent effect was observed for all parameters . In vitro, a correlation was found between plant growth promotion and production of a plant growth hormone, indole-3-acetic acid (IAA) . Xanthomonas campestris, a phylogenetically very closely related species to Stenotrophomonas, was used as a phytopathogenic control . It too confirmed the reduction of plant growth in this in vitro system . CONCLUSIONS: Independent of their origin, Stenotrophomonas strains can produce IAA in vitro and subsequently, influence plant growth . The effect of Stenotrophomonas presence on plants was dose-dependent . SIGNIFICANCE AND IMPACT OF THE STUDY: The dose-dependent effect of Stenotrophomonas, a bacterium of both biotechnological and medical interest, is of great interest for biocontrol applications of plant-associated strains . This paper is the first report that clearly demonstrates the phytopathogenic capacity of Stenotrophomonas.

Exp Biol Med (Maywood), 2003 Sep, 228(8), 926 - 34
Partial characterization of chorionic gonadotropin-like binding sites from the bacteria Xanthomonas maltophilia; Edwards JG et al.; The gram-negative bacterium, Xanthomonas maltophilia, has low- and high-affinity luteinizing hormone/chorionic gonadotropin (LH/CG)-binding sites, similar to the LH/CG receptor found in mammals . Although the low-affinity site binds both LH and human CG (hCG), the high-affinity site is specific for hCG . In the current investigation, these two binding sites were independently isolated from X . maltophilia for further characterization . To isolate functional binding sites, we developed a solubilization method using the detergent zwittergent 3,14 and high glycerol concentrations that allowed for the maintenance of ligand-binding integrity . Gel filtration experiments established molecular weights of 170 and 11.5 kDa for the two binding sites, which were supported by data from photoaffinity labeling and ultracentrifugation experiments . Gel filtration data also suggested the presence of a third binding site of 5.4 kDa . The 170-kDa site had a binding affinity of Kd = 12 x 10(-6) and bound both LH and hCG . The small molecular weight site had an affinity of Kd = 9.4 x 10(-8) and was CG specific . Collectively, these data demonstrate the presence of multiple hormone binding sites in X . maltophilia that differ in molecular size, binding affinity, and ligand specificity.

Phytochemistry, 2003 Sep, 64(1), 219 - 25
8-Hydroxy-(+)-delta-cadinene is a precursor to hemigossypol in Gossypium hirsutum; Wang YH et al.; {(3)H}(+)-delta-Cadinene and its 8-hydroxy derivative, prepared from (1RS)-{1-(3)H}FPP by the action of one and two recombinant enzymes, respectively, were infiltrated into cotyledons of bacterial blight-resistant cotton plants as they biosynthesized sesquiterpene phytoalexins in response to infection by Xanthomonas campestris pv . malvacearum . Following both treatments, tritium appeared in the HPLC fraction that contained hemigossypol . Hemigossypol was isolated from the cotyledons that had been treated with {(3)H}(+)-8-hydroxy-delta-cadinene and was trimethylsilylated and purified . In two experiments, specific radioactivity of the hemigossypol derivative indicated that 5% and 10%, respectively, of the {(3)H}(+)-8-hydroxy-delta-cadinene had been converted to hemigossypol.

Plant J, 2003 Jan, 33(1), 131 - 7
Direct delivery of bacterial avirulence proteins into resistant Arabidopsis protoplasts leads to hypersensitive cell death; Wu Y et al.; Many bacterial avirulence (Avr) proteins, including the Pseudomonas syringae proteins, AvrRpt2 and AvrB, appear to be recognized inside the host plant cell by resistance mechanisms mediated by the cognate resistance (R) genes . It is thought that Avr proteins are either delivered directly into the host cell via the bacterial type III secretion system (TTSS) or taken up by the plant cell following secretion into the apoplast through the TTSS . Recently, it was shown that the Xanthomonas campestris AvrBs2 protein can be delivered directly into the host plant cell by the TTSS . However, it is not known whether other type III effectors of phytopathogens behave similarly . Here, using a novel protein transfection method, we demonstrate that AvrRpt2 and AvrB must enter the plant cell to be recognized by R gene-mediated mechanisms . First, we established a hypersensitive cell death assay for protoplasts using the membrane-impermeable, nuclear-staining dye, YO-PRO-1, and transgenic Arabidopsis plants that carry an inducible avrRpt2 gene . Second, we transfected E . coli-produced AvrRpt2 or AvrB proteins into Arabidopsis protoplasts using a protein transfection kit based on the carrier peptide Pep-1, and demonstrated that hypersensitive cell death occurs in a gene-for-gene-specific manner . In contrast, these Avr proteins failed to elicit hypersensitive cell death when they were applied to protoplasts without the carrier peptide . We conclude that our preparations of E . coli-produced AvrRpt2 and AvrB are active, that AvrRpt2 and AvrB must be delivered into the plant cell to be recognized, and that a method based on a carrier peptide can be used to introduce proteins into plant cells.

Biochem Biophys Res Commun, 2003 Aug 1, 307(3), 647 - 52
Flagellin gene fliC of Xanthomonas campestris is upregulated by transcription factor Clp; Lee MC et al.; Clp, a homologue of cyclic AMP receptor protein (CRP), of Xanthomonas campestris regulates the expression of many genes . In this study, proteomic analysis showed the amounts of several extracellular proteins in a clp mutant to be reduced, including the flagellin encoded by fliC . Transcriptional fusion assay showed that activity of fliC promoter is reduced by 2.3-fold in clp mutant compared to the wild-type, coincident with the protein levels . The clp mutant is slightly reduced in motility; however, electron microscopy showed no significant change in the monotrichous flagellation . A fleQ homologue with conserved Clp-binding site in the upstream region is present in the fully sequenced X . campestris genome, suggesting that regulation of the flagellar genes is similar to that of Pseudomonas aeruginosa in involving Vfr, the CRP homologue, and FleQ in a cascade manner except that Vfr downregulates fleQ . Concomitant loss of flagellum and motility in fliC mutant and absence of a second homologue in the genome sequence suggest that X . campestris possesses a single flagellin gene, fliC . In addition, mutation of this gene does not affect virulence.

Biotechnol Prog, 2003 Jul-Aug, 19(4), 1190 - 8
Productivity improvement in xanthan gum fermentation using multiple substrate optimization; Chaitali M et al.; A novel and more comprehensive formulation of the optimal control problem that reflects the operational requirements of a typical industrial fermentation has been proposed in this work . This formulation has been applied to a fed-batch bioreactor with three control variables, i.e., feed rates of carbon source, nitrogen source, and an oxygen source, to result in a 148.7% increase in product formation . Xanthan gum production using Xanthomonas campestris has been used as the model system for this optimization study, and the liquid-phase oxygen supply strategy has been used to supply oxygen to the fermentation . The formulated optimization problem has several constraints associated with it due to the nature of the system . A robust stochastic technique, differential evolution, has been used to solve this challenging optimization problem . The infinite dimensional optimization problem has been approximated to a finite dimensional one by control vector parametrization . The state constraints that are path constraints have been addressed by using penalty functions and by integrating them over the total duration to ensure a feasible solution . End point constraints on final working volume of the reactor and on the final residual concentrations of carbon and nitrogen sources have been included in the problem formulation . Further, the toxicity of the oxygen source, H(2)O(2), has been addressed by imposing a constraint on its maximum usable concentration . In addition, the initial volume of the bioreactor contents and feed concentrations have been handled as decision variables, which has enabled a well-grounded choice for their values from the optimization procedure; adhoc values are normally used in the industry . All results obtained by simulation have been validated experimentally with good agreements between experimental and simulated values.

J Mol Biol, 2003 Jul 18, 330(4), 735 - 48
Genome of Xanthomonas oryzae bacteriophage Xp10: an odd T-odd phage; Yuzenkova J et al.; Xp10 is a lytic bacteriophage of the phytopathogenic bacterium Xanthomonas oryzae . Though morphologically Xp10 belongs to the Syphoviridae family, it encodes its own single-subunit RNA polymerase characteristic of T7-like phages of the Podoviridae family . Here, we report the determination and analysis of the 44,373 bp sequence of the Xp10 genome . The genome is a linear, double-stranded DNA molecule with 3' cohesive overhangs and no terminal repeats or redundancies . Half of the Xp10 genome contains genes coding for structural proteins and host lysis functions in an arrangement typical for temperate dairy phages that are related to the Escherichia coli lambda phage . The other half of the Xp10 genome contains genes coding for factors of host gene expression shut-off, enzymes of viral genome replication and expression . The two groups of genes are transcribed divergently and separated by a regulatory region, which contains divergent promoters recognized by the host RNA polymerase . Xp10 has apparently arisen through a recombination between genomes of widely different phages . Further evidence of extensive gene flux in the evolution of Xp10 includes a high fraction (10%) of genes derived from an HNH-family endonuclease, and a DNA-dependent DNA polymerase that is closer to a homolog from Leishmania than to DNA polymerases from other phages or bacteria.

Plant Cell Environ, 2003 Jun, 26(6), 915 - 928
Three pathogen-inducible genes encoding lipid transfer protein from pepper are differentially activated by pathogens, abiotic, and environmental stresses; Jung HW et al.; The three cDNA clones, CALTPI, CALTPII, and CALTPIII, corresponding to pepper lipid transfer protein (LTP) genes were isolated from a pepper (Capsicum annuum) cDNA library from hypersensitive response (HR) lesions of leaves infected with Xanthomonas campestris pv . vesicatoria . The CALTP genes are well conserved in their coding region with 57-72% identity at the amino acid level, but display 72-83% identity at the nucleotide sequence level . The transcripts of the three CALTP genes differentially accumulated in pepper leaf, stem, and fruit tissues infected by X . campestris pv . vesicatoria, Phytophthora capsici and Colletotrichum gloeosporioides . The CALTP genes were also strongly induced in the systemic, upper leaves after immunization on lower leaves by either pathogenic or non-pathogenic bacteria . In situ hybridization results showed that the CALTPI mRNA was localized in phloem cells of vascular tissues in pepper leaf, stem and fruit tissues after pathogen infection . CALTPI and CALTPIII genes were predominantly expressed in various pepper tissues infected by pathogens, while infection by P . capsici and C . gloeosporioides did not induce the transcription of the CALTPII gene . Ethylene, methyl jasmonate and abscisic acid induced CALTPI and III gene expression in pepper leaves . Drought, high salinity, low temperature and wounding stresses also induced the expression of the CALTPI and CALTPIII genes in a similar manner . In contrast, only high salinity induced the CALTPII expression that was not generally affected by abiotic and other environmental stimuli . When compared with each other and with LTPs from other plants, CALTPI is more distantly related than CALTPII and CALTPIII sequences, indicating that the three pepper CALTP genes represent two different classes . These results thus show that CALTPI and CALTPIII genes, although different in sequence structure, are transcriptionally activated in pepper tissues by pathogen infection as well as abiotic and environmental stresses.

Biotechnol Prog, 2003 May-Jun, 19(3), 822 - 7
Development of a phenomenological modeling approach for prediction of growth and xanthan gum production using Xanthomonas campestris; Letisse F et al.; An unstructured kinetic model for xanthan production is described and fitted to experimental data obtained in a stirred batch reactor . The culture medium was composed of several nitrogen sources (soybean hydrolysates, ammonium and nitrate salts) consumed sequentially . The model proposed is able to describe this sequential consumption of nitrogen sources, the consumption of inorganic phosphate and carbon, the evolution of biomass, and production of xanthan . The parameter estimation has been performed by fitting the kinetic model in differential form to experimental data . Runs of the model for simulating xanthan gum production as a function of the initial concentration of inorganic phosphate have shown the positive effect of phosphate limitation on xanthan yield, though diminishing rates of production . The model was used to predict the kinetic parameters for a medium containing a 2-fold lower initial phosphate concentration . When tested experimentally, the measured fermentation parameters were in close agreement with the predicted model values, demonstrating the validity of the model.

Appl Environ Microbiol, 2003 Jun, 69(6), 3484 - 91
Nutritional similarity between leaf-associated nonpathogenic bacteria and the pathogen is not predictive of efficacy in biological control of bacterial spot of tomato; Dianese AC et al.; It has been demonstrated that for a nonpathogenic, leaf-associated bacterium, effectiveness in the control of bacterial speck of tomato is correlated with the similarity in the nutritional needs of the nonpathogenic bacterium and the pathogen Pseudomonas syringae pv . tomato . This relationship was investigated further in this study by using the pathogen Xanthomonas campestris pv . vesicatoria, the causal agent of bacterial spot of tomato, and a collection of nonpathogenic bacteria isolated from tomato foliage . The effects of inoculation of tomato plants with one of 34 nonpathogenic bacteria prior to inoculation with the pathogen X . campestris pv . vesicatoria were quantified by determining (i) the reduction in disease severity (number of lesions per square centimeter) in greenhouse assays and (ii) the reduction in leaf surface pathogen population size (log(10) of the number of CFU per leaflet) in growth chamber assays . Nutritional similarity between the nonpathogenic bacteria and X . campestris pv . vesicatoria was quantified by using either niche overlap indices (NOI) or relatedness in cluster analyses based upon in vitro utilization of carbon or nitrogen sources reported to be present in tomato tissues or in Biolog GN plates . In contrast to studies with P . syringae pv . tomato, nutritional similarity between the nonpathogenic bacteria and the pathogen X . campestris pv . vesicatoria was not correlated with reductions in disease severity . Nutritional similarity was also not correlated with reductions in pathogen population size . Further, the percentage of reduction in leaf surface pathogen population size was not correlated with the percentage of reduction in disease severity, suggesting that the epiphytic population size of X . campestris pv . vesicatoria is not related to disease severity and that X . campestris pv . vesicatoria exhibits behavior in the phyllosphere prior to lesion formation that is different from that of P . syringae pv . tomato.

Fitoterapia, 2003 Jun, 74(4), 394 - 6
Antibacterial activity of Rosa damascena essential oil; Basim E et al.; The essential oil of Rosa damascena petals was evaluated for its antibacterial effects against three strains of Xanthomonas axonopodis spp . vesicatoria . The essential oil may be a potential control agent in the management of the disease caused by X.a . vesicatoria in tomato and pepper plants.

Biochemistry (Mosc), 2003 Apr, 68(4), 458 - 63
Intracellular peptidoglycan hydrolases of the bacterium Xanthomonas campestris XL-1; Sitkin BV et al.; A system of intracellular peptidoglycan hydrolases of Xanthomonas campestris XL-1 comprises about 10 enzymes of different localization and substrate specificity . Seven enzymes (A(1)-A(7)) are localized in cytosol, one enzyme (A(8)) in periplasm, and two enzymes (A(9), A(10)) were found in the fraction of cell walls and membranes . While the culture is entering the logarithmic growth stage from the stationary stage, a change occurs in the activity of the cytosolic enzymes: A(1) significantly increases, and A(5) and A(6) decrease . The spectrum of cytosolic enzymes also depends on the growth medium composition . The enzyme A(7) present in cells secreting extracellular enzymes (medium 5/5) was not found in non-secreting cells (LB medium) . Unlike extracellular enzymes, intracellular peptidoglycan hydrolases are primarily acidic proteins . The data indicate that the system of intracellular peptidoglycan hydrolases of X . campestris is under complex and strict regulation.

Appl Microbiol Biotechnol, 2003 Jun, 61(5-6), 479 - 87 Epub 2003 Apr 01.
Esterase EstE from Xanthomonas vesicatoria ( Xv_EstE) is an outer membrane protein capable of hydrolyzing long-chain polar esters; Talker-Huiber D et al.; A new esterase gene from Xanthomonas vesicatoria (formerly X . campestris) DSM 50861 was identified, cloned from a chromosomal gene library and overexpressed in Escherichia coli . The corresponding DNA fragment contains an ORF of 1,818 bp, encoding a hydrolase of the GDSL esterase family . A protein of about 67 kDa, named Xv_EstE, was expressed from this fragment . A N-terminal signal peptide was processed under low-expression conditions, yielding a 63-kDa mature protein . The predicted amino acid sequence showed distinct homology to esterases of the GDSL family . Based on homology, a catalytic triad Gly-Asp-Ser could be defined . Amino acid sequence alignments and computer-assisted structure prediction indicated the presence of a carboxyl-terminal beta-barrel membrane domain which might facilitate binding of Xv_EstE to the outer membrane . This could be verified by differential cell fractionation experiments, in which Xv_EstE was exclusively found in the outer membrane fraction . Xv_EstE showed preferential hydrolytic activity on short chain (up to C(8)) and para-substituted nitrophenylesters as substrates . However, only long-chain 1-hydroxy-pyrene-3,6,8-trisulfonic acid (HPTS)-fatty acid esters were hydrolyzed . Xv_EstE was also found to be active on a series of substrates of industrial interest, such as 1-methylprop-2-ynyl acetate, for which an enantioselectivity up to 93% ee could be recognized.

Theor Appl Genet, 2003 May, 106(8), 1467 - 72 Epub 2003 Feb 12.
Genetic and physical mapping of a new gene for bacterial blight resistance in rice; Yang Z et al.; The inheritance of resistance for bacterial blight, caused by Xanthomonas oryzae pv . oryzae ( Xoo), was studied in Minghui 63, an elite restorer line for a number of widely used rice hybrids in China . A new dominant gene against a Chinese Xoo strain JL691 in both the seedling and adult stages was identified in Minghui 63 and designated as Xa26( t) . Using a total of 477 highly susceptible individuals from an F(2) population, the Xa26( t) locus was mapped to a region of about 1.68 cM . This locus co-segregated with marker R1506 and was 0.21 cM from marker RM224 on one side and 1.47 cM from marker Y6855RA on the other side, in rice chromosome 11 . A contig map, composed of five non-redundant bacterial artificial chromosome (BAC) clones and spanning approximately 500 kb in length, was constructed . Analysis of recombination events in the Xa26( t) region with the highly susceptible F(2) individuals anchored the gene locus to a region covered by three overlapped BAC clones . Assay of the lines showing a double crossover in marker loci flanking Xa26( t), in a population of recombinant inbred lines carrying Xa26( t), further delineated the gene to a 20-kb fragment . The Xa26( t) locus is tightly linked to another bacterial blight resistance gene locus, Xa4.

Curr Microbiol, 2003 Apr, 46(4), 251 - 5
Compositional difference of the exopolysaccharides produced by the virulent and virulence-deficient strains of Xanthomonas oryzae pv . oryzae; Kumar A et al.; Xanthomonas oryzae pv . oryzae, the bacterial blight pathogen of rice, is known to produce phytotoxic polysaccharides . The extracellular polysaccharide (EPS) was isolated from virulent (BXO1) and virulence-deficient gum G mutant (BXO1002) strains of X . oryzae pv . oryzae and characterized using fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) . Data from the FT-IR suggested that the aldehyde (R-CHO) group and C=O of acid anhydride are present in BXO1 but absent in BXO1002 . The (1)H-NMR spectra showed the presence of an acetyl amine of hexose or pentose, free amines of glucose, an beta-anomeric carbon of hexose and pentose, hydrogen next to hydroxyl group, an acetyl amine of hexose and pentose in the polysaccharides of both BXO1 and BXO1002, and the absence of alpha-anomeric carbon of hexose or pentose and the glucuronic acid in the polysaccharides produced by BXO1002 . The test for glucuronic acid also confirmed the absence of glucuronic acid in the polysaccharides of BXO1002 and the presence glucuronic acid (32 microg/mg) in the polysaccharides produced by BXO1.

J Bacteriol, 2003 May, 185(10), 3155 - 66
Characterization of the Xanthomonas axonopodis pv . glycines Hrp pathogenicity island; Kim JG et al.; We sequenced an approximately 29-kb region from Xanthomonas axonopodis pv . glycines that contained the Hrp type III secretion system, and we characterized the genes in this region by Tn3-gus mutagenesis and gene expression analyses . From the region, hrp (hypersensitive response and pathogenicity) and hrc (hrp and conserved) genes, which encode type III secretion systems, and hpa (hrp-associated) genes were identified . The characteristics of the region, such as the presence of many virulence genes, low G+C content, and bordering tRNA genes, satisfied the criteria for a pathogenicity island (PAI) in a bacterium . The PAI was composed of nine hrp, nine hrc, and eight hpa genes with seven plant-inducible promoter boxes . The hrp and hrc mutants failed to elicit hypersensitive responses in pepper plants but induced hypersensitive responses in all tomato plants tested . The Hrp PAI of X . axonopodis pv . glycines resembled the Hrp PAIs of other Xanthomonas species, and the Hrp PAI core region was highly conserved . However, in contrast to the PAI of Pseudomonas syringae, the regions upstream and downstream from the Hrp PAI core region showed variability in the xanthomonads . In addition, we demonstrate that HpaG, which is located in the Hrp PAI region of X . axonopodis pv . glycines, is a response elicitor . Purified HpaG elicited hypersensitive responses at a concentration of 1.0 micro M in pepper, tobacco, and Arabidopsis thaliana ecotype Cvi-0 by acting as a type III secreted effector protein . However, HpaG failed to elicit hypersensitive responses in tomato, Chinese cabbage, and A . thaliana ecotypes Col-0 and Ler . This is the first report to show that the harpin-like effector protein of Xanthomonas species exhibits elicitor activity.

Carbohydr Res, 2003 May 1, 338(10), 1023 - 31
Efficient synthesis of a heptasaccharide, the repeating unit of the O-chain lipopolysaccharide produced by Xanthomonas campestris strain 642; Zhang J et al.; alpha-L-Rhap-(1-->3)-alpha-L-Rhap-(1-->2)-alpha-L-Rhap-(1-->3)-{beta-D-Xylp-(1-->2)-}{beta-D-Xylp-(1-->4)-}alpha-L-Rhap-(1-->3)-alpha-L-Rhap, the repeating unit of the O-chain lipopolysaccharide produced by Xanthomonas campestris strain 642 was synthesized as its methyl glycoside via 3-O-selective glycosylation of methyl alpha-L-rhamnopyranosyl-(1-->3)-2,4-di-O-benzoyl-alpha-L-rhamnopyranoside (9) with 2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl-(1-->3)-2,4-di-O-benzoyl-alpha-L-rhamnopyranosyl-(1-->2)-3,4-di-O-benzoyl-alpha-L-rhamnopyranosyl trichloroacetimidate (8), followed by dixylosylation with 2,3,4-tri-O-benzoyl-alpha,beta-D-xylopyranosyl trichloroacetimidate (12) and subsequent deacylation.

Infez Med, 2002 Jun, 10(2), 107 - 14
{Effects induced by the introduction of highly active antiretroviral therapy (HAART) on disseminated bacterial infection during HIV disease}; Manfredi R et al.; In order to assess the frequency, risk factors, etiology, and clinical outcome of HIV-related sepsis and bacteremia, according to the introduction of highly active antiretroviral therapy (HAART), all episodes occurred in patients hospitalized during years 1993-1995 (pre-HAART era), have been compared with those diagnosed after HAART introduction (years 1997-2000) . On the whole, 498 patients suffered from sepsis/bacteremia in the two considered time periods, but the frequency of this complication proved significantly lower during the last 4 years, as opposed to the pre-HAART period (5.3 versus 18.2 episodes per patient-year: p<.0001) . Among potential risk factors, during the last 4 years a significant rise of mean CD4+ lymphocyte count was observed (p<.0001), together with a reduced frequency of neutropenia (absolute neutrophil count <1000 cells/ L) (p<.02), and a less frequent association with an advanced HIV disease (stage C, CDC) (p<.03) . Despite a remarkably reduced mean duration of admission, during the HAART era a significant increase of nosocomial- versus community-acquired infection occurred (p<.002), with a related greater frequency of gram-negative bacilli of environmental origin: Pseudomonas, Xanthomonas (Stenotrophomonas), Acinetonbacter spp., and non-fermenting bacilli (p<.05) . No significant difference was noticed between the two considered periods, as to patients' age, gender, and type of exposure to HIV, use of central vascular lines, prior administration of steroids, antimicrobials, and cotrimoxazole, as well as disease outcome (including the frequency of related deaths) . On the whole, the significant drop of frequency of HIV-associated sepsis/bacteremia occurred after the introduction of HAART (over 3.4-fold, compared with that observed prior to HAART use), proved associated with a reduced degree of immunodeficiency, and a less advanced underlying disease . The proportional increase of nosocomial infections and related pathogens did not match with the apparently significant reduction of mean admission time . A careful and continued monitoring of epidemiological, microbiological, clinical, and treatment features of disseminated bacterial disease looks mandatory even during the HAART era, in order to update therapeutic and prophylactic strategies of HIV disease management.

Mol Genet Genomics, 2003 Jun, 269(3), 331 - 9 Epub 2003 Mar 27.
Three types of defense-responsive genes are involved in resistance to bacterial blight and fungal blast diseases in rice; Wen N et al.; Bacterial blight and fungal blast diseases of rice, caused by Xanthomonas oryzae pv . oryzae and Pyricularia grisea Sacc., respectively, are two of the most devastating diseases in rice worldwide . To study the defense responses to infection with each of these pathogens, expression profiling of 12 defense-responsive genes was performed using near-isogenic rice lines that are resistant or susceptible to bacterial blight and fungal blast, respectively, and rice cultivars that are resistant or susceptible to both pathogens . All 12 genes showed constitutive expression, but expression levels increased in response to infection . Based on their expression patterns in 12 host-pathogen combinations, these genes could be classified into three types, pathogen non-specific (6), pathogen specific but race non-specific (4) and race specific (2) . Most of the 12 genes were only responsive during incompatible interactions . These results suggest that bacterial blight and fungal blast resistances share common pathway(s), but are also regulated by different defense pathways in rice . Activation of the corresponding R gene is the key step that initiates the action of these genes in defense responses . The chromosomal locations and pathogen specificities of seven of the 12 genes were consistent with those of previously identified quantitative trait loci for rice disease resistance, which indicates that some of the 12 genes studied may have a phenotypic impact on disease resistance in rice.

Theor Appl Genet, 2003 Jun, 107(1), 62 - 73 Epub 2003 Apr 03.
High resolution genetic mapping and candidate gene identification at the xa5 locus for bacterial blight resistance in rice ( Oryza sativa L.); Blair MW et al.; The xa5 resistance gene from rice provides recessive, race-specific resistance to bacterial blight of rice caused by the pathogen Xanthomonas oryzae pv oryzae . A high-resolution genetic map of the chromosomal region surrounding xa5 was developed by placing 44 DNA markers on the distal end of rice chromosome 5 . The basis for mapping was a PCR-based screening of 1,016 F(2) individuals derived from a cross between a near-isogenic line (NIL) and its corresponding recurrent parent to identify recombinants in the region . Recombinant F(2) individuals were progeny tested using F(3) families inoculated with the Philippine strain PXO 61 of bacterial blight pathogen . The xa5 gene was mapped to a 0.5-cM interval between the markers RS7 and RM611, which spanned an interval of approximately 70 kb and contained a total of 11 open reading frames . Sequence data for the locus was generated from an Indica (the IR24 isoline, IRBB21) BAC covering part of the region and compared to other overlapping Indica (cv 93-11) and Japonica (cv Nipponbare) sequences . Candidate-gene analysis revealed that a basal transcription factor (TFIIa), an ABC transporter, a tRNA synthase, a MAP kinase and a cysteine protease, as well as four unknown, hypothetical or putative proteins, are encoded at the locus and could be potential candidates for the resistance gene product . The mechanism by which these genes could provide recessive, race-specific resistance will be elucidated by map-based cloning of the xa5 gene.

J Vet Med B Infect Dis Vet Public Health, 2003 Mar, 50(2), 102 - 4
An outbreak of lymphadenitis associated with Stenotrophomonas (Xanthomonas) maltophilia in Omani goats; Johnson EH et al.; Stenotrophomonas maltophilia is a commonly isolated organism from human clinical specimens and is gaining significance as a pathogen in immunocompromised patients and nosocomial infections . In most cases it is difficult to establish the source of human infections . In veterinary medicine, S . maltophilia is not generally considered a primary pathogen . In the present study, we report the occurrence of 16 cases of caprine abscess from which S . maltophilia was isolated in pure culture from 15 animals . In six animals, the abscesses were confined to the pre-scapular lymph nodes but in the remaining nine, the cutaneous abscesses were multiple and extended from the neck to the inguinal area . The possibility is suggested that goats in Oman, which often live in close proximity to humans, might potentially serve as a reservoir of infection.

Surg Today, 2003, 33(3), 224 - 8
Liver abscess caused by Stenotrophomonas maltophilia: report of a case; Petri A et al.; We report the case of a melioidosis-like abscess of the liver caused by Stenotrophomonas (Xanthomonas) maltophilia infection in a Chinese man living in Hungary . Although this appears to be the first documentation of a liver abscess of this origin in a nonimmunocompromised patient, our case report demonstrates that this common facultative pathogen can also cause liver abscess and sepsis . After repeated negative blood cultures, histological examinations of liver biopsies suggested the possibility of chronic melioidosis, but the microbiological examination performed directly on the same specimen identified a Stenotrophomonas maltophilia infection . Surgical drainage was performed and sulphamethoxazole/trimethoprim therapy was commenced, after which the patient recovered fully . The facultative pathogen S . maltophilia, which most often causes nosocomial infections, may cause severe sepsis and liver abscess . We wish to draw attention to the fact that the antibiotic sensitivity of S . maltophilia is not necessarily the same in vivo and in vitro . This can create difficulties in both diagnosis and treatment.

Mol Plant Microbe Interact, 2003 Mar, 16(3), 196 - 205
Expression of peroxidase-like genes, H2O2 production, and peroxidase activity during the hypersensitive response to Xanthomonas campestris pv . vesicatoria in Capsicum annuum; Do HM et al.; Pepper ascorbate peroxidase-like (CAPOA1), thioredoxin peroxidase-like (CAPOT1), and peroxidase-like (CAPO1) clones were isolated from pepper leaves inoculated with avirulent strain Bv5-4a of Xanthomonas campestris pv . vesicatoria . CAPOA1, CAPOT1, and CAPO1 mRNA disappeared 18 to 30 h after the bacterial infection when the hypersensitive response (HR) was visible . In contrast, peroxidase activity reached a peak at 18 h after infection and then declined at 24 and 30 h when H2O2 accumulation level was maximal . These results suggest that the striking accumulation of H2O2 and strong decrease in peroxidase activity during the programmed cell death may be due to the strong suppression of CAPOA1, CAPOT1, and CAPO1 gene expression . Infection by Phytophthora capsici or Colletotricum gloeosporioides also induced the expression of the three putative peroxidase genes in pepper tissues . CAPOA1 mRNAs were in situ localized in phloem areas of vascular bundles in pepper tissues infected by Colletotricum . coccodes, P . capsici, or C . gloeosporioides . Exogenous treatment with H2O2 strongly induced the CAPOA1 and CAPOT1 transcription 1 h after treatment, while the CAPO1 transcripts accumulated 12 h after H2O2 treatment . We suggest that pepper ascorbate peroxidase and thioredoxin peroxidase genes may function as regulators of H2O2 level and total peroxidase activity in the oxidative burst during the HR to incompatible pathogen interaction in pepper plant.

Biochem Biophys Res Commun, 2003 Mar 21, 302(4), 878 - 84
Involvement of tonB-exbBD1D2 operon in infection of Xanthomonas campestris phage phi L7; Hung CH et al.; phi L7 is a lytic bacteriophage infecting Xanthomonas campestris pv . campestris, a Gram-negative bacterium producing xanthan gum and causing black rot in crucifers . A mutant resistant to phi L7 was isolated by Tn5 mutagenesis . Sequence analysis indicated that the gene responsible for the mutation is tonB encoding an inner membrane protein previously shown to be required for iron uptake and pathogenesis . This gene is clustered with three other genes, tonB-exbB-exbD1-exbD2 . Results of insertional mutations, DNA and protein sequence analyses, phage sensitivity tests, transfection tests, complementation tests, and phage adsorption assays together with the cellular location of the proteins indicate that TonB, ExbB, and ExbD1 are essential for penetration of phage phi L7 . The genome organization, structural features of the tonB-exb region, and transcriptional analyses including Northern hybridization, reporter assays, and primer extension together indicate that the four genes are organized into an operon.

Phytochemistry, 2003 Mar, 62(5), 723 - 32
Xanosporic acid, an intermediate in bacterial degradation of the fungal phototoxin cercosporin; Mitchell TK et al.; The red fungal perylenequinone phototoxin cercosporin is oxidized by Xanthomonas campestris pv zinniae to a non-toxic, unstable green metabolite xanosporic acid, identified via its lactone as 1,12-bis(2'R-hydroxypropyl)-4,9-dihydroxy-6,7-methylenedioxy-11-methoxy-3-oxaperylen-10H-10-one-2-carboxylic acid . Xanosporolactone was isolated in approximately 2:1 ratio of M:P atropisomers.

Plant J, 2003 Mar, 33(5), 887 - 98
Brassinosteroid functions in a broad range of disease resistance in tobacco and rice; Nakashita H et al.; Brassinolide (BL), considered to be the most important brassinosteroid (BR) and playing pivotal roles in the hormonal regulation of plant growth and development, was found to induce disease resistance in plants . To study the potentialities of BL activity on stress responding systems, we analyzed its ability to induce disease resistance in tobacco and rice plants . Wild-type tobacco treated with BL exhibited enhanced resistance to the viral pathogen tobacco mosaic virus (TMV), the bacterial pathogen Pseudomonas syringae pv . tabaci (Pst), and the fungal pathogen Oidium sp . The measurement of salicylic acid (SA) in wild-type plants treated with BL and the pathogen infection assays using NahG transgenic plants indicate that BL-induced resistance does not require SA biosynthesis . BL treatment did not induce either acidic or basic pathogenesis-related (PR) gene expression, suggesting that BL-induced resistance is distinct from systemic acquired resistance (SAR) and wound-inducible disease resistance . Analysis using brassinazole 2001, a specific inhibitor for BR biosynthesis, and the measurement of BRs in TMV-infected tobacco leaves indicate that steroid hormone-mediated disease resistance (BDR) plays part in defense response in tobacco . Simultaneous activation of SAR and BDR by SAR inducers and BL, respectively, exhibited additive protective effects against TMV and Pst, indicating that there is no cross-talk between SAR- and BDR-signaling pathway downstream of BL . In addition to the enhanced resistance to a broad range of diseases in tobacco, BL induced resistance in rice to rice blast and bacterial blight diseases caused by Magnaporthe grisea and Xanthomonas oryzae pv . oryzae, respectively . Our data suggest that BDR functions in the innate immunity system of higher plants including dicotyledonous and monocotyledonous species.

Theor Appl Genet, 2003 Feb, 106(4), 683 - 7 Epub 2002 Oct 29.
Identification of a 47-kb DNA fragment containing Xa4, a locus for bacterial blight resistance in rice; Sun X et al.; Bacterial blight caused by Xanthomonas oryzae pv oryzae is a devastating disease in rice worldwide . The resistance gene Xa4 has been widely used in breeding programs and played an important role in protecting rice from this disease . Using 642 highly susceptible individuals and a random sample of 255 individuals from an F(2) population developed from a cross between IRBB4 and IR24, the Xa4 gene was genetically mapped to a region less than 1 cM . A contig map was constructed for the Xa4 region consisting of six non-redundant bacterial artificial chromosome (BAC) clones and spanning approximately 500 kb in length . Analysis of recombination events in the Xa4 region located the gene locus to one BAC, 3H8 . Assay of the recombinants using the subclones of 3H8 in combination with sequence analysis further narrowed the Xa4 locus down to a 47-kb fragment.

FEMS Microbiol Lett, 2003 Feb 14, 219(1), 87 - 91
Identification of mixed bacterial DNA contamination in broad-range PCR amplification of 16S rDNA V1 and V3 variable regions by pyrosequencing of cloned amplicons; Grahn N et al.; Using a sensitive and rapid method combining broad-range PCR amplification of bacterial 16S rDNA fragments and pyrosequencing for detection, identification and typing, we have found contaminating bacterial DNA in our reagents used for PCR . Identified bacteria are the water-borne bacterial genera Pseudomonas, Stenotrophomonas, Xanthomonas, Ralstonia and Bacillus . Our results are in concordance with recent reports of contaminated industrial water systems . In light of this conclusion, we believe that there is a need for increased awareness of possible contamination in uncertified widely used molecular biology reagents, including ultra-pure water . Since sequence-based 16S rDNA techniques are used in a variety of settings for bacterial typing and the characterization of microbial communities, we feel that future certification of molecular biology reagents, as free of nucleic acids, would be advantageous.

J Bacteriol, 2003 Mar, 185(5), 1734 - 8
A suppressor of the menadione-hypersensitive phenotype of a Xanthomonas campestris pv . phaseoli oxyR mutant reveals a novel mechanism of toxicity and the protective role of alkyl hydroperoxide reductase; Vattanaviboon P et al.; We isolated menadione-resistant mutants of Xanthomonas campestris pv . phaseoli oxyR (oxyR(Xp)) . The oxyRR2(Xp) mutant was hyperresistant to the superoxide generators menadione and plumbagin and was moderately resistant to H(2)O(2) and tert-butyl hydroperoxide . Analysis of enzymes involved in oxidative-stress protection in the oxyRR2(Xp) mutant revealed a >10-fold increase in AhpC and AhpF levels, while the levels of superoxide dismutase (SOD), catalase, and the organic hydroperoxide resistance protein (Ohr) were not significantly altered . Inactivation of ahpC in the oxyRR2(Xp) mutant resulted in increased sensitivity to menadione killing . Moreover, high levels of expression of cloned ahpC and ahpF in the oxyR(Xp) mutant complemented the menadione hypersensitivity phenotype . High levels of other oxidant-scavenging enzymes such as catalase and SOD did not protect the cells from menadione toxicity . These data strongly suggest that the toxicity of superoxide generators could be mediated via organic peroxide production and that alkyl hydroperoxide reductase has an important novel function in the protection against the toxicity of these compounds in X . campestris.

Theor Appl Genet, 2002 Dec, 106(1), 1 - 8 Epub 2002 Jul 30.
Pyramiding transgenes for multiple resistance in rice against bacterial blight, yellow stem borer and sheath blight; Datta K et al.; Here we describe the development of transgene-pyramided stable elite rice lines resistant to disease and insect pests by conventional crossing of two transgenic parental lines transformed independently with different genes . The Xa21 gene (resistance to bacterial blight), the Bt fusion gene (for insect resistance) and the chitinase gene (for tolerance of sheath blight) were combined in a single rice line by reciprocal crossing of two transgenic homozygous IR72 lines . F4 plant lines carrying all the genes of interest stably were identified using molecular methods . The identified lines, when exposed to infection caused by Xanthomonas oryzae pv oryzae, showed resistance to bacterial blight . Neonate larval mortality rates of yellow stem borer ( Scirpophaga incertulas) in an insect bioassay of the same identified lines were 100% . The identified line pyramided with different genes to protect against yield loss showed high tolerance of sheath blight disease caused by Rhizoctonia solani.

Genetika, 2002 Dec, 38(12), 1656 - 62
{A virulence gene from Xanthomonas campestris pv . campestris homologous to the avrBs2 locus is recognized in race-specific reaction by two different resistance genes in Brassica plant species}; Ignatov AN et al.; Race-specific interaction between the Brassica plants and Xanthomonas compestris pv . campestris bacteria follows the "gene-for-gene" rule . Expression of the avirulence genes recognized by two dominant resistance genes of Brassica, Rxc1 in plants with the BB genome, and Rxc3 in the CC plants, was lost after bacterial mutation in planta . The mutation was distinguished by the elongation of CGCGC pentanucleotide repeat in the gene, which was designated as avrRxc1/3 . This gene displayed strong structural similarity to the avrBs2 locus from the related species X . vesicatoria . Thus, it is the first description of the avrRxc1/3 avirulence gene conferring race-specific interaction between X . campestris pv . campestris and Brassica plants . Structural homologues of the avrBs2 are found in many Xanthomonas species, but in all cases except X . vesicatoria, their function remains unknown.

Wei Sheng Wu Xue Bao, 1999 Aug, 39(4), 339 - 43
{Purification and partial characterization of antagonistic proteins from Bacillus subtilis B034}; Tong Y et al.; Bacillus subtilis B034, an antagonistic bacteria isolated from the phyllosphere of rice, strongly inhibits the growth of Xanthomonas oryzae pv . oryzae which causes the rice bacterial blight . Crude extract was obtained by precipitation of the cell-free culture of B034 with 70% saturated (NH4)2SO4 . The suspension of the precipitate strongly inhibits Xanthomonas oryzae pv . o-ryzae, and it is thermostable, resistant to trypsin, partial sensitive to proteinase K, pronase E and chloroform . Its active pH range is wide, from 4.0 to more than 12.0, relative more stable in high pH . Two antagonistic peaks were obtained from the crude extract of B034 after Phenyl-Sepharose CL-4B, DEAE-Sephacel and FPLC Superdex 75 HR 10/30 column chromatography . One of these two peaks, named P2, was showed only single band with 50.3 kD and pI6.25 in SDS-PAGE and PAGE-IEF, respectively . The N-terminal partial sequence of protein P2 was analyzed.

Wei Sheng Wu Xue Bao, 1998 Aug, 38(4), 251 - 5
{Cloning of DNA sequences involved in exopolysaccharide synthesis of Xanthomonas campestris pv . campestris}; Zha D et al.; By using a cloned DNA segment containing the mutated sequences from the exopolysaccharide-deficient mutant T117 of Xanthomonas campestris pv . campestris as a probe, a 9.4 kb HindIII fragment harbouring DNA sequences corresponding to the mutated site was identified and cloned from the wild-type strain . The fragment could complement the mutant strain T117 in trans and restore the synthesis of exopolysaccharide . This indicates that the fragment contains at least an intact gene which is involved in the exopolysaccharide synthesis of Xanthomonas campestris pv . campestris.

Wei Sheng Wu Xue Bao, 2000 Jun, 40(3), 301 - 5
{Activities of superoxide dismutase in Xanthomonas oryzae pv . oryzae and its induction}; Song F et al.; The activities of superoxide dismutase(SOD) in Xanthomonas oryzae pv . oryzae were determined to demonstrate the correlation of SOD activities with the bacterial virulence . In liquid culture, SOD activities of the tested strains reached the maxima at the end of lag phase and then declined . The virulent strain PXO99A showed higher SOD activities than the avirulent strain PXO99A (pBUavr Xa10.F1) . Analysis on the subcellular location indicated that SOD activities detected from the cytoplasm and periplasm were over 70% and 20%-30% of the total, respectively . Treatment of the bacterial culture for 1 h with exogenous O2- at concentration of 50-800 mumol/L induced SOD activities of both the strains . The treatment with 200 mumol/L resulted in the highest SOD activities . The effect of exogenous O2- on SOD induction was more significant in 12 h-culture than in 24 h-culture, and more notable for the virulent strain PXO99A . The treatment with exogenous O2- resulted in significantly decreased survival rate off both the strains . The decreases of survival rate were greater in 24 h-culture than in 12 h-culture, and more significantly for the virulent strain than for the avirulent one.

Carbohydr Res, 2003 Jan 31, 338(3), 277 - 81
Structural elucidation of the O-chain of the lipopolysaccharide from Xanthomonas campestris strain 8004; Molinaro A et al.; A novel O-specific polysaccharide containing 3-acetamido-3-deoxy-alpha-D-fucose (Fuc3NAc) and D-rhamnose was isolated from the phenol-soluble lipopolysaccharide fraction of the plant associated bacterium Xanthomonas campestris strain 8004 . The structure, determined by means of chemical analysis and 1D and 2D NMR spectroscopy, showed a branched trisaccharide repeating unit, as shown below: {formula: see text}.

Plant J, 2003 Jan, 33(2), 245 - 57
Susceptible to intolerance--a range of hormonal actions in a susceptible Arabidopsis pathogen response; O'Donnell PJ et al.; Ethylene and salicylic acid (SA) are key intermediates in a host's response to pathogens . Previously, we have shown using a tomato compatible interaction that ethylene and SA act sequentially and are essential for disease symptom production . Here, we have examined the relationship between the two signals in the Arabidopsis-Xanthomonas campestris pv . campestris (Xcc) compatible interaction . Preventing SA accumulation by expression of the nahG gene reduced subsequent ethylene production and altered the development of disease symptoms, with plants showing no visible chlorosis . The ethylene insensitive lines, etr1-1 and etr2-1, on the other hand, accumulated SA and exhibited normal but precocious symptom development . Therefore, Arabidopsis, like tomato, was found to exhibit co-operative ethylene and SA action for the production of disease symptoms . However, in Arabidopsis, SA was found to act upstream of ethylene . Jasmonic acid and indole-3-acetic acid levels were also found to increase in response to Xcc . In contrast to ethylene, accumulation of these hormones was not found to be dependent on SA action . These results indicate that the plants response to a virulent pathogen is a composite of multiple signaling pathways.

Curr Microbiol, 2003 Feb, 46(2), 83 - 7
Cloning and characterization of katA, encoding the major monofunctional catalase from Xanthomonas campestris pv . phaseoli and characterization of the encoded catalase KatA; Chauvatcharin N et al.; The first cloning and characterization of the gene katA, encoding the major catalase (KatA), from Xanthomonas is reported . A reverse genetic approach using a synthesized katA-specific DNA probe to screen a X . campestris pv . phaseoli genomic library was employed . A positively hybridizing clone designated pKat29 that contained a full-length katA was isolated . Analysis of the nucleotide sequence revealed an open reading frame of 1,521 bp encoding a 507-amino acid protein with a theoretical molecular mass of 56 kDa . The deduced amino acid sequence of KatA revealed 84% and 78% identity to CatF of Pseudomonas syringae and KatB of P . aeruginosa, respectively . Phylogenetic analysis places Xanthomonas katA in the clade I group of bacterial catalases . Unexpectedly, expression of katA in a heterologous Escherichia coli host resulted in a temperature-sensitive expression . The KatA enzyme was purified from an overproducing mutant of X . campestris and was characterized . It has apparent K(m) and V(max) values of 75 m M {H(2)O(2)} and 2.55 x 10(5) micromol H(2)O(2) micromol heme(-1) s(-1), respectively . The enzyme is highly sensitive to 3-amino-1,2,4-triazole and NaN(3), has a narrower optimal pH range than other catalases, and is more sensitive to heat inactivation.

Planta, 2003 Jan, 216(3), 387 - 96 Epub 2002 Oct 01.
Identification of the pepper SAR8.2 gene as a molecular marker for pathogen infection, abiotic elicitors and environmental stresses in Capsicum annuum; Lee SC et al.; Pepper ( Capsicum annuum L.) SAR8.2 genes, designated CASAR82A, B and C, which are induced by all the biotic and abiotic stresses, were isolated from a pepper cDNA library constructed with the mRNAs from pepper plants infected with Xanthomonas campestris pv . vesicatoria . The pepper CASAR82A, B and C gene products, which are very similar to each other in amino acid sequences, have 43-50% homology with those of tobacco SAR8.2 genes . The CASAR8.2 genes were not constitutively expressed in any of the organs of healthy pepper plants . In contrast, the CASAR82A gene was locally or systemically induced in pepper plants infected by X . campestris pv . vesicatoria, Colletotrichum coccodes or Phytophthora capsici . Strong induction of the CASAR82A gene also was found in pepper leaves treated with ethylene, methyl jasmonate, indole-3-acetic acid, abscisic acid, salicylic acid, benzothiadiazole, DL-beta- n-amino butyric acid or hydrogen peroxide . Interestingly, the transcription of the CASAR82A gene was rapidly triggered by high salinity, drought or low-temperature stresses, but not by mechanical wounding . In situ hybridization results revealed that the CASAR82A mRNAs were localized in phloem and epidermal cells of pepper leaf and stem tissues infected by C . coccodes and P . capsici, or treated with salicylic acid . These results thus suggest that pepper SAR8.2 genes may be valuable as a molecular marker for the detection of various pathogen infections, abiotic elicitors and environmental stresses.

J Gen Appl Microbiol, 1999 Jun, 45(3), 115 - 120
Effect of citric acid on the biosynthesis and composition of xanthan; Jana AK et al.; The effect of citric acid metabolism by Xanthomonas campestris on composition of xanthan has been studied . Citric acid consumption in fed-batch and continuous fermentation increased the pyruvic acid content of xanthan . An increase in pyruvic acid content in xanthan has been explained with the help of energy balance in xanthan biosynthesis.

Acta Crystallogr D Biol Crystallogr, 2003 Jan, 59(Pt 1), 158 - 60 Epub 2002 Dec 19.
X-ray analysis of two antibiotic-synthesizing bacterial ester hydrolases: preliminary results; Barends TR et al.; Alpha-amino-acid ester hydrolases are multimeric enzymes of potential use in antibiotic production . Knowledge of their structure could help to engineer these enzymes into economically viable biocatalysts . The alpha-amino-acid ester hydrolases from Xanthomonas citri and Acetobacter turbidans have been crystallized . The X . citri enzyme crystallizes in a primitive monoclinic space group (unit-cell parameters a = 90.1, b = 125.8, c = 132.1 A, beta = 90.9 degrees ) . The A . turbidans enzyme crystallizes in both a primitive orthorhombic (a = 99.1, b = 104.9, c = 284.9 A) and a body-centred cubic space group with a = b = c = 342.2 A . From both enzymes, diffraction-quality crystals (resolution 3.0 A or better) were obtained . Data-collection statistics are reported for data sets from both enzymes.

Plant Physiol, 2002 Dec, 130(4), 2118 - 28
Cloning and sequencing of cDNAs for hypothetical genes from chromosome 2 of Arabidopsis; Xiao YL et al.; About 25% of the genes in the fully sequenced and annotated Arabidopsis genome have structures that are predicted solely by computer algorithms with no support from either nucleic acid or protein homologs from other species or expressed sequence matches from Arabidopsis . These are referred to as "hypothetical genes." On chromosome 2, sequenced by The Institute for Genomic Research, there are approximately 800 hypothetical genes among a total of approximately 4,100 genes . To test their expression under various growth conditions and in specific tissues, we used six cDNA populations prepared from cold-treated, heat-treated, and pathogen (Xanthomonas campestris pv campestris)-infected plants, callus, roots, and young seedlings . To date, 169 hypothetical genes were tested, and 138 of them are found to be expressed in one or more of the six cDNA populations . By sequencing multiple clones from each 5'- and 3'-rapid amplification of cDNA ends (RACE) product and assembling the sequences, we generated full-length sequences for 16 of these genes . For 14 genes, there was one full-length assembly that precisely supported the intron-exon boundaries of their gene predictions, adding only 5'- and 3'-untranslated region sequences . However, for three of these genes, the other assemblies represent additional exons and alternatively spliced or unspliced introns . For the remaining two genes, the cDNA sequences reveal major differences with predicted gene structures . In addition, a total of six genes displayed more than one polyadenylation site . These data will be used to update gene models in The Institute for Genomic Research annotation database ATH1.

Mol Genet Genomics, 2002 Dec, 268(4), 477 - 87 Epub 2002 Nov 12.
Characterization of Xanthomonas axonopodis pv . citri LexA: recognition of the LexA binding site; Yang MK et al.; Levels of l exA transcripts are markedly increased upon exposure of Xanthomonas axonopodis pathovar citri ( X . a . pv . citri) to the DNA-damaging agent mitomycin C . Preliminary electrophoretic mobility-shift data led us to propose that binding of LexA protein to the sequence upstream of the lexA coding region is responsible for low promoter activity in the uniduced state . We determined that the LexA protein binds to the region located between the transcription start site and the translation initiation codon of the lexA gene of X . a . pv . citri . Using a DNase I footprinting technique, we identified a 19-bp palindromic sequence, TTAGTAGTAATACTACTAA (TTAGN(11)CTAA), located in this region as the binding sequence for the LexA protein of X . a . pv . citri, and showed that the two halves of the palindrome have to be in the inverted repeat orientation to permit binding of LexA . We also showed that almost any mutation in this sequence, including changes in the length of the spacer region of the palindrome, destroyed its ability to bind LexA both in vitro and in vivo.

J Gen Appl Microbiol, 2002 Apr, 48(2), 67 - 76
Rapid cell death in Xanthomonas campestris pv . glycines; Gautam S et al.; Xanthomonas campestris pv . glycines strain AM2 (XcgAM2), the etiological agent of bacterial pustule disease of soybean, exhibited post-exponential rapid cell death (RCD) in LB medium . X . campestris pv . malvacearum NCIM 2310 and X . campestris NCIM 2961 also displayed RCD, though less pronouncedly than XcgAM2 . RCD was not observed in Pseudomonas syringae pv . glycines, or Escherichia coli DH5alpha . Incubation of the post-exponential LB-grown XcgAM2 cultures at 4 degrees C arrested the RCD . RCD was also inhibited by the addition of starch during the exponential phase of LB-growing XcgAM2 . Protease negative mutants of XcgAM2 were found to be devoid of RCD behavior observed in the wild type XcgAM2 . While undergoing RCD, the organism was found to transform to spherical membrane bodies . The presence of membrane bodies was confirmed by using a membrane specific fluorescent label, 1,6-diphenyl 1,3,5-hexatriene (DPH), and also by visualizing these structures under microscope . The membrane bodies of XcgAM2 were found to contain DNA, which was devoid of the indigenous plasmids of the organism . The membrane bodies were found to bind annexin V indicative of the externalization of membrane phosphatidyl serine . Nicking of DNA in XcgAM2 cultures undergoing RCD in LB medium was also detected using a TUNEL assay . The RCD in XcgAM2 appeared to have features similar to the programmed cell death in eukaryotes.

Appl Environ Microbiol, 2002 Dec, 68(12), 6361 - 70
Fingerprinting closely related xanthomonas pathovars with random nonamer oligonucleotide microarrays; Kingsley MT et al.; Current bacterial DNA-typing methods are typically based on gel-based fingerprinting methods . As such, they access a limited complement of genetic information and many independent restriction enzymes or probes are required to achieve statistical rigor and confidence in the resulting pattern of DNA fragments . Furthermore, statistical comparison of gel-based fingerprints is complex and nonstandardized . To overcome these limitations of gel-based microbial DNA fingerprinting, we developed a prototype, 47-probe microarray consisting of randomly selected nonamer oligonucleotides . Custom image analysis algorithms and statistical tools were developed to automatically extract fingerprint profiles from microarray images . The prototype array and new image analysis algorithms were used to analyze 14 closely related Xanthomonas pathovars . Of the 47 probes on the prototype array, 10 had diagnostic value (based on a chi-squared test) and were used to construct statistically robust microarray fingerprints . Analysis of the microarray fingerprints showed clear differences between the 14 test organisms, including the separation of X . oryzae strains 43836 and 49072, which could not be resolved by traditional gel electrophoresis of REP-PCR amplification products . The proof-of-application study described here represents an important first step to high-resolution bacterial DNA fingerprinting with microarrays . The universal nature of the nonamer fingerprinting microarray and data analysis methods developed here also forms a basis for method standardization and application to the forensic identification of other closely related bacteria.

Microbes Infect, 2002 Nov, 4(13), 1361 - 7
Molecular determinants of disease and resistance in interactions of Xanthomonas oryzae pv . oryzae and rice; Shen Y et al.; Xanthomonas oryzae pv . oryzae is the causal agent of rice bacterial blight disease . Numerous genes critical for virulence have been identified . This article reviews current knowledge on the molecular mechanisms of X . oryzae pv . oryzae virulence.

Biochem Biophys Res Commun, 2002 Nov 29, 299(2), 177 - 82
Evaluation of the roles that alkyl hydroperoxide reductase and Ohr play in organic peroxide-induced gene expression and protection against organic peroxides in Xanthomonas campestris; Vattanaviboon P et al.; Alkyl hydroperoxide reductase (ahpC) and organic hydroperoxide resistance (ohr) are distinct genes, structurally and regulatory, but have similar physiological functions . In Xanthomonas campestris pv . phaseoli inactivation of either gene results in increased sensitivity to killing with organic peroxides . An ahpC1-ohr double mutant was highly sensitive to both growth inhibition and killing treatment with organic peroxides . High level expression of ahpC or ohr only partially complemented the phenotype of the double mutant, suggesting that these genes function synergistically, but through different pathways, to protect Xanthomonas from organic peroxide toxicity . Functional analyses of Ohr and AhpC abilities to degrade organic hydroperoxides revealed that both Ohr and AhpC could degrade tert-butyl hydroperoxide (tBOOH) while the former was more efficient at degrading cumene hydroperoxide (CuOOH) . Expression analysis of these genes in the mutants showed no compensatory alterations in the levels of AhpC or Ohr . However, CuOOH induced expression of these genes in the mutants was affected . CuOOH induced ahpC expression was higher in the ohr mutant than in the parental strain; in contrast, the ahpC mutation has no effect on the level of induced ohr expression . These analyses reveal complex physiological roles and expression patterns of seemingly functionally similar genes.

Mol Plant Microbe Interact, 2002 Oct, 15(10), 983 - 9
Ectopic expression of Tsi1 in transgenic hot pepper plants enhances host resistance to viral, bacterial, and oomycete pathogens; Shin R et al.; In many plants, including hot pepper plants, productivity is greatly affected by pathogen attack . We reported previously that tobacco stress-induced gene 1 (Tsi1) may play an important role in regulating stress responsive genes and pathogenesis-related (PR) genes . In this study, we demonstrated that overexpression of Tsi1 gene in transgenic hot pepper plants induced constitutive expression of several PR genes in the absence of stress or pathogen treatment . The transgenic hot pepper plants expressing Tsi1 exhibited resistance to Pepper mild mottle virus (PMMV) and Cucumber mosaic virus (CMV) . Furthermore, these transgenic plants showed increased resistance to a bacterial pathogen, Xanthomonas campestris pv . vesicatoria and also an oomycete pathogen, Phytophthora capsici . These results suggested that ectopic expression of Tsi1 in transgenic hot pepper plants enhanced the resistance of the plants to various pathogens, including viruses, bacteria, and oomycete . These results suggest that using transcriptional regulatory protein genes may contribute to developing broad-spectrum resistance in crop plants.

Meded Rijksuniv Gent Fak Landbouwkd Toegep Biol Wet, 2001, 66(2a), 233 - 40
Dominance relationships of bean pathogens at Lake Balaton; Balazs A et al.; Dominance relationships of different bean pathogens were examined during 1999-2000 in small plot trials at Lake Balaton in Hungary . In 1999 the dominant pathogen species were Xanthomonas campestris pv . phaseoli . The main cause of the stock decay was due to the infection of Fusarium spp . Bean plants were infected also by Alternaria, Colletotrichum, Macrophomina and Sclerotinia, species part from viruses . Among of thirty-eight examined bean cultivars and genotypes the variety "Diszbab" and the genotype 513 were the most resistant . In 2000 Macrophomina phaseolina and Fusarium spp . caused epidemics . Most of the observed plants died early . The most healthy species and branches were the SC-34-1 and cv . Diszbab.

Carbohydr Res, 2002 Oct 11, 337(19), 1723 - 8
Structures of the O-polysaccharide chains of the lipopolysaccharides of Xanthomonas campestris pv phaseoli var fuscans GSPB 271 and X campestris pv malvacearum GSPB 1386 and GSPB 2388; Senchenkova SN et al.; O-polysaccharides of phytopathogenic bacteria Xanthomonas campestris were isolated by mild acid degradation of the lipopolysaccharides and studied by sugar and methylation analysis, along with 1H and 13C NMR spectroscopy . The following structures of the repeating units of the polysaccharides of X . campestris pv . phaseoli var . fuscans GSPB 271 (1) . and X . campestris pv . malvacearum GSPB 1386 and GSPB 2388 (2) . were established:The O-polysaccharides of X . campestris are structurally similar to those of some Pseudomonas syringae strains.

Mol Microbiol, 2002 Nov, 46(3), 637 - 47
A high-molecular-weight outer membrane protein of Xanthomonas oryzae pv . oryzae exhibits similarity to non-fimbrial adhesins of animal pathogenic bacteria and is required for optimum virulence; Ray SK et al.; Transposon insertions in a novel 3.798 kb open reading frame (ORF) of the rice pathogen, Xanthomonas oryzae pv . oryzae (Xoo) cause virulence deficiency and altered colony/lawn morphology . This ORF encodes a protein, XadA, of 1,265 amino acids that exhibits significant similarity to non-fimbrial adhesins of animal pathogenic bacteria such as Yersinia YadA and Moraxella UspA1 . An interesting feature is that the YadA similarity region is repeated six times within the XadA sequence and encompasses almost the entire length of the protein . Anti-XadA antibodies identified a 110 kDa outer membrane protein that was sensitive to protease treatment of whole cells . XadA expression is induced in minimal medium . Homology modelling suggests that XadA adopts a beta-helix conformation-like pertactin, a non-fimbrial adhesin of Bordetella pertussis . This work is the first characterization of a non-fimbrial adhesin-like molecule in a plant pathogenic bacterium . It extends our knowledge about the repertoire of homologous virulence factors that are deployed by animal and plant pathogenic bacteria to include functions potentially involved in adhesion.

Mol Genet Genomics, 2002 Oct, 268(2), 253 - 61 Epub 2002 Aug 27.
Fine genetic mapping and physical delimitation of the lesion mimic gene Spl11 to a 160-kb DNA segment of the rice genome; Zeng L et al.; The rice lesion mimic mutant spl11 was previously found to confer broad-spectrum disease resistance to both Magnaporthe grisea and Xanthomonas oryzae pv . oryzae . To better understand the molecular basis underlying cell death and disease resistance in rice, a map-based cloning strategy has been employed to isolate Spl11 . Five Spl11-linked RAPD markers were developed and four of them were mapped to rice chromosome 12 . A high-resolution genetic map was developed using a segregating population consisting of 1138 lesion mimic individuals . Recombination suppression was observed in the vicinity of Spl11 . Three molecular markers tightly linked to Spl11 were identified and used to screen a BAC library . A contig spanning the Spl11 locus was constructed and physical mapping delimited Spl11 to a 160-kb DNA segment within a single BAC clone . These results provide the essential information for the final isolation of this important gene in the rice defense pathway.

FEMS Microbiol Lett, 2002 Sep 24, 215(1), 23 - 31
Characterization of pathogenic and nonpathogenic strains of Xanthomonas axonopodis pv . manihotis by PCR-based DNA fingerprinting techniques; Gonzalez C et al.; Strains of Xanthomonas axonopodis pv . manihotis (Xam) were characterized for pathogenicity and for DNA polymorphism using different PCR-based techniques . Using amplified restriction fragment length polymorphism (AFLP), strains were distinguished from each other and also from other Xanthomonas strains . Cluster analysis showed a high correlation between DNA polymorphism and pathogenicity . Four Xam strains were further analyzed using three PCR-based techniques, AFLP, AFLP-pthB and RAPD-pthB . Various primer combinations were used including primers specific to a Xam pathogenicity gene (pthB) along with RAPD or AFLP primers . The AFLP primer combinations EcoRI+T/MseI+A and EcoRI+T/MseI+T were the most efficient to discriminate among pathogenic and nonpathogenic Xam strains . Polymorphic bands were excised from the gel, amplified and cloned . Sequences analysis showed significant homology with bacterial pathogenicity island, genes involved in pathogenic fitness and regulators of virulence . Three cloned AFLP fragments were used as probes in DNA blot experiments and two of them showed significant polymorphism.

Lett Appl Microbiol, 2002, 35(5), 375 - 9
Isolation of a Xanthomonas campestris strain with elevated beta-galactosidase activity for direct use of lactose in xanthan gum production; Yang TC et al.; AIMS: To isolate a Xanthomonas campestris strain that can use lactose directly for xanthan gum production . METHODS AND RESULTS: The presence of indigenous beta-galactosidase gene in the wild-type Xc17 was detected by PCR and Southern hybridization . Treatment of Xc17 with nitrous acid resulted in the isolation of Xc17L with a 3.5-fold elevation of beta-galactosidase activity capable of growing in lactose-based medium . Xc17L is stable for at least 100 generations in terms of beta-galactosidase expression . The amounts of xanthan produced by Xc17L in lactose-based medium are comparable to those in glucose-based medium . CONCLUSIONS: Xc17L is potentially useful for xanthan production from whey, a waste containing lactose . SIGNIFICANCE AND IMPACT OF THE STUDY: A lactose-utilizing strain of X . campestris strain can be constructed without incorporation of any exotic DNA or antibiotic resistance gene and therefore concern of a gene-modified organism and fear of a spread of an antibiotic-resistant gene are avoided.

IUBMB Life, 2002 Jul, 54(1), 13 - 8
Isolation and characterization of a porin-like outer membrane protein from Xanthomonas campestris pv . campestris; Wang L et al.; Xanthomonas campestris pv . campestris, a plant-associated pathogenic bacterium, is the causal agent of foliar spots and blights in crucifers . The major outer membrane protein, Omp37, of 37 kDa, has been identified, purified to homogeneity, and its characterization has also been carried out . Native Omp37 behaved as a trimer, as revealed by gel filtration and SDS-PAGE . FTIR measurements revealed a high beta-structure content . The pore-forming ability of the purified Omp37 was studied by the liposome swelling assay . Omp37, to our knowledge, is the first porin that has been isolated from Xanthomonas . This study clearly demonstrates that Omp37 is related to the family of trimeric bacterial porins.

J Biotechnol, 2002 Nov 13, 99(3), 307 - 17
The influence of metabolic network structures and energy requirements on xanthan gum yields; Letisse F et al.; The metabolic network of Xanthomonas campestris is complex since a number of cyclic pathways are present making simple stoichiometric yield predictions difficult . The influence of certain pathway configurations and the resulting variations in flux have been examined as regards the maximum yield potential of this bacteria for xanthan gum production . These predictions have been compared with experimental results showing that the strain employed is functioning close to its theoretical maximum as regards yield criteria . The major constraint imposed on the network concerns energy availability which has a more pronounced effect on yield than carbon precursor supply . This can be attributed to the relatively high maintenance requirements determined experimentally and incorporated into the model . While some of this overall energy burden will undoubtedly be associated with incompressible metabolic requirements such as sugar uptake and xanthan efflux mechanisms, future strain improvement strategies will need to attack other non-essential energy-consuming reactions, if yields are to be further increased.

EMBO J, 2002 Oct 15, 21(20), 5313 - 22
Getting across--bacterial type III effector proteins on their way to the plant cell; Buttner D et al.; Pathogenicity of most Gram-negative bacterial plant pathogens depends on hrp (hypersensitive response and pathogenicity) genes, which control the ability to cause disease and to elicit specific defense responses in resistant plants . hrp genes encode a specialized type III secretion (TTS) system that mediates the vectorial delivery of bacterial effector proteins across both bacterial membranes as well as across the eukaryotic plasma membrane into the host cell cytosol . One well-studied effector protein is AvrBs3 from Xanthomonas campestris pv . vesicatoria, the causal agent of bacterial spot in pepper and tomato . AvrBs3 induces hypertrophy symptoms in susceptible plants and triggers a resistance gene-specific cell death reaction in resistant plants . Intriguingly, AvrBs3 has characteristic features of eukaryotic transcription factors, suggesting that it modulates the host's transcriptome . Here, we discuss the TTS system of X.campestris pv . vesicatoria in the light of current knowledge on type III-dependent protein secretion in plant pathogenic bacteria.

Mol Microbiol, 2002 Oct, 46(1), 13 - 23
Type III-dependent translocation of the Xanthomonas AvrBs3 protein into the plant cell; Szurek B et al.; Many plant pathogenic bacteria utilize a conserved type III secretion system (TTSS) to deliver effector proteins into the host tissue . Indirect evidence has suggested that at least some effector proteins are translocated from the bacterial cytoplasm into the plant cell . Using an immunocytochemical approach, we demonstrate that the type III effector AvrBs3 from Xanthomonas campestris pv . vesicatoria localizes to nuclei of infected pepper leaves . Importantly, AvrBs3 translocation was observed in situ in native tissues of susceptible and resistant plants . AvrBs3 was detected in the nucleus as soon as 4 h post infection, which was dependent on a functional TTSS and the putative translocator HrpF . N-terminal AvrBs3 deletion derivatives are no longer secreted by the TTSS in vitro and could not be detected inside the host cells, suggesting that the N-terminus of AvrBs3 is important for secretion . Deletion of the nuclear localization signals in the AvrBs3 C-terminus, which are required for the AvrBs3-mediated induction of the hypersensitive reaction in resistant pepper plants, abolished AvrBs3 localization to the nucleus . This is the first report on direct evidence for translocation of a native type III effector protein from a plant pathogenic bacterium into the host cell.

Plant J, 2002 Oct, 32(1), 1 - 12
Lipid peroxidation in cotton: Xanthomonas interactions and the role of lipoxygenases during the hypersensitive reaction; Jalloul A et al.; Lipid peroxidation, often associated with hypersensitive cell death, may be initiated either by active oxygen species (AOS) or lipoxygenases (LOX) . Here we report a detailed analysis of this oxidative process in both incompatible and compatible interactions between the cotton cultivar Reba B50 and Xanthomonas campestris pv . malvacearum (Xcm) . The hypersensitive reaction (HR) was characterized by a massive production of polyunsaturated fatty acid (PUFA) hydroperoxides together with typical tissue dehydration . Among these, isomers peroxidized on carbon 9, largely predominant, were chiral, showing an excess in the S enantiomer . The HR process was accompanied by an increase in 9S-LOX activity and preceded by transcription of a LOX gene (GhKLox1) . These results showed that: (i) AOS produced during the oxidative burst were not involved in PUFA peroxidation during HR; and (ii) as previously described in elicited leaves of tobacco, the massive enzymatic lipid peroxidation was closely associated with hypersensitive cell death . During disease development in this cotton cultivar, the 9-lipoxygenation of PUFAs was late, weak, preceded by a faint accumulation of GhKLox1 transcripts, and associated with chlorosis but not with necrosis . Consequently, the main difference between incompatible and compatible interactions was in the precocity and intensity of the oxidative process, rather than in its nature . These data provide the evidence for a correlation between lipid peroxidation and hypersensitive cell death induced by pathogens.

Biochem Biophys Res Commun, 2002 Oct 4, 297(4), 968 - 73
Transaldolase exhibits a protective role against menadione toxicity in Xanthomonas campestris pv . phaseoli; Vatanaviboon P et al.; A talA gene encoded transaldolase, a rate-limiting enzyme in the non-oxidative branch of the pentose-phosphate pathway, was cloned from Xanthomonas campestris pv . phaseoli . talA located in a region of the bacterial genome rich in genes involved in oxidative stress protection and regulation . TalA from X . campestris pv . phaseoli showed a high degree of homology to many previously reported transaldolases from both prokaryotic and eukaryotic sources . The expression of X . campestris pv . phaseoli talA was high at log-phase of growth, then declined at stationary phase, and could not be induced by oxidants . A talA mutant constructed by insertional inactivation did not possess any detectable transaldolase activity . Lack of a functional talA gene did not affect bacterial growth in a rich medium containing glucose or sucrose as a carbon source . However, the talA knockout mutant showed increased sensitivity to the superoxide generator menadione, but not to other oxidants . This increased menadione sensitivity phenotype could be complemented by expression of talA in a plasmid vector . The data demonstrated a novel and essential role of transaldolase in protection against menadione toxicity in X . campestris.

Mol Microbiol, 2002 Sep, 45(6), 1647 - 54
OhrR, a transcription repressor that senses and responds to changes in organic peroxide levels in Xanthomonas campestris pv . phaseoli; Panmanee W et al.; We report the physiological role of OhrR as an organic peroxide sensor and transcription repressor in Xanthomonas campestris pv . phaseoli . In vivo exposure of X . campestris pv . phaseoli to either tert-butyl or cumene hydroperoxides efficiently neutralized OhrR repression of expression from the OhrR-regulated P1 promoter . H2O2 was a weak and non-physiological inducer of the system while other oxidants and metabolites of organic peroxide metabolism did not induce the expression from the P1 . Northern blotting results indicated a correlation between concentrations of tert-butyl hydroperoxide used in the treatment and the induction of ohr (an OhrR-regulated gene) expression . In addition, the levels of ohr mRNA in cultures induced by various concentrations of tert-butyl hydroperoxide were reduced in cells with high levels of an organic peroxide metabolising enzyme (AhpC-AhpF) but not in cells with high catalase levels suggesting that organic peroxide interacts with OhrR . DNA band shift experiments using purified OhrR and the P1 promoter fragment showed that organic peroxide treatment prevented binding of the protein to the P1 promoter by oxidation of OhrR, as the inhibition of binding to the P1 promoter was reversed by addition of a reducing agent, DTT . The highly conserved cysteine residue C22 of OhrR is required for organic peroxide inducible gene expression . A mutant protein, OhrRC22S can repress the P1 promoter activity but is insensitive to organic peroxide treatment . Thus, OhrR is the first transcription repressor characterized that appeared to evolve to physiologically sense organic peroxides.

Plant Cell, 1992 Jan, 4(1), 79 - 86
A Xanthomonas Pathogenicity Locus Is Induced by Sucrose and Sulfur-Containing Amino Acids; Schulte R et al.; Expression of hrp (hypersensitive reaction and pathogenicity) genes from Xanthomonas campestris pv vesicatoria is suppressed in complex media but induced in the plant . We examined the effects of macronutrients on transcription of hrp-gusA ({beta}-glucuronidase) fusions by growth of the bacteria in defined medium . Modified MM1 minimal medium, supplemented with casamino acids, was able to induce hrpF strongly when sucrose or fructose was added as a carbon source . However, high concentrations of casamino acids suppressed hrpF induction . Sulfur-containing amino acids were required for induction, with methionine induction being comparable to induction in plants . Both sucrose and methionine were required for induction . Induction in medium optimal for hrpF induction, designated XVM1, occurred at pH 5.5 to pH 7.5 . High concentrations of phosphate or sodium chloride suppressed gene activation . Gene induction was inhibited by succinate, citrate, pyruvate, and glutamine . Expression levels of different hrp loci from X . c . vesicatoria in XVM1 varied, dependent on the genetic background of the Xanthomonas strain used . The results suggest that several control mechanisms might be involved in the expression of hrp genes.

Mol Cells, 2002 Aug 31, 14(1), 75 - 84
A hot pepper cDNA encoding ascorbate peroxidase is induced during the incompatible interaction with virus and bacteria; Yoo TH et al.; Capsicum annuum L . is infected by a number of viruses, including the tobacco mosaic virus (TMV) . To study the defense-related genes that are induced by TMV in hot peppers, the pepper plant, which is susceptible to P1.2 but resistant to the P0 pathotype of TMV, was inoculated with TMV-P0 . Differential screening isolated the genes that were specifically up- or down-regulated during the hypersensitive response (HR) . The CaAPX1 cDNA clone that putatively encodes a polypeptide of cytosolic ascorbate peroxidase was selected as an up-regulated gene . It was isolated for further study . The full-length cDNA for CaAPX1, which is 972 bp long, contained the open-reading frame of 250-amino acid residues . A genomic Southern blot analysis showed that there were only limited copies of the CaAPX1 gene in the hot pepper genome . In hot pepper cv . Bugang, which is resistant to TMV-P0 and susceptible to TMV-P1.2, the CaAPX1 gene transcript was accumulated by TMV-P0, but not by TMV-P1.2 inoculation . CaAPX1 transcripts began to accumulate 24 h post-inoculation of TMV-P0, and increased gradually until 96 h . To investigate whether each transcript is induced by other stimuli, the plants were treated with various chemicals and wounding . A striking induction of the CaAPX1 transcript was observed at 2 h . It subsided 12 h after salicylic acid (SA), ethephon, and methyl jasmonate (MeJA) treatments . The response of the gene upon other pathogen infection was also examined by a bacterial pathogen (Xanthomonas campestris pv . vesicatoria race 3) inoculation . The CaAPX1 gene was induced in a hot pepper (C . annuum cv . ECW 20R) that was resistant to this bacterial pathogen, but not in a susceptible hot pepper (C . annuum cv . ECW) . These results suggest the possible role(s) for the CaAPX1 gene in plant defense against viral and bacterial pathogen.

Plant Cell, 1996 Jun, 8(6), 1079 - 1090
Changes in the Plasma Membrane Distribution of Rice Phospholipase D during Resistant Interactions with Xanthomonas oryzae pv oryzae; Young SA et al.; Phospholipase D (PLD; EC 3.1.4.4), which hydrolyzes phospholipids to generate phosphatidic acid, was examined in rice leaves undergoing susceptible or resistant interactions with Xanthomonas oryzae pv oryzae . RNA analysis of leaves undergoing resistant interactions revealed different expression patterns for PLD over 5 days relative to control plants or those undergoing susceptible interactions . By using an activity assay and immunoblot analysis, we identified three forms of PLD (1, 2, and 3) . PLD 1 was observed only at 1 day after tissue infiltration . PLDs 2 and 3 were detected up to 3 days in all interactions . Immunoelectron microscopy studies revealed PLD to be associated predominantly with the plasma membrane . In cells undergoing a susceptible response, PLD was uniformly distributed along the plasma membrane at 3, 6, 12, and 24 hr after inoculation . However, within 12 hr after bacterial challenge in resistant interactions, PLD was clustered preferentially in membranes adjacent to bacterial cells.

Res Microbiol, 2002 Jul-Aug, 153(6), 345 - 51
Gluconacetobacter diazotrophicus, a sugar cane endosymbiont, produces a bacteriocin against Xanthomonas albilineans, a sugar cane pathogen; Pinon D et al.; Gluconacetobacter diazotrophicus in liquid culture secretes proteins into the medium . Both medium containing Gluconacetobacter protein and a solution of this protein after acetone precipitation appeared to inhibit the growth of Xanthomonas albilineans in solid culture . This apparent inhibition of bacterial growth has, in fact, been revealed to be lysis of bacterial cells, as demonstrated by transmission electron microscopy . Fractionation of the Gluconacetobacter protein mixture in size-exclusion chromatography reveals a main fraction with lysozyme-like activity which produces lysis of both living bacteria and isolated cell walls.

Appl Environ Microbiol, 2002 Sep, 68(9), 4173 - 81
Biodegradation of the polyketide toxin cercosporin; Mitchell TK et al.; Cercosporin is a non-host-specific polyketide toxin produced by many species of plant pathogens belonging to the genus Cercospora . This red-pigmented, light-activated toxin is an important pathogenicity determinant for Cercospora species . In this study, we screened 244 bacterial isolates representing 12 different genera for the ability to degrade cercosporin . Cercosporin degradation was determined by screening for the presence of cleared zones surrounding colonies on cercosporin-containing culture medium and was confirmed by assaying the kinetics of degradation in liquid medium . Bacteria belonging to four different genera exhibited the cercosporin-degrading phenotype . The isolates with the greatest cercosporin-degrading activity belonged to Xanthomonas campestris pv . zinniae and X . campestris pv . pruni . Isolates of these pathovars removed over 90% of the cercosporin from culture medium within 48 h . Bacterial degradation of red cercosporin was accompanied by a shift in the color of the growth medium to brown and then green . The disappearance of cercosporin was accompanied by the appearance of a transient green product, designated xanosporic acid . Xanosporic acid and its more stable lactone derivative, xanosporolactone, are nontoxic to cercosporin-sensitive fungi and to plant tissue and are labile in the presence of light . Detailed spectroscopic analysis (to be reported in a separate publication) of xanosporolactone revealed that cercosporin loses one methoxyl group and gains one oxygen atom in the bacterial conversion . The resulting chromophore (4,9-dihydroxy-3-oxaperlylen-10H-10-one) has never been reported before but is biosynthetically plausible via oxygen insertion by a cytochrome P-450 enzyme.

Eur J Biochem, 2002 Sep, 269(17), 4185 - 93
NMR and MS evidences for a random assembled O-specific chain structure in the LPS of the bacterium Xanthomonas campestris pv . Vitians . A case of unsystematic biosynthetic polymerization; Molinaro A et al.; Xanthomonas campestris pv . vitians is a Gram-negative plant-associated bacterium that acts as causative agent of bacterial leaf spot and headrot in lettuce . The lipopolysaccharide of this bacterium is suspected to be an important molecule for adhesion to and infection of the plants . The lipopolysaccharide has been isolated from the phenol phase and the O-specific chain characterized by compositional analysis, high field NMR and MALDI-TOF MS . It consists of a nonrepetitive branched polysaccharide with a rhamnan backbone to which Fuc3NAc is linked . The NMR and MS approach led to the characterization of the fine structure of the polymer, which is randomly assembled . The rhamnan backbone is built up of beta-Rhap and alpha-Rhap, this last is present in one, two or three adjacent units and branched by an alpha-Fucp3NAc unit . This is a real case of a random constituted O-specific chain, therefore biosynthetic studies towards the comprehension of this irregular biosynthesis are needed.

Water Res, 2002 Jul, 36(13), 3211 - 8
Characterization of an acetate-degrading sludge without intracellular accumulation of polyphosphate and glycogen; Fang HH et al.; A sequencing batch reactor (SBR) was operated in the conventional anaerobic-aerobic mode for enhanced biological phosphate removal (EBPR) using acetate as the sole substrate . Results showed that, however, the reactor was unable to remove phosphate from wastewater . The sludge containing 1.65% of phosphate did not exhibit the typical characteristics of polyphosphate-accumulating organisms (PAO) or glycogen-accumulating organisms (GAO) . Phylogenetic analysis, based on 16S rDNA sequences of individual microorganisms, showed that the microbial community of this acetate-degrading sludge was closely related to Comamonas testosteroni (43.8% of total population) of beta-1-proteobacteria, Zoogloea resiniphila (25.0%) of beta-2-proteobacteria, and Xanthomonas maltophilia (19.8%) of gamma-proteobacteria . Results of this study imply that GAO might not be the sole group of bacteria responsible to the deterioration of phosphate removal efficiency in an EBPR reactor.

Genome, 2002 Aug, 45(4), 670 - 8
RAPD-based genetic linkage maps of yellow passion fruit (Passiflora edulis Sims . f . flavicarpa Deg.); Carneiro MS et al.; A single cross between two clones of passion fruit (Passiflora edulis Sims . f . flavicarpa Deg., 2n = 18) was selected for genetic mapping . The mapping population was composed of 90 F1 plants derived from a cross between 'IAPAR 123' (female parent) and 'IAPAR 06' (male parent) . A total of 380 RAPD primers were analyzed according to two-way pseudo-testcross mapping design . The linkage analysis was performed using Mapmaker version 3.0 with LOD 4.0 and a maximum recombination fraction (theta) of 0.30 . Map distances were estimated using the Kosambi mapping function . Linkage maps were constructed with 269 loci (2.38 markers/primer), of which 255 segregated 1:1, corresponding to a heterozygous state in one parent and null in the other . The linkage map for 'IAPAR123' consisted of 135 markers . A total of nine linkage groups were assembled covering 727.7 cM, with an average distance of 11.20 cM between framework loci . The sizes of the linkage groups ranged from 56 to 144.6 cM . The linkage map for 'IAPAR 06' consisted of 96 markers, covering 783.5 cM . The average distance between framework loci was 12.2 cM . The length of the nine linkage groups ranged from 20.6 to 144.2 cM . On average, both maps provided 61% genome coverage . Twenty-four loci (8.9%) remained unlinked . Among their many applications, these maps are a starting point for the identification of quantitative trait loci for resistance to the main bacterial disease affecting passion fruit orchards in Brazil, caused by Xanthomonas campestris pv . passiflorae, because parental genotypes exhibit diverse responses to bacterial inoculation.

Sheng Wu Gong Cheng Xue Bao, 2002 Jan, 18(2), 182 - 6
{Cloning of Xanthomonas campestris pv . campestris pathogenicity-related gene sequences by TAIL-PCR}; Ying G et al.; Southern blot analysis with probe from mini-Tn5 gfp-km transposon indicated that 5 non-pathogenic mutants which were generated by insertion of mini-Tn5 gfp-km mutagenesis contained a single copy of the transposon . Using genomic DNA of each mutant as a template, TAIL-PCR was performed with seven arbitrary degenerate (AD) primers pairing with 3 nested specific primers designed based on the sequence of GFP toward outside in mini-Tn5 gfp-km . After 3-step PCR reactions, the flanking sequence of each mutant was obtained . The PCR product was ligated with pGEM-T EASY vector and then was transformed into E . coli DH5 alpha by electroporation . Positive clones were selected by white/blue colony and plasmid was isolated, then digested with EcoRI . Plasmid was sequenced if its insert was longer than 300 bp . Our results indicated that TAIL-PCR was proved to be a simple and efficient approach in identification of gene using insertion mutagenesis.

Biochem J, 2002 Nov 1, 367(Pt 3), 865 - 71
A reversibly dissociable ternary complex formed by XpsL, XpsM and XpsN of the Xanthomonas campestris pv . campestris type II secretion apparatus; Tsai RT et al.; The cytoplasmic membrane proteins XpsL, XpsM and XpsN are components required for type II secretion in Xanthomonas campestris pv . campestris . We performed metal-chelating chromatography to partially purify the His(6)-tagged XpsM (XpsMh)-containing complex . Immunoblot analysis revealed that both XpsL and XpsN co-eluted with XpsMh . The co-fractionated XpsL and XpsN proteins co-immune precipitated with each other, suggesting the existence of an XpsL-XpsM-XpsN complex . Ternary complex formation does not require other Xps protein components of the type II secretion apparatus . Further purification upon size-exclusion chromatography revealed that XpsN is prone to dissociate from the complex . Reassociation of XpsN with the XpsL-XpsMh complex immobilized on a nickel column is more effective than with XpsMh alone . Membrane-mixing experiments suggested that the XpsL-XpsMh complex and XpsN probably dissociate and reassociate in the membrane vesicles . Comparison of the half-lives of the XpsL-XpsMh-XpsN and XpsL-XpsMh complexes revealed that XpsL dissociates from the latter at a faster rate than from the former . Dissociation and reassociation between XpsL and XpsM were also demonstrated with membrane-mixing experiments . A dynamic model is proposed for the XpsL-XpsM-XpsN complex.

Biochem Biophys Res Commun, 2002 Jul 5, 295(1), 43 - 9
Transcription of Xanthomonas campestris prt1 gene encoding protease 1 increases during stationary phase and requires global transcription factor Clp; Hsiao YM et al.; Xanthomonas campestris pv . campestris produces three proteases, Prt1, Prt2, and Prt3, the first two of which are involved in pathogenicity . In this study, nucleotide A 84 nt upstream of the prt1 start codon, which is 8 nt downstream of the -10 sequence, was determined as the transcription start site by the 5(') RACE (rapid amplification of cDNA ends) method . Using Pprt1-lacZ transcriptional fusion constructs for assays, several interesting characteristics of prt1 promoter were revealed . The expression is inducible by LB medium or casein proteins and involves the global transcription factor Clp (cyclic AMP receptor protein-like protein) . The region containing bp -392 to -80 relative to the prt1 translation initiation codon is required for maximal expression, in which bp -392 to -207 responds to the Clp-mediated regulation and the induction . In presence of inducers and the clp wild-type background, the levels of expression continue to increase following cell growth until 30 h after the cultures entering stationary phase . Since prt1 promoter shows no response to stressful conditions and neither growth nor cell viability is affected by prt1 mutation, Prt1 appears to be a secondary metabolite of X . campestris pv . campestris . (c) 2002 Elsevier Science (USA).

J Mol Biol, 2002 Jun 28, 320(1), 11 - 22
A novel bacteriophage-encoded RNA polymerase binding protein inhibits transcription initiation and abolishes transcription termination by host RNA polymerase; Nechaev S et al.; Xp10 is a lytic bacteriophage of Xanthomonas oryzae, a Gram-negative bacterium that causes rice blight . We purified an Xp10 protein, p7, that binds to and inhibits X . oryzae RNA polymerase (RNAP) . P7 is a novel 73 amino acid-long protein; it does not bind to and hence does not affect transcription by Escherichia coli RNAP . Analysis of E . coli/X . oryzae RNAP hybrids locates the p7 binding site to the largest X . oryzae RNAP subunit, beta' . Binding of p7 to X . oryzae RNAP holoenzyme prevents large conformational change that places the sigma subunit region 4 into the correct position for interaction with the -35 promoter element . As a result, open promoter complex formation on the -10/-35 class promoters is inhibited . Inhibition of promoter complex formation on the extended -10 class promoters is less efficient . The p7 protein also abolishes factor-independent transcription termination by X . oryzae RNAP by preventing the release of nascent RNA at terminators . Further physiological and mechanistic studies of this novel transcription factor should provide additional insights into its biological role and the processes of promoter recognition and transcription termination . (c) 2002 Elsevier Science Ltd.

Proc Natl Acad Sci U S A, 2002 Jun 11, 99(12), 8336 - 41
Direct biochemical evidence for type III secretion-dependent translocation of the AvrBs2 effector protein into plant cells; Casper-Lindley C et al.; The calmodulin-dependent adenylate cyclase domain (Cya) of the Bordetella pertussis cyclolysin was used as a reporter protein to study the direct translocation of the Xanthomonas effector protein, AvrBs2, into the plant host cell . Adenylate cyclase activity (production of cAMP) depends on the presence of eukaryotic plant calmodulin and is only active after translocation from the prokaryotic cell into the eukaryotic plant cell . Here, we show that infection of pepper plants by Xanthomonas campestris pv . vesicatoria strains expressing the AvrBs2:Cya fusion protein results in detectable increases of cAMP levels in plant cells as early as 3 h after inoculation . Adenylate cyclase activity was shown to be type III secretion-dependent as the Xanthomonas hrp mutations, hrcV or hrpF, failed to produce detectable levels of cAMP in infected pepper plants . Furthermore, the N-terminal secretion and translocation signals of AvrBs2 were shown to be required for activity of the fusion protein in the plant . A single genomic copy of the avrBs2:cya fusion gene expressed under the control of the wild-type avrBs2 promoter was used to compare the effect of a susceptible and resistant plant interaction on the kinetics of effector protein delivery . Implications of these results and additional applications of this reporter construct are discussed.

Mol Plant Microbe Interact, 2002 Jun, 15(6), 540 - 8
PPI1: a novel pathogen-induced basic region-leucine zipper (bZIP) transcription factor from pepper; Lee SJ et al.; We have isolated a full-length cDNA, PPI1 (pepper-PMMV interaction 1), encoding a novel basic region-leucine zipper (bZIP) DNA-binding protein, from expressed sequence tags differentially expressed in Capsicum chinense P1257284 infected with Pepper mild mottle virus (PMMV) . PPI1 encodes a predicted protein of 170 amino acids and contains a putative DNA-binding domain that shares significant amino acid identity with ACGT-binding domains of members of the bZIP DNA-binding protein family . PPI1 was localized in the nucleus and had transcriptional activation activity in yeast . Transcripts of the PPI1 gene were preferentially induced during an incompatible interaction by inoculation with PMMV, Pseudomonas syringae pv . syringae 61, and Xanthomonas campestris pv . vesicatoria race 3 . However, the PPII gene was not induced by abiotic stressors that activate the plant defense-signaling pathway . Our data provide the first evidence that a bZIP transcription factor is preferentially induced by pathogen attack, suggesting that PPI1 may play a specific functional role in the regulation of expression of plant defense-related genes.

J Bacteriol, 2002 Jul, 184(13), 3539 - 48
Genetic locus encoding functions involved in biosynthesis and outer membrane localization of xanthomonadin in Xanthomonas oryzae pv . oryzae; Goel AK et al.; Xanthomonadins are membrane-bound, brominated, aryl-polyene pigments specific to the genus Xanthomonas . We have characterized a genetic locus (pig) from Xanthomonas oryzae pv . oryzae which contains four open reading frames (ORFs) that are essential for xanthomonadin production . Three of these ORFs are homologous to acyl carrier proteins, dehydratases, and acyl transferases, suggesting a type II polyketide synthase pathway for xanthomonadin biosynthesis . The fourth ORF has no homologue in the database . For the first time, we report that a putative cytoplasmic membrane protein encoded in the pig locus is required for outer membrane localization of xanthomonadin in X . oryzae pv . oryzae . We also report the identification of a novel 145-bp palindromic Xanthomonas repetitive intergenic consensus element that is present in two places in the pig locus . We estimate that more than 100 copies of this element might be present in the genome of X . oryzae pv . oryzae and other xanthomonads.

Appl Environ Microbiol, 2002 Jun, 68(6), 3126 - 8
Characterization of cholylglycine hydrolase from a bile-adapted strain of Xanthomonas maltophilia and its application for quantitative hydrolysis of conjugated bile salts; Dean M et al.; Purified bile salt hydrolase from bile-adapted Xanthomonas maltophilia displays Michaelis-Menten kinetics on cholylglycine and cholyltaurine and hydrolyzes bile salts also in crude bovine bile . The protein is a dimer and is resistant to proteinases and to heating at 55 to 60 degrees C for up to 60 min, in agreement with calorimetric data.

Mol Plant Microbe Interact, 2002 May, 15(5), 463 - 71
rpfF mutants of Xanthomonas oryzae pv . oryzae are deficient for virulence and growth under low iron conditions; Chatterjee S et al.; Xanthomonas oryzae pv . oryzae causes bacterial leaf blight, a serious disease of rice . In the related bacterium Xanthomonas campestris pv . campestris, the rpfF gene is involved in production of a diffusible extracellular factor (DSF) that positively regulates synthesis of virulence-associated functions like extracellular polysaccharide (EPS) and extracellular enzymes . Transposon insertions in the rpfF homolog of X . oryzae pv . oryzae are deficient for virulence and production of a DSF but are proficient for EPS and extracellular enzyme production . The rpfF X . oryzae pv . oryzae mutants exhibit an unusual tetracycline susceptibility phenotype in which exogenous iron supplementation is required for phenotypic expression of a tetracycline resistance determinant that is encoded on an introduced plasmid . The rpfF X . oryzae pv . oryzae mutants also overproduce one or more siderophores and exhibit a growth deficiency under low iron conditions as well as in the presence of reducing agents that are expected to promote the conversion of Fe+3 to Fe+2 . Exogenous iron supplementation promotes migration of rpfF X . oryzae pv . oryzae mutants in rice leaves . The results suggest that rpfF may be involved in controlling an iron-uptake system of X . oryzae pv . oryzae and that an inability to cope with the conditions of low iron availability in the host may be the reason for the virulence deficiency of the rpfF X . oryzae pv . oryzae mutants.

Can J Microbiol, 2002 Apr, 48(4), 342 - 8
Purification and characterization of an alkaline serine endopeptidase from a feather-degrading Xanthomonas maltophilia strain; De Toni CH et al.; A keratinolytic Xanthomonas maltophilia strain (POA-1), cultured on feather meal broth, using keratin as its sole source of carbon and nitrogen, secretes several extracellular peptidases . The major serine peptidase was purified to homogeneity by a five-step procedure . Its purity was evaluated by capillary zone electrophoresis . This enzyme has a molecular mass of 36 kDa, an optimum pH of 9.0, and an optimum temperature of 60 degrees C . The inhibitory profile using protease inhibitors shows that this enzyme is a serine endopeptidase . Besides keratin, the enzyme is active upon the substrates azokeratin, azocasein, and the following fluorogenic peptide substrates: Abz-Leu-Gly-Met-Ile-Ser-Leu-Met-Lys-Arg-Pro-Gln-EDDnp, Abz-Lys-Leu-Cys(SBzl)-Gly-Pro-Lys-Gln-EDDnp, and Abz-Lys-Pro-Cys(SBzl)-Phe-Ser-Lys-Gln-EDDnp.

Eur J Biochem, 2002 May, 269(10), 2464 - 72
Osmoregulated periplasmic glucans of the free-living photosynthetic bacterium Rhodobacter sphaeroides; Talaga P et al.; The osmoregulated periplasmic glucans (OPGs) produced by Rhodobacter sphaeroides, a free-living organism, were isolated by trichloracetic acid treatment and gel permeation chromatography . Compounds obtained were characterized by compositional analysis, matrix-assisted laser desorption ionization mass spectrometry and nuclear magnetic resonance . R . sphaeroides predominantly synthesizes a cyclic glucan containing 18 glucose residues that can be substituted by one to seven succinyl esters residues at the C6 position of some of the glucose residues, and by one or two acetyl residues . The glucans were subjected to a mild alkaline treatment in order to remove the succinyl and acetyl substituents, analyzed by MALDI mass spectrometry and purified by high-performance anion-exchange chromatography . Methylation analysis revealed that this glucan is linked by 17 1,2 glycosidic bonds and one 1,6 glycosidic bond . Homonuclear and (1)H/(13)C heteronuclear NMR experiments revealed the presence of a single alpha-1,6 glycosidic linkage, whereas all other glucose residues are beta-1,2 linked . The different anomeric proton signals allowed a complete sequence-specific assignment of the glucan . The structural characteristics of this glucan are very similar to the previously described OPGs of Ralstonia solanacearum and Xanthomonas campestris, except for its different size and the presence of substituents . Therefore, similar OPGs are synthesized by phytopathogenic as well as free-living bacteria, suggesting these compounds are intrinsic components of the Gram-negative bacterial envelope.

Nature, 2002 May 23, 417(6887), 459 - 63
Comparison of the genomes of two Xanthomonas pathogens with differing host specificities; da Silva AC et al.; The genus Xanthomonas is a diverse and economically important group of bacterial phytopathogens, belonging to the gamma-subdivision of the Proteobacteria . Xanthomonas axonopodis pv . citri (Xac) causes citrus canker, which affects most commercial citrus cultivars, resulting in significant losses worldwide . Symptoms include canker lesions, leading to abscission of fruit and leaves and general tree decline . Xanthomonas campestris pv . campestris (Xcc) causes black rot, which affects crucifers such as Brassica and Arabidopsis . Symptoms include marginal leaf chlorosis and darkening of vascular tissue, accompanied by extensive wilting and necrosis . Xanthomonas campestris pv . campestris is grown commercially to produce the exopolysaccharide xanthan gum, which is used as a viscosifying and stabilizing agent in many industries . Here we report and compare the complete genome sequences of Xac and Xcc . Their distinct disease phenotypes and host ranges belie a high degree of similarity at the genomic level . More than 80% of genes are shared, and gene order is conserved along most of their respective chromosomes . We identified several groups of strain-specific genes, and on the basis of these groups we propose mechanisms that may explain the differing host specificities and pathogenic processes.

J Protein Chem, 2002 Mar, 21(3), 161 - 8
Structural and functional characterization of basic PLA2 isolated from Crotalus durissus terrificus venom; Oliveira DG et al.; The venom of Crotalus durissus terrificus was fractionated by reverse-phase HPLC to obtain crotapotins (F5 and F7) and PLA2 (F15, F16, and F17) of high purity . The phospholipases A2 (PLA2S) and crotapotins showed antimicrobial activity against Xanthomonas axonopodis pv . passiflorae, although the unseparated crotoxin did not . The F17 of the PLA2 also revealed significant anticoagulant activity, althrough for this to occur the presence of Glu 53 and Trp 61 is important . The F17 of the PLA2 showed allosteric behavior in the presence of a synthetic substrate . The amino acid sequence of this PLA2 isoform, determined by automatic sequencing, was HLLQFNKMLKFETRK NAVPFYAFGCYCGWGGQRRPKDATDRCCFVHDCCYEKVTKCNTKWDFYRYSLKSGY ITCGKGTWCKEQICECDRVAAECLRRSLSTYKNEYMFYPDSRCREPSETC . Analysis showed that the sequence of this PLA2 isoform differed slightly from the amino acid sequence of the basic crotoxin subunit reported in the literature . The homology with other crotalid PLA2 cited in the literature varied from 60% to 90% . The pL was estimated to be 8.15, and the calculated molecular weight was 14664.14 as determined by Tricine SDS-PAGE, two-dimensional electrophoresis, and MALDI-TOFF . These results also suggested that the enzymatic activity plays an important role in the bactericidal effect of the F17 PLA2 as well as that of anticoagulation, although other regions of the molecule may also be involved in this biological activity.

Genetika, 2002 Apr, 38(4), 568 - 70
{Synthesis of signaling N-acyl-homoserine-lactones participating in quorum sensing in rhizosphere and soil bacteria Pseudomonas and Xanthomonas}; Khmel' IA et al.; Signaling molecules assigned to N-acyl-homoserine-lactones (AHL) serve as autoinducers for the genes controlling the quorum sensing regulatory system . In many gram-negative bacteria, AHL are the key factors responsible for density-dependent regulation of exoenzyme and secondary metabolite production; they also participate in interaction between bacteria and higher organisms . The soil and rhisosphere bacteria Pseudomonas and Xanthomonas from different geographical zones of Russia and the former USSR were analyzed for the presence of the AHL producers . Screening was conducted by using a test system based on the mutant strain Chromobacterium violaceum, which was unable to synthesize AHL but produced a pigment violacein in the presence of exogenous AHL . The AHL-like compounds proved to be formed by 9.7% of the studied bacteria . Various Pseudomonas species differed in the capacity to synthesize this compounds . In at least a half of the isolated P . aureofaciens and P . aeruginosa, an intense AHL production was observed, whereas the AHL-producers were far less frequent among the P . fluorescens, P . chlororaphis, P . lemonnieri, P . geniculata, and P . putida . None of the 41 Xanthomonas maltophilia strains examined synthesized AHL.

J Chromatogr B Analyt Technol Biomed Life Sci, 2002 Apr 25, 770(1-2), 275 - 81
Identification of xanthans isolated from sugarcane juices obtained from scalded plants infected by Xanthomonas albilineans; Fontaniella B et al.; The exudate gum produced by Xanthomonas albilineans, a specific sugarcane pathogen, has been isolated from juices of diseased sugarcane stalks, hydrolyzed with hydrochloric acid, and the hydrolysate analyzed by capillary electrophoresis . Sucrose . cellobiose, mannose, glucose, glucose-1-P and glucuronic acid were identified as the major components of the polysaccharide isolated from diseased stalks . Juices from healthy stalks contained maltose instead of cellobiose . The chemical nature of this polysaccharide is discussed.

FEMS Microbiol Lett, 2002 Apr 9, 209(2), 149 - 54
Genetic organization of the lexA, recA and recX genes in Xanthomonas campestris; Yang YC et al.; A gene cluster containing lexA, recA and recX genes was previously identified and characterized in Xanthomonas campestris pathovar citri (X . c . pv . citri) . We have now cloned and sequenced the corresponding regions in the Xanthomonas campestris pv . campestris (X . c . pv . campestris) and Xanthomonas oryzae pathovar oryzae (X . o . pv . oryzae) chromosome . Sequence analysis of these gene clusters showed significant homology to the previously reported lexA, recA and recX genes . The genetic linkage and the deduced amino acid sequences of these genes displayed very high identity in different pathovars of X . campestris as well as in X . oryzae . Immunoblot analysis revealed that the over-expressed LexA protein of X . c . pv . citri functioned as a repressor of recA expression in X . c . pv . campestris, indicating that the recombinant X . c . pv . citri LexA protein was functional in a different X . campestris pathovar . The abundance of RecA protein was markedly increased upon exposure of X . c . pv . campestris to mitomycin C, and an upstream region of this gene was shown to confer sensitivity to positive regulation by mitomycin C on a luciferase reporter gene construct . A symmetrical sequence of TTAGTAGTAATACTACTAA present within all three Xanthomonas lexA promoters and a highly conserved sequence of TTAGCCCCATACCGAA present in the three regulatory regions of recA indicate that the SOS box of Xanthomonas strains might differ from that of Escherichia coli.

Mol Microbiol, 2002 May, 44(3), 793 - 802
The repressor for an organic peroxide-inducible operon is uniquely regulated at multiple levels; Mongkolsuk S et al.; ohrR encodes a novel organic peroxide-inducible transcription repressor, and we have demonstrated that ohrR is regulated at the transcriptional and the post-transcriptional levels . Primer extension results show that ohrR transcription initiates at the A residue of the ATG translation initiation codon for the ohrR coding sequence . Thus, the gene has a leaderless mRNA . The ohrR promoter (P1) has high homology to the consensus sequence for Xanthomonas promoters, which is reflected in the high in vivo promoter activity of P1 . Deletion of a 139 bp fragment containing the P1 promoter showed that the sequences upstream of -35 regions were required for neither the promoter activity nor OhrR autoregulation . In vitro, purified OhrR specifically binds to the P1 promoter . DNase I footprinting of OhrR binding to the P1 revealed a 44 bp region of protection on both DNA strands . The protected regions include the -35 and -10 regions of P1 . We suggest that OhrR represses gene expression by blocking RNA polymerase binding to the promoter . There are two steps in the post-transcriptional regulation of ohrR, namely differential stability and inefficient translation of the mRNA . The bicistronic ohrR-ohr mRNA was highly labile and underwent rapid processing in vivo to give only stable monocistronic ohr mRNA and undetectable ohrR mRNA . Furthermore, the ohrR mRNA was inefficiently translated . We propose that, in uninduced cells, the concentration of OhrR is maintained at low levels by the autoregulation mechanism at the transcriptional levels and by the ohrR mRNA instability coupled with inefficient translation at the post-transcriptional level . Upon exposure to an organic peroxide, the compound probably interacts with OhrR and prevents it from repressing the P1 promoter, thus allowing high-level expression of the ohrR-ohr operon . The rapid processing of bicistronic mRNA gives highly stable ohr mRNA and corresponding high levels of Ohr, which remove an organic per-oxide . Once the peroxide has been removed, the autoregulation mechanism feeds back to inhibit the expression of the operon.

Proteomics, 2001 Sep, 1(9), 1111 - 8
Differentially expressed proteins in the interaction of Xanthomonas axonopodis pv . citri with leaf extract of the host plant; Mehta A et al.; The present study reports the expression of proteins of Xanthomonas axonopodis pv . citri in response to different growth conditions . The bacterium was cultured in the basal medium MM1 and in the presence of leaf extracts from a susceptible host plant (sweet orange) as well as a resistant (ponkan) and a nonhost plant (passion fruit) . The protein profiles were analyzed by two-dimensional gel electrophoresis (2-DE) . Twelve differential spots (induced, up- and down-regulated and repressed) were observed in the protein profiles of the bacterium cultivated in citrus extract (susceptible host) when compared to that of MM1 . The 2-DE profile of the bacterium cultured in the complex medium nutrient yeast glycerol was also obtained and the comparison with that of MM1 revealed 36 differential spots . Five proteins from the different treatments were successfully N-terminally sequenced and the putative functions were assigned by homology searches in databases . Two constitutively expressed proteins, B4 and B5, were identified as pseudouridine synthase and elongation factor P, respectively . The large subunit of ribulose 1,5-biphosphate carboxylase/oxygenase and a sulfate binding protein were found as specifically up-regulated in the presence of citrus extracts . Finally, the heat shock protein G was found exclusively in the complex medium and repressed in all other media.

Mol Microbiol, 2002 Jan, 43(2), 371 - 82
A fadD mutant of Sinorhizobium meliloti shows multicellular swarming migration and is impaired in nodulation efficiency on alfalfa roots; Soto MJ et al.; Swarming is a form of bacterial translocation that involves cell differentiation and is characterized by a rapid and co-ordinated population migration across solid surfaces . We have isolated a Tn5 mutant of Sinorhizobium meliloti GR4 showing conditional swarming . Swarm cells from the mutant strain QS77 induced on semi-solid minimal medium in response to different signals are hyperflagellated and about twice as long as wild-type cells . Genetic and physiological characterization of the mutant strain indicates that QS77 is altered in a gene encoding a homologue of the FadD protein (long-chain fatty acyl-CoA ligase) of several microorganisms . Interestingly and similar to a less virulent Xanthomonas campestris fadD(rpfB) mutant, QS77 is impaired in establishing an association with its host plant . In trans expression of multicopy fadD restored growth on oleate, control of motility and the symbiotic phenotype of QS77, as well as acyl-CoA synthetase activity of an Escherichia coli fadD mutant . The S . meliloti QS77 strain shows a reduction in nod gene expression as well as a differential regulation of motility genes in response to environmental conditions . These data suggest that, in S . meliloti, fatty acid derivatives may act as intracellular signals controlling motility and symbiotic performance through gene expression.

J Biochem (Tokyo), 2002 May, 131(5), 757 - 65
A CLN2-related and thermostable serine-carboxyl proteinase, kumamolysin: cloning, expression, and identification of catalytic serine residue; Oyama H et al.; The gene encoding kumamolysin, a thermostable pepstatin-insensitive carboxyl proteinase, was cloned and expressed . (i) Kumamolysin was synthesized as a large precursor consisting of two regions: amino-terminal prepro (188 amino acids) and mature proteins (384 amino acids) . (ii) The deduced amino acid sequence of the mature region exhibited high similarity to those of such bacterial pepstatin-insensitive enzymes as Pseudomonas carboxyl proteinase (PSCP; EC 3.4.23.37, identity = 37%), Xanthomonas carboxyl proteinase (XCP; EC 3.4.23.33, identity = 36%), and human CLN2 gene product (identity = 36%), which is related to a fatal neurodegenerative disease . (iii) The presumed catalytic triad, Glu78, Asp82, Ser278 {three-dimensional structure of PSCP: Wlodawer, A . et al . (2001) Nature Struct . Biol., 8, 442-446}, was found to be conserved in the amino acid sequence of kumamolysin . (iv) Kumamolysin was inactivated by such aldehyde-type inhibitors as Ac-Ile-Pro-Phe-CHO (K(i) = 0.7 0.14 microM) . In PSCP, it has been clarified that these inhibitors form a hemiacetal linkage with the catalytic serine residue and inactivate the enzyme . (v) Mutational analysis of the Ser278 residue revealed that the mutant lost both auto-processing activity and proteolytic activity . These results strongly suggest that kumamolysin has a unique catalytic triad consisting of Glu78, Asp82, and Ser278 residues, as previously observed for PSCP.

Mol Microbiol, 2002 Apr, 44(2), 393 - 401
Involvement of caspase-3-like protein in rapid cell death of Xanthomonas; Gautam S et al.; Xanthomonas campestris pv . glycines strain AM2 (XcgAM2), the aetiological agent of bacterial pustule disease of soybean, as well as some other strains of Xanthomonas including X . campestris pv . malvacearum NCIM 2310 and X . campestris NCIM 2961, exhibited post-exponential rapid cell death (RCD) in Luria-Bertani (LB) medium . RCD was not displayed by Xanthomonas strains while growing in starch medium . Addition of starch to LB culture of XcgAM2 at any point of incubation during the exponential growth was found to arrest the onset of RCD . RCD in this organism was found to be associated with the synthesis of an endogenous enzyme similar to human caspase-3, a known marker of apoptosis in eukaryotes . On sodium dodecyl sulphate polyacrylamide gel elecrophoresis (SDS-PAGE) the XcgAM2 caspase appeared to run along a 55 kDa protein molecular weight marker . The caspase-3-like protein was detected in all Xanthomonas strains tested . RCD was not detected in Escherichia coli cultures in LB medium . The caspase-3-like enzyme activity or pro-tein was also found to be absent in this bacterium . Caspase-3-like protein or Xanthomonas caspase was detected only in the cells of XcgAM2 growing in LB medium and not in those growing in starch medium . The Xanthomonas caspase protein appeared in cells at around 4 h of incubation, and peaked at around 24 h, before finally disappearing at around 54 h of incubation . However, caspase enzyme activity was detected only 12-13 h after incubation and peaked around 18-20 h . Addition of starch at the beginning or during the period of exponential growth in LB cultures of XcgAM2 terminated the synthesis of this protein . It is presumed that starch acted as the repressor of biosynthesis of the Xanthomonas caspase, thereby preventing the organism from undergoing RCD . The cells undergoing RCD also displayed the other markers of eukaryotic apoptosis . These included binding of annexin V to plasma membrane of cells undergoing RCD and the presence of nicked DNA in culture supernatant as evidenced by the TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labelling) assay . Caspase-negative mutants of XcgAM2 did not display post-exponential RCD . The importance of RCD in Xanthomonas life cycle is not yet clear, however the phenomenon appears to have similarities with eukaryotic apoptosis.

Mol Microbiol, 2002 Apr, 44(1), 37 - 48
The Xanthomonas oryzae pv . lozengeoryzae raxP and raxQ genes encode an ATP sulphurylase and adenosine-5'-phosphosulphate kinase that are required for AvrXa21 avirulence activity; Shen Y et al.; Xanthomonas oryzae pv . oryzae (Xoo) Philippine race 6 (PR6) is unable to cause bacterial blight disease on rice lines containing the rice resistance gene Xa21 but is virulent on non-Xa21 rice lines, indicating that PR6 carries avirulence (avrXa21) determinants required for recognition by XA21 . Here we show that two Xoo genes, raxP and raxQ, are required for AvrXa21 activity . raxP and raxQ, which reside in a genomic cluster of sulphur assimilation genes, encode an ATP sulphurylase and APS (adenosine-5'-phosphosulphate) kinase . These enzymes function together to produce activated forms of sulphate, APS and PAPS (3'-phosphoadenosine-5'-phosphosulphate) . Xoo PR6 strains carrying disruptions in either gene, PR6DeltaraxP or PR6DeltaraxQ, are unable to produce APS and PAPS and are virulent on Xa21-containing rice lines . RaxP and RaxQ are similar to the bacterial symbiont Sinorhizobium meliloti host specificity proteins, NodP and NodQ and the Escherichia coli cysteine synthesis proteins CysD, CysN and CysC . The APS and PAPS produced by RaxP and RaxQ are used for both cysteine synthesis and sulphation of other molecules . Mutation in Xoo xcysI, a homologue of Escherichia coli cysI that is required for cysteine synthesis, blocked APS- or PAPS-dependent cysteine synthesis but did not affect AvrXa21 activity, suggesting that AvrXa21 activity is related to sulphation rather than cysteine synthesis . Taken together, these results demonstrate that APS and PAPS production plays a critical role in determining avirulence of a phytopathogen and reveal a commonality between symbiotic and phytopathogenic bacteria.

J Korean Med Sci, 2002 Apr, 17(2), 263 - 5
Two episodes of Stenotrophomonas maltophilia endocarditis of prosthetic mitral valve: report of a case and review of the literature; Kim JH et al.; Stenotrophomonas maltophilia (previously named Xanthomonas maltophilia) is an aerobic, non-fermentive, Gram-negative bacillus that is wide spread in the environment . It was considered to be an organism with limited pathogenic potential, which was rarely capable of causing diseases in human other than those who were in debilitated or immunocompromised state . More recent studies have established that Stenotrophomonas maltophilia can behave as a true pathogen . Endocarditis due to this organism is rare, and only 24 cases of Stenotrophomonas maltophilia endocarditis have been reported in the medical literature . Most cases were associated with risk factors, including intravenous drug abuse, dental treatment, infected intravenous devices, and previous cardiac surgery . We present a case with two episodes of Stenotrophomonas maltophilia endocarditis after mitral valve prosthesis implantation, which was treated with antibiotics initially, and a combination of antibiotics and surgery later . To our knowledge, this is the first case of repetitive endocarditis due to Stenotrophomonas maltophilia.

J Bacteriol, 2002 May, 184(9), 2389 - 98
Functional analysis of HrpF, a putative type III translocon protein from Xanthomonas campestris pv . vesicatoria; Buttner D et al.; Type III secretion systems (TTSSs) are specialized protein transport systems in gram-negative bacteria which target effector proteins into the host cell . The TTSS of the plant pathogen Xanthomonas campestris pv . vesicatoria, encoded by the hrp (hypersensitive reaction and pathogenicity) gene cluster, is essential for the interaction with the plant . One of the secreted proteins is HrpF, which is required for pathogenicity but dispensable for type III secretion of effector proteins in vitro, suggesting a role in translocation . In this study, complementation analyses of an hrpF null mutant strain using various deletion derivatives revealed the functional importance of the C-terminal hydrophobic protein region . Deletion of the N terminus abolished type III secretion of HrpF . Employing the type III effector AvrBs3 as a reporter, we show that the N terminus of HrpF contains a signal for secretion but not a functional translocation signal . Experiments with lipid bilayers revealed a lipid-binding activity of HrpF as well as HrpF-dependent pore formation . These data indicate that HrpF presumably plays a role at the bacterial-plant interface as part of a bacterial translocon which mediates effector protein delivery across the host cell membrane.

Biochem J, 2002 Jul 1, 365(Pt 1), 205 - 11
XpsG, the major pseudopilin in Xanthomonas campestris pv . campestris, forms a pilus-like structure between cytoplasmic and outer membranes; Hu NT et al.; GspG, -H, -I, -J and -K proteins are members of the pseudopilin family . They are the components required for the type II secretion pathway, which translocates proteins across the outer membrane of Gram-negative bacteria to the extracellular milieu . They were predicted to form a pilus-like structure, and this has been shown for PulG of Klebsiella oxytoca by using electron microscopy . In the present study, we performed biochemical analyses of the XpsG protein of Xanthomonas campestris pv . campestris and observed that it is a pillar-like structure spanning the cytoplasmic and outer membranes . Subcellular fractionation revealed a soluble form (SF) of XpsG, in addition to the membrane form . Chromatographic analysis of SF XpsG in the absence of a detergent indicated that it is part of a large complex (>440 kDa) . In vitro studies indicated that XpsG is prone to aggregate in the absence of a detergent . We isolated and characterized a non-functional mutant defective in forming the large complex . It did not interfere with the function of wild-type XpsG and was not detectable in the SF . Moreover, unlike wild-type XpsG, which was distributed in both the cytoplasmic and outer membranes, it appeared only in the cytoplasmic membrane . When wild-type XpsG was co-expressed with His6-tagged XpsH but not with untagged XpsH, SF XpsG bound to nickel and co-eluted with XpsH . This result suggests the presence of other pseudopilin components in the XpsG-containing large-sized molecules.

Int J Syst Evol Microbiol, 2002 Mar, 52(Pt 2), 559 - 68
Stenotrophomonas acidaminiphila sp . nov., a strictly aerobic bacterium isolated from an upflow anaerobic sludge blanket (UASB) reactor; Assih EA et al.; Two of several strictly aerobic, mesophilic bacteria isolated from a lab-scale upflow anaerobic sludge blanket (UASB) reactor treating a petrochemical wastewater, strains AMX 17 and AMX 19T, were subjected to detailed taxonomic study . Cells were gram-negative, motile, non-sporulating, straight to curved rods with a polar flagellum . The isolates exhibited phenotypic traits of members of the genus Stenotrophomonas, including cellular fatty acid composition and the limited range of substrates that could be used . Sugars and many amino acids were utilized . Antibiotic susceptibility and physiological characteristics were determined . The DNA base composition was 66.9 mol% G+C . Phylogenetic analysis revealed that the nearest relatives were Stenotrophomonas maltophilia LMG 11114, Stenotrophomonas nitritireducens DSM 12575T and Pseudomonas pictorum ATCC 23328T (similarity of 98.1-98.8%) . Xanthomonas species, S . maltophilia LMG 958T and Stenotrophomonas africana CIP 104854T showed high 16S rRNA sequence similarities (96.4-97.3%) . The high similarity found in cellular fatty acid profiles and identical partial 16S rRNA sequences (500 bp) for strains AMX 17 and AMX 19T indicate that they belong to the same species . DNA-DNA hybridizations revealed respectively 26.7, 31, 65.8 and 43.6% homology between isolate AMX 19T and S . africana CIP 104854T, S . maltophilia CIP 60.77T, S . nitritireducens DSM 12575T and P . pictorum ATCC 23328T . These results allow the proposal of strain AMX 19T (= DSM 13117T = ATCC 700916T = CIP 106456T) as representative of a novel species of the genus Stenotrophomonas, with the name Stenotrophomonas acidaminiphila sp . nov.

Int J Syst Evol Microbiol, 2002 Mar, 52(Pt 2), 473 - 83
Thermomonas haemolytica gen . nov., sp . nov., a gamma-proteobacterium from kaolin slurry; Busse HJ et al.; Four aerobic, gram-negative bacterial strains isolated from kaolin slurry used in the production of paper were subjected to a polyphasic analysis and characterization to determine their taxonomic position . Analysis of the 16S rDNA sequences of the four strains revealed that they represent a new lineage within the gamma-Proteobacteria, related to the genera Xanthomonas, Pseudoxanthomonas, Stenotrophomonas, Luteimonas, Xylella and Rhodanobacter . Analysis of the quinone system, the polyamines, the fatty acids and the polar lipids revealed a combination of characteristics that is unique and not described for the phylogenetic relatives . The four strains contain a ubiquinone Q-8, spermidine as the major polyamine, diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine as the predominant polar lipids, and a fatty acid profile with predominantly iso-branched fatty acids . The G+C content of the genomic DNA was determined to be within the narrow range 67.1-68.7 mol% . Determination of DNA relatedness, as well as riboprint band patterns and amplified fragment length polymorphism profiles, clearly demonstrated that the four strains are members of a single species . Antibiotic-susceptibility patterns were identical for the four strains . Although showing a high degree of similarites in physiological and biochemical patterns, each of the four strains could be distinguished from the others on the basis of a few biochemical characteristics . On the basis of the estimates of phylogenetic relationships derived from the 16S rDNA sequence analyses, the observed chemotaxonomic characteristics and other phenotypic traits, a new genus, Thermomonas gen . nov., and species, Thermomonas haemolytica sp . nov., are proposed for the strains A50-7-3T (= DSM 13605T = LMG 19653T), B 50-7-1 (= DSM 13598 = LMG 19655), D50-7-1 (= DSM 13610 = LMG 19656) and B50-8-1 (= DSM 13599 = LMG 19654), with strain A50-7-3T as the type strain.

Int J Syst Evol Microbiol, 2002 Mar, 52(Pt 2), 355 - 61
Phylogenetic analysis of Xanthomonas species based upon 16S-23S rDNA intergenic spacer sequences; Goncalves ER et al.; Phylogenetic relationships of 17 species of Xanthomonas were assessed based on analysis of 16S-23S rDNA intergenic spacer (ITS) sequences; a higher level of resolution was obtained than that revealed by 16S rDNA analysis . ITS sequences varied in size from 492 to 578 nt within the genus and the similarity among sequences ranged from 63 to 99% . Major differences were found for the hyacinthi group, which included Xanthomonas albilineans, Xanthomonas hyacinthi, Xanthomonas sacchari, Xanthomonas theicola and Xanthomonas translucens . A common ITS structure with tRNA(Ala) and tRNA(Ile) embedded within the sequence was found for all ITS sequences of Xanthomonas species and for Stenotrophomonas maltophilia . These tRNAs were highly conserved and divided the ITS sequence into three regions (ITS1, ITS2 and ITS3) . ITS1 and ITS2 sequences of Xanthomonas species showed mean similarities of 87.1 and 86.8%, respectively, and differences consisted of substitution and addition/deletion of 1-5 nt . ITS2 showed remarkable variation in sequence length: most species had an ITS2 of 19-20 nt, whereas a long insertion of 51-56 nt was found in Xanthomonas codiaei, X . hyacinthi, Xanthomonas melonis, X . theicola and X . translucens . For ITS3 the most striking alteration was seen in X . hyacinthi, which showed a large deletion of 44 nt . The ITS phylogenetic tree grouped Xanthomonas species into six major clusters . Cluster I included Xanthomonas arboricola, Xanthomonas axonopodis, Xanthomonas bromi, Xanthomonas campestris, X . campestris pv . gardneri, Xanthomonas cassavae, X . codiaei, Xanthomonas cucurbitae, Xanthomonas fragariae, Xanthomonas hortorum, X . melonis, Xanthomonas oryzae, Xanthomonas pisi, Xanthomonas vasicola and Xanthomonas vesicatoria . The species X . albilineans, X . sacchari, X . hyacinthi, X . theicola and X . translucens represented distinct clusters (II-VI) . Topology of the 16S-23S rDNA ITS phylogenetic tree was very similar to that of the 16S rDNA tree reported previously, but more clusters were discriminated because of the higher level of diversity among the ITS sequences (16.2%) compared with the 16S rDNA sequences (1.8%).

Yi Chuan Xue Bao, 2002 Feb, 29(2), 138 - 43
{Identification of a resistance gene to bacterial blight (Xanthomonas oryzae pv . oryzae) in a somaclonal mutant HX-3 of indica rice}; Gao DY et al.; Using the mature embryo of a susceptible rice variety Minghui 63 as the explant, we have obtained a somaclonal mutant HX-3 through selection in vitro, which has showed resistance to bacterial blight . In 8 successive years, the resistance of R1 to R9 generations of HX-3 was identified by ZJ173, a typical bacterial blight strain in Yangtsu River valley, and the results showed that the resistance of HX-3 was stable and heritable . Genetic analysis also indicated that the resistance of HX-3 to bacterial blight was under a dominant gene controlling . Using 32 bacterial blight strains collected in China, Philippines and Japan, the resistance spectrum of HX-3 and other 13 testers with different major dominant resistance genes were tested . Results of 2 years (1999-2000) experiment showed that HX-3 had a broad resistance spectrum, which seemed to be different with those of the other dominant resistance genes identified . Allelic tests were also conducted by crossing HX-3 with IRBB4, IRBB7, CBB12 and IRBB21, and the F2 populations of each of the 4 crosses demonstrated resistant and susceptible plant segregation, indicating that the resistance gene in HX-3 different from Xa-4, Xa-7, Xa-12 and Xa-21 . All these results proved that there was a new resistance gene in HX-3 . We have designated the new gene as Xa-25(t).

Indian J Exp Biol, 2001 Oct, 39(10), 1062 - 4
Effect of phenol on lipid and fatty acid profile of Xanthomonas oryzae pv . oryzae; Mohan N et al.; Effect of phenol on total lipid and fatty acid composition of Xanthomonas oryzae pv . oryzae, the causal agent of bacterial blight of rice (Oryzae sativa) was studied . Lipid level was low in phenol treated cells . Number of fatty acids detected from phenol treated cells was more than those found in untreated cells as revealed by Gas chromatography . Pentadecanoic acid (C15:0), linolenic acid (C18:3) and behenic acid (C22:0) were present only in the treated cells . Palmitic acid which is usually found in bacteria was not detected both in control and treated cells.

Indian J Exp Biol, 2001 Oct, 39(10), 1055 - 61
Effect of phenol on protein and amino acid content of Xanthomonas oryzae pv . oryzae; Mohan N et al.; Leaf blight disease of rice (Oryza sativa) is caused by the bacterium Xanthomonas oryzae pv . oryzae . Phenol (1 to 4 mM) induced changes in protein profiles of X . o . pv . oryzae and a stress protein with a molecular mass of 69,000 appeared . HPLC analysis indicated occurrence of amino acids such as asparagine, alanine, methionine and cystine in phenol treated cells . Proton NMR analysis also revealed variation on the presence of amino acids in the cells treated with phenol.

Carbohydr Res, 2002 Mar 1, 337(5), 391 - 6
Synthesis of an xylosylated rhamnose pentasaccharide, the repeating unit of the O-chain polysaccharide of the lipopolysaccharide of Xanthomonas campestris pv . begoniae GSPB 525; Zhang J et al.; A xylosylated rhamnose pentasaccharide, alpha-L-Rhap-(1-->3)-{beta-L-Xylp-(1-->2)-}-alpha-L-Rhap-(1-->3)-{beta-L-Xylp-(1-->4)}-L-Rhap, the repeating unit of the O-chain polysaccharide (OPS) of the lipopolysaccharides of Xanthomonas campestris pv . begoniae GSPB 525 was synthesized by a highly regio- and stereoselective way . Thus coupling of 1,2-O-ethylidene-beta-L-rhamnopyranose (1) with 2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl trichloroacetimidate (2) to give (1-->3)-linked disaccharide (3), subsequent benzoylation, deethylidenation, acetylation, 1-O-deacetylation, and trichloroacetimidation afforded the disaccharide donor 11 . Condensation of 11 with 1 yielded 2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl-(1-->3)-2-O-acetyl-4-O-benzoyl-alpha-L-rhamnopyranosyl-(1-->3)-1,2-O-ethylidene-beta-L-rhamnopyranose (12), and selective deacetylation of 12 yielded the trisaccharide diol acceptor 15 . Coupling of 15 with 2,3,4-tri-O-benzoyl-alpha-L-xylopyranosyl trichloroacetimidate (16), followed by deprotection, gave the target pentasaccharide 19.

Plant Mol Biol, 2002 Feb 1, 48(3), 243 - 54
Induction of pepper cDNA encoding a lipid transfer protein during the resistance response to tobacco mosaic virus; Park CJ et al.; Pepper (Capsicum annuum) plants exhibit hypersensitive response (HR) against infection by many tobamoviruses . A clone encoding a putative nonspecific lipid transfer protein (CaLTP1) was isolated by differential screening of a cDNA library from resistant pepper leaves when inoculated with tobacco mosaic virus (TMV) pathotype P0 . The predicted amino acid sequence of CaLTP1 is highly similar to that of the other plant LTPs . Southern blot analysis showed that a small gene family of LTP-related sequences was present in the pepper genome . Transcripts homologous to CaLTP1 accumulated abundantly in old leaves and flowers . CaLTP1 expression was induced in the incompatible interaction with TMV-P0 but was not induced in the compatible interaction with TMV-P1.2 . In correlation with the temporal progression of HR in the inoculated leaves, CaLTP1 transcripts started to accumulate at 24 h after TMV-P0 inoculation, reaching a maximal level at 48 h . A strain of Xanthomonas campestris pv . vesicatoria (Xcv) that carries the bacterial avirulence gene, avrBs2, was infiltrated into leaves of a pepper cultivar containing the Bs2 resistance gene . A marked induction of CaLTP1 expression was observed in Xcv-infiltrated leaves . Effects of exogenously applied abiotic elicitors on CaLTP1 expression were also examined . Salicylic acid caused a rapid accumulation of CaLTP1 transcripts in pepper leaves and ethephon treatment also induced the expression of the CaLTP1 gene . Transient expression in the detached pepper leaves by biolistic gene bombardment indicated that CaLTP1 is localized mostly at the plant cell surface, possibly in the cell wall . These results suggest possible role(s) for LTPs in plant defense against pathogens including viruses.

J Appl Microbiol, 2001 Dec, 91(6), 1044 - 50
A 3.1-kb genomic fragment of Bacillus subtilis encodes the protein inhibiting growth of Xanthomonas oryzae pv . oryzae; Lin D et al.; AIMS: To clone genes of Bacillus subtilis encoding peptides that inhibit the growth of Xanthomonas orzae pv . oryzae (Xoo) . METHODS AND RESULTS: A 3.1-kb DNA fragment from B . subtilis SO113 encoding peptides that inhibit the growth of Xoo (anti-Xoo, showing an inhibition zone) was isolated from a plasmid library of B . subtilis 6 GM15 . Sequence analysis revealed that it contained three complete open reading frames (ORFs): ybcO, ybcS and a novel ORF designated ybcPQ . Deleting the last 96 bp of ybcS from the plasmid eliminated the anti-Xoo activity, suggesting that ybcS is required for producing the anti-Xoo activity . However, no anti-Xoo activity could be detected for the plasmid with ybcS alone . Further analysis showed that ybcO, at least, was also required to obtain the anti-Xoo activity . CONCLUSIONS: A fragment of B . subtilis has been cloned that expresses an anti-Xoo activity that requires ybcS and ybcO . SIGNIFICANCE AND IMPACT OF THE STUDY: These genes could be useful for the genetic engineering of resistance to rice bacterial diseases and for the design of new anti-Xoo biocontrol agents.

Plant J, 2002 Feb, 29(4), 487 - 95
Prior exposure to lipopolysaccharide potentiates expression of plant defenses in response to bacteria; Newman MA et al.; Lipopolysaccharide (LPS) is a ubiquitous component of Gram-negative bacteria which has a number of diverse biological effects on eukaryotic cells . In contrast to the large body of work in mammalian and insect cells, the effects of LPS on plant cells have received little attention . LPS can induce defense-related responses in plants, but in many cases these direct effects are weak . Here we have examined the effects of prior inoculation of LPS on the induction of plant defense-related responses by phytopathogenic xanthomonads in leaves of pepper (Capsicum annuum) . The resistance of pepper to incompatible strains of Xanthomonas axonopodis pv . vesicatoria or to X . campestris pv . campestris is associated with increased synthesis of the hydroxycinnamoyl-tyramine conjugates, feruloyl-tyramine (FT) and coumaroyl-tyramine (CT) . FT and CT are produced only in trace amounts in response to compatible strains of X . axonopodis pv . vesicatoria . Treatment of leaves with LPS from a number of bacteria did not induce the synthesis of FT and CT but altered the kinetics of induction upon subsequent bacterial inoculation . In incompatible interactions FT and CT synthesis was accelerated, whereas in compatible interactions synthesis was also considerably enhanced . The ability of the tissue to respond more rapidly was induced within 4 h of LPS treatment and the potentiated state was maintained for at least 38 h . Earlier treatment with LPS also potentiated the expression of other defense responses such as transcription of genes encoding acidic beta-1,3-glucanase . Our findings indicate a wider role for LPS in plant-bacterial interactions beyond its limited activity as a direct inducer of plant defenses.

Biochem Biophys Res Commun, 2002 Feb 22, 291(2), 338 - 43
Mutation in the Xanthomonas campestris xanA gene required for synthesis of xanthan and lipopolysaccharide drastically reduces the efficiency of bacteriophage (phi)L7 adsorption; Hung CH et al.; (Phi)L7 is a lytic phage infecting the gram-negative Xanthomonas campestis pv . campestris, a plant pathogen . To study phage-host interaction, a (phi)L7-resistant mutant was isolated from strain Xc17 by mini-Tn5 transposition and designated CH7LR . CH7LR could not plate (phi)L7 in double-layered assay and formed turbid clearing zones when the cell lawn was dropped with a high titer of (phi)L7 . Sequence analysis showed that the mutated gene is xanA coding for phosphoglucomutase/phosphomannomutase, required for the synthesis of lipopolysaccharide and exopolysaccharide (xanthan) . The involvement of xanA was confirmed by isolating another mutant with interrupted xanA and complementing with the cloned wild-type gene . Nonmucoid mutants are still sensitive to (phi)L7, indicating that xanthan is not involved in (phi)L7 adsorption . Since the mutants still exhibited low efficiencies of phage adsorption, we predict, by analogy with the cases in other bacteriophages of gram-negative bacteria, that other outer membrane components such as a protein are required for the formation of a complex receptor . (c)2002 Elsevier Science (USA).

Carbohydr Res, 2002 Feb 18, 337(4), 315 - 26
Biosynthesis of a substituted cellulose from a mutant strain of Xanthomonas campestris; Vojnov AA et al.; In Xanthomonas campestris the genes involved in polysaccharide (xanthan) biosynthesis are located in a gene cluster (gum) of 16 kb . A Tn5 insertion mutant with a reduced slimy phenotype has been characterized . This mutant failed to produce the pentasaccharide repeating-unit of xanthan . Only three sugars were transferred to the prenyl phosphate intermediate . Several lines of evidence suggested that the lipid-associated saccharide was the trisaccharide reducing end of the pentasaccharide from the wild-type strain . This trisaccharide was built up from UDP-Glc and GDP-Man, and a glucose residue was at the reducing end, linked to an allylic prenol through a diphosphate bridge . Results from one- or two-stage reactions showed that the trisaccharide-P-P-polyprenol was the precursor of the polymer . This new polymer, a polytrisaccharide, was detected also in vivo . The transposon responsible for the mutation was located within gumK gene . Therefore, this gene encodes for the glycosyltransferase IV, which catalyses the transfer of glucuronic acid to the lipid-linked beta-D-Manp-(1-->3)-beta-D-Glcp-(1-->4)-beta-D-Glcp trisaccharide . A recombinant plasmid with the whole gum cluster restored the wild type phenotype.

Appl Environ Microbiol, 2002 Feb, 68(2), 699 - 704
16S ribosomal DNA-based analysis of bacterial diversity in purified water used in pharmaceutical manufacturing processes by PCR and denaturing gradient gel electrophoresis; Kawai M et al.; The bacterial community in partially purified water, which is prepared by ion exchange from tap water and is used in pharmaceutical manufacturing processes, was analyzed by denaturing gradient gel electrophoresis (DGGE) . 16S ribosomal DNA fragments, including V6, -7, and -8 regions, were amplified with universal primers and analyzed by DGGE . The bacterial diversity in purified water determined by PCR-DGGE banding patterns was significantly lower than that of other aquatic environments . The bacterial populations with esterase activity sorted by flow cytometry and isolated on soybean casein digest (SCD) and R2A media were also analyzed by DGGE . The dominant bacterium in purified water possessed esterase activity but could not be detected on SCD or R2A media . DNA sequence analysis of the main bands on the DGGE gel revealed that culturable bacteria on these media were Bradyrhizobium sp., Xanthomonas sp., and Stenotrophomonas sp., while the dominant bacterium was not closely related to previously characterized bacteria . These data suggest the importance of culture-independent methods of quality control for pharmaceutical water.

Mol Genet Genomics, 2001 Dec, 266(4), 639 - 45 Epub 2001 Oct 10.
Chromosome landing at the tomato Bs4 locus; Ballvora A et al.; The tomato (Lycopersicon esculentum) Bs4 gene confers resistance to strains of Xanthomonas campestris pathovar vesicatoria that express the avirulence protein AvrBs4 . As part of a map-based cloning strategy for the isolation of Bs4, we converted Bs4-linked amplified fragment length polymorphism (AFLP) and restriction fragment length polymorphism (RFLP) markers into locus-specific sequence-tagged-site (STS) markers . The use of these markers for the analysis of 1972 meiotic events allowed high-resolution genetic mapping within a 1.2-cM interval containing the target gene . Two tomato yeast artificial chromosome (YAC) clones, each harboring inserts of approximately 250 kb, were identified using the marker most closely linked to Bs4 . YAC end-specific markers were established and employed to construct a local YAC contig . The ratio of physical to genetic distance at Bs4 was calculated to be 280 kb/cM, revealing that recombination rates in this region are about three times higher than the genome-wide average . Mapping of YAC end-derived markers demonstrated that the Bs4 locus maps within a region of 250 kb, corresponding to a genetic interval of 0.9 cM.

J Exp Bot, 2002 Feb, 53(367), 383 - 5
Pathogen-induced expression of cyclo-oxygenase homologue in hot pepper (Capsicum annuum cv . Pukang); Kim YC et al.; The hypersensitive reaction (HR) in plants is typified by a rapid and localized cell death at the site of pathogen infection . To understand better the molecular and cellular defence mechanism controlling HR, hot pepper leaves (Capsicum annuum cv . Pukang) were inoculated with the soybean pustule pathogen Xanthomonas campestris pv . glycine 8ra . By using the DD-PCR technique, a cDNA fragment was identified that exhibited a sequence similarity to the recently identified tobacco pathogen-induced oxygenase (PIOX) with homology to animal cyclo-oxygenase (COX) . Subsequently, the full-length cDNA clone, pCa-COX1, encoding the COX homologue from the pathogen-inoculated hot pepper leaf cDNA library was isolated . The deduced amino acid sequence of Ca-COX1 shares 85.8% identity with tobacco PIOX and displays a significant degree of sequence identity (21.7-23.7%) with mammalian COXs . The expression of Ca-COX1 was markedly induced at 4-12 h after pathogen infection, while HR cell death on pepper leaves appeared at approximately 15 h post-inoculation . These results are consistent with the notion that the lipid-derived signalling pathway is involved in the initial response of hot pepper plants to pathogen infection.

J Bacteriol, 2002 Feb, 184(3), 831 - 9
NolX of Sinorhizobium fredii USDA257, a type III-secreted protein involved in host range determination, Iis localized in the infection threads of cowpea (Vigna unguiculata {L.} Walp) and soybean (Glycine max {L.} Merr.) nodules; Krishnan HB; Sinorhizobium fredii USDA257 forms nitrogen-fixing nodules on soybean (Glycine max {L.} Merr.) in a cultivar-specific manner . This strain forms nodules on primitive soybean cultivars but fails to nodulate agronomically improved North American cultivars . Soybean cultivar specificity is regulated by the nolXWBTUV locus, which encodes part of a type III secretion system (TTSS) . NolX, a soybean cultivar specificity protein, is secreted by TTSS and shows homology to HrpF of the plant pathogen Xanthomonas campestris pv . vesicatoria . It is not known whether NolX functions at the bacterium-plant interface or acts inside the host cell . Antibodies raised against S . fredii USDA257 NolX were used in immunocytochemical studies to investigate the subcellular localization of this protein . Immunostaining of paraffin-embedded sections of developing soybean and cowpea (Vigna unguiculata {L.} Walp) nodules revealed localization of NolX in the infection threads . Protein A-gold immunocytochemical localization studies utilizing affinity-purified NolX antibodies revealed specific deposition of gold particles in the fibrillar material inside infection threads . Similar immunogold localization studies failed to detect NolX in thin sections of mature soybean and cowpea nodules . The results from this study indicate that NolX is expressed in planta only during the early stages of nodule development.

Zhonghua Jie He He Hu Xi Za Zhi, 1999 Apr, 22(4), 211 - 3
{Analysis of clinical characteristics and drug sensitivity tests of lower respiratory tract infection by Xanthomonas maltophilia}; Liu Z et al.; OBJECTIVE: To analyse the clinical characteristics of lower respiratory tract infection caused by Xanthomonas maltophilia and to investigate the antibiotic sensitivity of Xanthomonas maltophilia strains . METHODS: Retrospective study of the clinical data of 54 cases with lower respiratory tract infection by Xanthomonas maltophilia, including risk factors of morbidity, clinical symptoms and signs, X-ray findings, blood routine test, treatment and prognosis . Drug sensitivity against strains of Xanthomonas maltophilia by K-B method was studied . RESULTS: There were 39 males and 15 females, the mean age being 51 +/- 17 years . 87% of the cases had underlying diseases, most of which were COPD complicated by respiratory failure . 57% of the cases were immunocompromised . 39% of the cases were in ICU or CCU . 54% of the cases accepted invasive treatments, and 93% of the cases were given broad-spectrum antibiotics . Clinical manifestations include chill (72%), fever (80%), cough (94%) and expectoration (91%) . The chest X-ray revealed infiltration in lower lobes of both lungs . 16 cases had consolidations, and 11 cases were complicated with pleural effusions . The drug sensitivity test in vitro showed that these strains were multiresistant to commonly used antibiotics, and drugs whose sensitive rate were over 50% included SMZco, ceftazidine, and timentin . CONCLUSIONS: The lower respiratory tract infections caused by Xanthomonas maltophilia develop at patients with various underlying diseases, especially in the immunocompromised patients . Risk factors of morbidity were: patients in ICU or CCU, acceptance of invasive treatment and inappropriate use of broad-spectrum antibiotics . Clinical manifestations include severely toxic symptoms and some cases had pulmonary consolidations and pleural effusions.

Plant Cell Physiol, 2001 Dec, 42(12), 1321 - 30
A pathogen-induced chitin-binding protein gene from pepper: its isolation and differential expression in pepper tissues treated with pathogens, ethephon, methyl jasmonate or wounding; Lee SC et al.; A chitin-binding protein (CBP) cDNA (CACBP1) was isolated from a cDNA library of pepper (Capsicum annuum L.) leaves infected with Xanthomonas campestris pv . vesicatoria . The deduced amino acid sequence of the CACBP1 gene which has chitin-binding domain and hinge region shares a high level of identity with CBP sequences from tomato, potato and tobacco . The CACBP1 gene was organ-specifically regulated in pepper plants, and differentially induced during the compatible and incompatible interactions of pepper with X . campestris pv . vesicatoria or Phytophthora capsici . Expression of the CACBP1 gene was rapidly induced in the incompatible interactions upon pathogen infection . Transcripts of the CACBP1 gene was highly inducible in the leaves of matured pepper plants by Colletotrichum coccodes infection . In situ hybridization results showed that CACBP1 mRNA was expressed in the phloem area of vascular bundles in C . coccodes-infected leaf tissues . The pathogen-inducible CACBP1 gene was also strongly induced and accumulated in pepper leaves by ethephon, methyl jasmonate or wounding . These data suggest that ethylene and jasmonate may act as signal molecules in the signal transduction pathways of the CBP gene induction during the pepper defense- or pathogenesis-related plant responses.

Mol Plant Microbe Interact, 2001 Dec, 14(12), 1411 - 9
Vascular defense responses in rice: peroxidase accumulation in xylem parenchyma cells and xylem wall thickening; Hilaire E et al.; The rice bacterial blight pathogen Xanthomonas oryzae pv . oryzae is a vascular pathogen that elicits a defensive response through interaction with metabolically active rice cells . In leaves of 12-day-old rice seedlings, the exposed pit membrane separating the xylem lumen from the associated parenchyma cells allows contact with bacterial cells . During resistant responses, the xylem secondary walls thicken within 48 h and the pit diameter decreases, effectively reducing the area of pit membrane exposed for access by bacteria . In susceptible interactions and mock-inoculated controls, the xylem walls do not thicken within 48 h . Xylem secondary wall thickening is developmental and, in untreated 65-day-old rice plants, the size of the pit also is reduced . Activity and accumulation of a secreted cationic peroxidase, PO-C1, were previously shown to increase in xylem vessel walls and lumen . Peptide-specific antibodies and immunogold-labeling were used to demonstrate that PO-C1 is produced in the xylem parenchyma and secreted to the xylem lumen and walls . The timing of the accumulation is consistent with vessel secondary wall thickening . The PO-C1 gene is distinct but shares a high level of similarity with previously cloned pathogen-induced peroxidases in rice . PO-C1 gene expression was induced as early as 12 h during resistant interactions and peaked between 18 and 24 h after inoculation . Expression during susceptible interactions was lower than that observed in resistant interactions and was undetectable after infiltration with water, after mechanical wounding, or in mature leaves . These data are consistent with a role for vessel secondary wall thickening and peroxidase PO-C1 accumulation in the defense response in rice to X . oryzae pv . oryzae.

Genome, 2001 Dec, 44(6), 1046 - 56
Mapping genetic factors affecting the reaction to Xanthomonas axonopodis pv . phaseoli in Phaseolus vulgaris L . under field conditions; Tarlan B et al.; The objectives of the present study were to evaluate the field effects of Xanthomonas axonopodis pv . phaseoli (Xap), which causes common bacterial blight (CBB) on common bean (Phaseolus vulgaris L.), and to identify genetic factors for resistance to CBB using a linkage map constructed with random amplified polymorphic DNA (RAPD), restriction fragment length polymorphism (RFLP), simple sequence repeat (SSR), and amplified fragment length polymorphism (AFLP) markers . One hundred and forty-two F2:4 lines, derived from a cross between 'OAC Seaforth' and 'OAC 95-4', and the parents were evaluated for their field reaction to CBB . In the inoculated plots, the reaction to CBB was negatively correlated with seed yield, days to maturity, plant height, hypocotyl diameter, pods per plant, and harvest index . A reduction in seed yield and its components was observed when disease-free and CBB-inoculated plots were compared . The broad-sense heritability estimate of the reaction to CBB was 0.74 . The disease segregation ratio was not significantly different from the expected segregation ratio for a single locus in an F2 generation . The major gene for CBB resistance was localized on linkage group (LG) G5 . A simple interval mapping procedure identified three genomic regions associated with the reaction to CBB . One quantitative trait loci (QTL), each on LG G2 (BNG71Dra1), G3 (BNG21EcoRV), and G5 (PHVPVPK-1) explained 36.3%, 10.2%, and 42.2% of the phenotypic variation for the reaction to CBB, respectively . Together, these loci explained 68.4% of the phenotypic variation . The relative positions of these QTL on the core common bean map and their comparison with the previous QTL for CBB resistance are discussed.

Mol Plant Microbe Interact, 2001 Nov, 14(11), 1335 - 9
Novel genomic locus with atypical G+C content that is required for extracellular polysaccharide production and virulence in Xanthomonas oryzae pv . oryzae; Dharmapuri S et al.; Three exopolysaccharide (EPS)- and virulence-deficient mutants of Xanthomonas oryzae pv . oryzae, the causal agent of bacterial leaf blight of rice, were isolated by Tn5 mutagenesis . These insertions are not located within the gum gene cluster . A 40-kb cosmid clone that restored EPS production and virulence to all three mutants was isolated, and the three transposon insertions were localized to contiguous 4.3- and 3.5-kb EcoRI fragments that are included in this clone . Sequence data indicate that two of the transposon insertions are in genes that encode a putative sugar nucleotide epimerase and a putative glycosyl transferase, respectively; the third insertion is located between the glycosyl transferase gene and a novel open reading frame (ORF) . A 5.5-kb genomic region in which these three ORFs are located has a G+C content of 5-1.7%, quite different from the G+C content of approximately 65.0% that is typical of X . oryzae pv . oryzae . Homologues of this locus have not yet been reported in any other xanthomonad.

Biochem Genet, 2001 Oct, 39(9-10), 289 - 96
Differential esterase expression in leaves of Manihot esculenta Crantz infected with Xanthomonas axonopodis pv . manihotis; Pereira AJ et al.; The polyacrylamide gel electrophoresis system (PAGE) and inhibition tests for biochemical characterization of alpha- and beta-esterases were used to obtain a functional classification of esterases in plants and to show a differential expression of esterases as markers of pathogenesis in cassava plants (Manihot esculenta Crantz) . The characterization of alpha- and beta-esterases from leaves of M . esculenta by the PAGE system was possible using an extraction solution containing two phenol-complexing agents (PVP-40 and sodium metabisulfite), three antioxidant agents (EDTA, beta-mercaptoethanol, and DTT), and one quinone reducer (ascorbic acid) . Fourteen esterase isozymes were detected in young unexpanded leaves of M . esculenta cultivars . The inhibition pattern of alpha- and beta-esterases of M . esculenta showed that Est-9 is an arylesterase, and in the unexpanded leaves of the M . esculenta plants infected with Xanthomonas axonopodis pv . manihotis, the Est-7 beta-esterase showed the characteristic staining of an alpha/beta-esterase . This diffrential expression of Est-7 isozyme in young unexpanded leaves of cassava plants can be used as a marker of pathogenesis after infection with X . axonopodis pv . manihotis.

Arch Microbiol, 2001 Dec, 176(6), 415 - 20 Epub 2001 Sep 12.
Regulation of the synthesis of cyclic glucan in Xanthomonas campestris by a diffusible signal molecule; Vojnov AA et al.; The rpf gene cluster of Xanthomonas campestris pv . campestris is involved in the co-ordinate positive regulation of the production of extracellular enzymes and the extracellular polysaccharide xanthan . Several of the rpf genes are involved in a regulatory system involving the small diffusible molecule DSF (for diffusible signal factor) . Synthesis of DSF requires RpfF, and a two-component sensory transduction system involving RpfC has been implicated in the perception of the signal and signal transduction . Here we show that mutations in both rpfF and rpfC lead to reductions in the levels of cyclic glucan . The levels of cyclic glucan synthetase in membrane preparations from rpfF and rpfC mutants were, however, unaltered from the wild-type . Similar alterations in the level of cyclic glucan without changes in cyclic glucan synthetase activity were seen when wild-type bacteria were exposed to osmotic stress . These results extend the range of cellular functions subject to regulation by the rpf genes and DSF system.

FEMS Microbiol Lett, 2001 Nov 27, 205(1), 83 - 9
Characterization of Xanthomonas oryzae pv . oryzae recX, a gene that is required for high-level expression of recA; Sukchawalit R et al.; Analysis of the nucleotide sequence downstream from the Xanthomonas oryzae pv . oryzae recA gene reveals two orfs designated orfX and recX . The former has the potential to code for a 5.6 kDa protein of unknown function while the latter encodes for a putative 14.6 kDa protein with homology to RecX from various bacteria . Northern blot analysis and RT-PCR results show that recA-orfX-recX are co-regulated and arranged in an operon . A recX mutant was constructed . The mutant has no obvious growth defects or stress response defects, except that it cannot support high-level expression of recA from an expression vector . Introduction of the plasmid containing recA into the recX mutant resulted in reduced transformation efficiency and all transformants tested had mutations with reduced RecA levels . Moreover, the recX mutant has reduced basal levels of RecA . This has not been observed in other bacteria . When inactivated recX was complemented in trans, both changes were reversed . recX mutation has no effect on the regulation of the recA promoter, suggesting that its effect on the RecA level could be post-transcriptional.

Steroids, 2002 Jan, 67(1), 51 - 6
7alpha-OH epimerisation of bile acids via oxido-reduction with Xanthomonas maltophilia; Medici A et al.; The microbial 7alpha-OH epimerisation of cholic, chenodeoxycholic, and 12-ketochenodeoxycholic acids (7alpha-OH bile acids) with Xanthomonas maltophilia CBS 827.97 to corresponding 7beta-OH derivatives with scarcity of oxygen is described . With normal pressure of oxygen the 7-OH oxidation products are obtained . No biotransformations are achieved in anaerobic conditions . The microbial 7alpha-OH epimerisation is achieved by oxidation of 7-OH function and subsequent reduction . Partial purification, in fact, of the enzymatic fraction revealed the presence of two hydroxysteroid dehydrogenases (HSDH) alpha- and beta-stereospecific together with a glycocholate hydrolase . On the basis of these results a further application is the microbial reduction of 6alpha-fluoro and 6beta-fluoro-3alpha-hydroxy-7-oxo-5beta-cholan-24-oic acid methyl esters to the corresponding 7alpha-OH and 7beta-OH derivatives.

Mol Genet Genomics, 2001 Nov, 266(3), 425 - 35
Plasmids carrying cloned fragments of RF DNA from the filamentous phage (phi)Lf can be integrated into the host chromosome via site-specific integration and homologous recombination; Lin NT et al.; Different regions of RF DNA from the filamentous bacteriophage phiLf were cloned in Escherichia coli vectors that can not be maintained in Xanthomonas . After introduction into X . campestris pv . campestris 17 (Xc17), most of these constructs were found to integrate into the host chromosome, either by recA-dependent homologous recombination or recA-independent site-specific integration . Mutations in himA, which codes for the alpha-subunit of the Integration Host Factor, does not affect the integration . Integration occurs into a chromosomal region which harbors a copy of a defective phage (4445 bp) that shares a high degree of identity with the phiLf genome . While various parts of the 4445-bp region are susceptible to homologous recombination, site-specific integration requires the attB sequence on the chromosome and the phage attP . The attB shows a high level of sequence identity (22 out of 28 bp) to the dif site required for E . coli Xer site-specific recombination, including the 6-bp central region, and 8/11 identity in both the left XerC-binding arm and the right XerD-binding arm, with the innermost 5 nt of the arms forming a dyad symmetry that is also present in dif . The attP has the same central region and shows 10/11 identity to the dif site in the left arm, but the sequence of the right arm is less conserved than that of attB . The smallest regions still capable of mediating integration are a cloned 72-bp phiLf attP-containing sequence and a 51-bp Xc17 attB-containing sequence, which was reinserted into the Xc17 chromosome after the 4445-bp region had been deleted, indicating that accessory sequences are not necessary and that the integrase required for site-specific integration is neither specified by the 4445-bp Xc17 chromosomal region nor encoded by the phiLf genome.

Mol Cells, 2001 Oct 31, 12(2), 250 - 6
Induction of a pepper cDNA encoding SAR8.2 protein during the resistance response to tobacco mosaic virus; Lee GJ et al.; A cDNA library was constructed with mRNA extracted from TMV resistant hot pepper plants 24 and 48 h after inoculation by TMV . The library was screened differentially with radio-labeled cDNA synthesized with mRNA from the leaves of either TMV-inoculated or mock-inoculated hot pepper plants . CaSAR8.2 clone was one of the clones isolated by this differential screening . The predicted amino acid sequence of CaSAR8.2 has a homology of 52% similarity to that of tobacco SAR8.2 genes . Southern blot analysis showed that a multigene family of CaSAR8.2 was present in the hot pepper genome . Transcripts homologous to CaSAR8.2 accumulated abundantly in the leaves and the flowers, but little in other tissues . CaSAR8.2 gene expression was induced by avirulent pathotype TMV-P0 inoculation but not by virulent TMV-P1.2 inoculation . Effects of exogenously applied abiotic elicitors on CaSAR8.2 expression were also examined . Salicylic acid and ethephon treatments caused a rapid accumulation of CaSAR8.2 transcripts in pepper leaves and methyl jasmonate treatment slightly induced the expression of CaSAR8.2 . A strain of Xanthomonas campestris pv . vesicatoria (Xcv) that contains an avirulence gene avrBs2, was infiltrated into the leaves of a pepper cultivar containing the Bs2 resistance gene . A marked induction of CaSAR8.2 gene expression was observed in Xcv-infiltrated leaves . These results suggest possible roles of CaSAR8.2 as pathogenesis-related protein against varieties of pathogens including virus and bacteria.

FEMS Microbiol Lett, 2001 Oct 16, 204(1), 175 - 81
Dimethoxyphenol oxidase activity of different microbial blue multicopper proteins; Solano F et al.; 2,6-Dimethoxyphenol is a versatile substrate for Pyricularia oryzae laccase, PpoA from Marinomonas mediterranea, phenoxazinone synthase from Streptomyces antibioticus and mammalian ceruloplasmin . In addition, in cellular extracts of microorganisms expressing other blue multicopper proteins with no enzymatic activity previously described, such as Escherichia coli (copper resistance CueO), Pseudomonas syringae and Xanthomonas campestris (copper resistance CopA), Bacillus subtilis (sporulation protein CotA) and Saccharomyces cerevisiae (iron transporter Fet3p), laccase activity is detected under appropriate conditions . This oxidase activity can be spectrophotometrically followed by the oxidation of 2,6-dimethoxyphenol . Specific staining after SDS-PAGE is also possible for some of these proteins . This detection assay can facilitate the study of the multiple functions that such proteins seem to carry out in a variety of microorganisms.

Genetics, 2001 Oct, 159(2), 757 - 65
Are the dominant and recessive plant disease resistance genes similar? A case study of rice R genes and Xanthomonas oryzae pv . oryzae races; Li ZK et al.; The resistance of rice to its bacterial blight pathogen Xanthomonas oryzae pv . oryzae (Xoo) has both qualitative and quantitative components that were investigated using three near-isogenic line sets for four resistance (R) genes (Xa4, xa5, xa13, and Xa21) and 12 Xoo races . Our results indicate that these two resistance components of rice plants were associated with the properties of the R genes . The qualitative component of the R genes was reflected by their large effects against corresponding avirulent Xoo races . The quantitative component of the R genes was their residual effects against corresponding virulent races and their epistatic effects, which together could lead to high-level resistance in a race-specific manner . Our results revealed important differences between the different types of R genes . Two R genes, Xa4 and Xa21, showed complete dominance against the avirulent Xoo races and had large residual effects against virulent ones . They acted independently and cumulatively, suggesting they are involved in different pathways of the rice defensive system . The third R gene, xa5, showed partial dominance or additivity to the avirulent Xoo races and had relatively small but significant residual effects against the virulent races . In contrast, xa13 was completely recessive, had no residual effects against the virulent races, and showed more pronounced race specificity . There was a strong interaction leading to increased resistance between xa13 and xa5 and between either of them and Xa4 or Xa21, suggesting their regulatory roles in the rice defensive pathway(s) . Our results indicated that high-level and durable resistance to Xoo should be more efficiently achieved by pyramiding different types of R genes.

Biochem Genet, 2001 Aug, 39(7-8), 261 - 78
Marker assisted selection of bacterial blight resistance genes in rice; Davierwala AP et al.; Bacterial leaf blight caused by Xanthomonas oryzae pv . oryzae is one of the most important diseases affecting rice production in Asia . We were interested in surveying rice genotypes that are popularly used in the Indian breeding program for conferring resistance to bacterial blight, using 11 STMS and 6 STS markers . The basis of selection of these DNA markers was their close linkage to xa5, xa13, and Xa21 genes and their positions on the rice genetic map relative to bacterial blight resistance genes . Eight lines were found to contain the xa5 gene while two lines contained Xa21 gene and none of the lines contained the xa13 gene with the exception of its near-isogenic line . Using the polymorphic markers obtained in the initial survey, marker-assisted selection was performed in the F3 population of a cross between IR-64 and IET-14444 to detect lines containing multiple resistance genes . Of the 59 progeny lines analyzed, eight lines contained both the resistance genes, xa5 and Xa4.

Mol Genet Genomics, 2001 Sep, 266(1), 79 - 95
Lipopolysaccharide biosynthesis in Xanthomonas campestris pv . campestris: a cluster of 15 genes is involved in the biosynthesis of the LPS O-antigen and the LPS core; Vorholter FJ et al.; As a result of mutational and DNA sequence analysis, a wxc gene cluster involved in the synthesis of the surface lipopolysaccharide (LPS) was identified in Xanthomonas campestris pv . campestris . This gene cluster comprises 15 genes . It was located on a cloned 35-kb fragment of chromosomal DNA, close, but not directly adjacent, to previously characterized genes for LPS biosynthesis . The G + C content of all but one of the wxc genes was atypically low for X . campestris pv . campestris, while the G + C distribution was uniform throughout the cluster . An SDS-PAGE analysis of mutant strains defective in various wxc genes confirmed that genes from this cluster were involved in LPS biosynthesis . The mutant phenotypes allowed the differentiation of three regions within the wxc cluster . Genes from wxc region 1 are necessary for the biosynthesis of the water-soluble LPS O-antigen . Analysis of DNA and deduced amino acid sequences led to the identification of two glycosyltransferases, two components of an ABC transport system, and a possible kinase among the seven putative proteins encoded by genes constituting wxc region 1 . The two genes in wxc region 2 were similar to gmd and rmd, which direct the synthesis of the sugar nucleotide GDP-D-rhamnose . Mutations affecting wxc region 2 demonstrated its involvement in the formation of the LPS core . Genes from wxc region 3 showed similarities to genes that code for enzymes that modify nucleotide sugars, and to components of sugar translocation systems that have so far been rarely described in bacteria.

FEMS Microbiol Lett, 2001 Sep 25, 203(2), 165 - 71
Fastidian gum: the Xylella fastidiosa exopolysaccharide possibly involved in bacterial pathogenicity; da Silva FR et al.; The Gram-negative bacterium Xylella fastidiosa was the first plant pathogen to be completely sequenced . This species causes several economically important plant diseases, including citrus variegated chlorosis (CVC) . Analysis of the genomic sequence of X . fastidiosa revealed a 12 kb DNA fragment containing an operon closely related to the gum operon of Xanthomonas campestris . The presence of all genes involved in the synthesis of sugar precursors, existence of exopolysaccharide (EPS) production regulators in the genome, and the absence of three of the X . campestris gum genes suggested that X . fastidiosa is able to synthesize an EPS different from that of xanthan gum . This novel EPS probably consists of polymerized tetrasaccharide repeating units assembled by the sequential addition of glucose-1-phosphate, glucose, mannose and glucuronic acid on a polyprenol phosphate carrier.

Mol Microbiol, 2001 Sep, 41(6), 1271 - 81
cDNA-AFLP analysis unravels a genome-wide hrpG-regulon in the plant pathogen Xanthomonas campestris pv . vesicatoria; Noel L et al.; The Hrp type III protein secretion system is essential for pathogenicity of the Gram-negative plant pathogen Xanthomonas campestris pv . vesicatoria . Expression of the hrp gene cluster is controlled by HrpG, a two-component response regulator, and HrpX, an AraC-type transcriptional activator . Using the cDNA-AFLP technique, 30 hrpG-induced (hgi) and five hrpG-repressed (hgr) cDNA fragments were identified, defining a large hrpG-regulon in X . campestris pv . vesicatoria . Expression of most genes in the hrpG-regulon was dependent on hrpX . Seven cDNA fragments map to the known hrp gene cluster and flanking regions . All other genes appear to be scattered over the chromosome and endogenous plasmids . Sequence analysis identified genes encoding putative extracellular proteases, a putative transcriptional regulator and XopJ and XopB (Xanthomonas outer proteins), homologues of YopJ from Yersinia spp . and the avirulence protein AvrPphD of Pseudomonas syringae respectively . XopB is secreted by the Hrp type III secretion system . Analysis of deletion mutants in several hgi genes revealed a new virulence locus . This study demonstrates that cDNA-AFLP is a powerful tool to study prokaryotic transcriptomes and to identify genes contributing to Xanthomonas virulence and putative effector proteins.

Plant Mol Biol, 2001 Aug, 46(6), 661 - 71
Molecular cloning of a novel pathogen-inducible cDNA encoding a putative acyl-CoA synthetase from Capsicum annuum L; Lee SJ et al.; By means of differential display, a pool of salicylic acid (SA)-induced mRNAs were identified and subsequently their cDNAs were isolated from a cDNA library prepared from SA-induced leaf tissues of hot pepper . One of these cDNA clones, designated CaSIG4, was 1900 bp and contained an open reading frame encoding 523 amino acids with a calculated molecular mass of 56.3 kDa . The predicted amino acid sequence of CaSIG4 showed high sequence similarity to the AMP-binding protein family of both prokaryotic and eukaryotic acyl-CoA synthetases . CaSIG4 transcripts accumulated rapidly after SA treatment and in response to both incompatible and compatible interactions with Xanthomonas campestris pv . vesicatoria race 1 . To investigate the cis-acting elements mediating CaSIG4 expression, the CaSIG4 5'-flanking region was isolated by inverse PCR . Database searches indicated that a potential cis-regulatory element is almost identical to the consensus core sequences ACC(A/T)ACC(A/C) which are conserved among promoters of other phenylpropanoid biosynthetic genes . The subcellular localization of the CaSIG4 protein was studied by using a soluble modified GFP gene fusion delivered into epidermal cells of onion by biolistic bombardment . The CaSIG4-smGFP fusion protein was localized to the plasma membrane . Taken together, CaSIG4 encoding a putative acyl-CoA synthetase could function as a plasma membrane-bound protein with a role in signaling in plant defense.

FEMS Microbiol Lett, 2001 Sep 11, 203(1), 11 - 21
Novel domains of the prokaryotic two-component signal transduction systems; Galperin MY et al.; The archetypal two-component signal transduction systems include a sensor histidine kinase and a response regulator, which consists of a receiver CheY-like domain and a DNA-binding domain . Sequence analysis of the sensor kinases and response regulators encoded in complete bacterial and archaeal genomes revealed complex domain architectures for many of them and allowed the identification of several novel conserved domains, such as PAS, GAF, HAMP, GGDEF, EAL, and HD-GYP . All of these domains are widely represented in bacteria, including 19 copies of the GGDEF domain and 17 copies of the EAL domain encoded in the Escherichia coli genome . In contrast, these novel signaling domains are much less abundant in bacterial parasites and in archaea, with none at all found in some archaeal species . This skewed phyletic distribution suggests that the newly discovered complexity of signal transduction systems emerged early in the evolution of bacteria, with subsequent massive loss in parasites and some horizontal dissemination among archaea . Only a few proteins containing these domains have been studied experimentally, and their exact biochemical functions remain obscure; they may include transformations of novel signal molecules, such as the recently identified cyclic diguanylate . Recent experimental data provide the first direct evidence of the participation of these domains in signal transduction pathways, including regulation of virulence genes and extracellular enzyme production in the human pathogens Bordetella pertussis and Borrelia burgdorferi and the plant pathogen Xanthomonas campestris . Gene-neighborhood analysis of these new domains suggests their participation in a variety of processes, from mercury and phage resistance to maintenance of virulence plasmids . It appears that the real picture of the complexity of phosphorelay signal transduction in prokaryotes is only beginning to unfold.

Lett Appl Microbiol, 2001 Sep, 33(3), 183 - 7
Utilization of chicory roots for microbial endoinulinase production; Park JP et al.; AIMS: The optimal culture conditions for endoinulinase production using chicory roots were studied in shake-flask culture . METHODS AND RESULTS: Much higher enzyme production was achieved with Xanthomonas sp . (15 U ml(-1)) than with Pseudomonas sp . (3 U ml(-1)) . Optimized culture conditions of Xanthomonas sp . for endoinulinase production in flask culture were: chicory powder, 5 g l(-1); temperature, 37 degrees C; pH, 7.0; agitation speed, 100 rev min(-1) . CONCLUSION: Maximum bacterial growth and enzyme production were 6.2 g l(-1) and 20 U ml(-1) under optimal conditions, respectively . SIGNIFICANCE AND IMPACT OF THE STUDY: Chicory roots could be used as a fermentation substrate for the production of enndoinulinase.

Biochem Biophys Res Commun, 2001 Sep 21, 287(2), 550 - 5
UDP-glucose dehydrogenase gene of Xanthomonas campestris is required for virulence; Chang KW et al.; Xanthomonas campestris pv . campestris (Xc) is the casual agent of black rot in crucifers . The Xc gene (udgH) coding for UDP-glucose dehydrogenase, an enzyme catalyzing the conversion of UDP-glucose to UDP-glucuronic acid, was previously shown to be required for the biosynthesis of xanthan gum, a substance necessary for the bacterium to cause disease . In this study, the transcription start site of the udgH was determined and the promoter activity monitored by the xylE reporter system indicated that expression of the udgH increases following cell growth and that the udgH gene may possess a second promoter that is responsive to stationary-phase change retaining high levels of expression . Results of Southern hybridization suggest that the udgH gene may be ubiquitous in Xanthomonas, coincident with the notion that members of this genus are capable of xanthan gum biosynthesis . Mutation of the udgH gene in Xc and X . campestris pv . vesicatoria, the casual agent of leaf spot in pepper and tomato, was found to cause a loss of virulence .

Appl Microbiol Biotechnol, 2001 Aug, 56(3-4), 435 - 41
Detection of Xanthomonas oryzae pv . oryzae in artificially inoculated and naturally infected rice seeds and plants by molecular techniques; Sakthivel N et al.; A polymerase chain reaction (PCR) technique was developed for detecting the presence of Xanthomonas oryzae pv . oryzae, the bacterial leaf blight (BLB) pathogen in rice seed and for studying the transmission of this bacterium from seed to plant . Primers TXT and TXT4R from an insertion sequence (IS1113) of the pathogen were used to amplify a 964-bp DNA fragment . A combined biological and enzymatic amplification (BIO-PCR) technique was used to detect the pathogen in naturally infected seed . The level of detection of TXT and TXT4R primers was 55 fg DNA of X . o . pv . oryzae, which is roughly the equivalent of seven cells (and four cells in pure culture suspension) of X . o . pv . oryzae . Hybridization of IS1113 with the amplified DNA fragment in Southern blot analysis confirmed that the 964-bp DNA fragment was amplified from X . o . pv . oryzae . The presence of the IS1113 element in strains of X . o . pv . oryzae from 16 rice-growing countries was confirmed by DNA dot blot analysis . X . o . pv . oryzae was detected from the seed washes and DNA extracted from the seed washes of naturally infected seeds of cvs Jaya and TN1 . When stored at 4 degrees C, the pathogen was recovered up to 4 months and 9 months from naturally infected seeds of cvs Jaya and TN1, respectively . The BLB bacterium was also detected in seedlings, mature plants and seeds collected from plants raised from naturally infected seeds.

J Mol Microbiol Biotechnol, 2001 Oct, 3(4), 519 - 28
Sequence, transcriptional analysis and chromosomal location of the Xanthomonas campestris pv . campestris uvrB gene; Lee TC et al.; The uvrB gene of Xanthomonas campestris pv . campestris, a Gram-negative plant pathogenic bacterium inhabiting soil and infected plants, was cloned and sequenced . This gene has the capacity to encode a polypeptide of 673 amino acid residues with a calculated molecular mass of 75.9 kDa . Its deduced amino acid sequence shows a high degree of similarity and possesses domain conservation to those of bacterial UvrB . The uvrB mutant, isolated by gene replacement, is extremely sensitive to ultraviolet irradiation . Like the situation in the X . campestris pv . campestris recA gene, no SOS box is present upstream of the uvrB gene . Northern blotting and transcriptional fusion assay with lacZ indicated that X . campestris pv . campestris uvrB is expressed constitutively at high levels and cannot be further induced by UV irradiation . These results suggest a regulatory mechanism different from that for the expression of Escherichia coli uvrB . Using a gene-tagging strategy in conjunction with pulsed-field gel electrophoresis, the uvrB gene was located near 1 o'clock on the X . campestris pv . campestris 17 chromosome (4.8 Mb) map, which is far apart from the lexA-recA-recX cluster near 5 o'clock.

Appl Environ Microbiol, 2001 Sep, 67(9), 4105 - 10
gly gene cloning and expression and purification of glycinecin A, a bacteriocin produced by Xanthomonas campestris pv . glycines 8ra; Heu S et al.; Glycinecin A, a bacteriocin produced by Xanthomonas campestris pv . glycines, inhibits the growth of X . campestris pv . vesicatoria . We have cloned and expressed the genes encoding glycinecin A in Escherichia coli . Recombinant glycinecin A was purified from cell extracts by ammonium sulfate precipitation followed by chromatography on Q-Sepharose, Mono Q (ion exchange), and size exclusion columns . Purified glycinecin A is composed of two polypeptides, is active over a wide pH range (6 to 9), and is stable at temperatures up to 60 degrees C . Glycinecin A is a heterodimer consisting of 39- and 14-kDa subunits, as revealed through size exclusion chromatography and cross-linking analysis . Two genes, glyA and glyB, encoding the 39- and 14-kDa subunits, respectively, were identified based on the N-terminal sequences of the subunits . From the nucleotide sequences of glyA and glyB, we conclude that both genes are translated as bacteriocin precursors that include N-terminal leader sequences . When expressed in E . coli, recombinant glycinecin A was found primarily in cell extracts . In contrast, most glycinecin A from Xanthomonas was found in the culture media . E . coli transformed with either glyA or glyB separately did not show the bacteriocin activity.

Appl Microbiol Biotechnol, 2001 Jun, 55(6), 782 - 6
Exopolysaccharides of Xanthomonas pathovar strains that infect rice and wheat crops; Sunish Kumar R et al.; In order to understand the mode of action of the taxonomically related pathogens Xanthomonas campestris pv . translucens, Xanthomonas oryzae pv . oryzae, and Xanthomonas oryzae pv . oryzicola, which attack wheat and rice crops, we examined the compositional differences of their exopolysaccharides (EPSs) . Maximum production of polysaccharide in shake cultures of these pathogens was observed between 24 and 72 h . X . campestris pv . translucens, the leaf streak pathogen of wheat, produced a higher amount of polysaccharide (46.97 microg/ml) at 72 h compared to X . oryzae pv . oryzae (42.02 microg/ml), the bacterial blight pathogen of rice, and X . oryzae pv . oryzicola (41.91 microg/ml), the bacterial leaf streak pathogen of rice . Infrared (FTIR) spectra suggested that the polysaccharides of all three Xanthomonas pathovar strains have an -OH group with intermolecular hydrogen bonding, a C-H group of methyl alkanes, an aldehyde (RCHO) group, a C=C or C=O group, and a C-O group . FTIR spectra also revealed the presence of an acid anhydride group in X . oryzae pv . oryzae, a secondary aromatic or aliphatic amine group in X . campestris pv . translucens, and a primary aromatic or aliphatic amine group in X . oryzae pv . oryzae and X . oryzae pv . oryzicola . Nuclear magnetic resonance (NMR) spectra revealed the presence of unsubstituted sugars, an acetyl amine of hexose or pentose, and a beta-anomeric carbon of hexose or pentose in the polysaccharides of all bacteria . NMR spectra also identified the alpha-anomeric carbon of hexose or pentose in all strains, and a branching at the fourth carbon of the sugar only in X . campestris pv . translucens; the presence of an uronic acid molecule (acid anhydride group) in X . oryzae pv . oryzae; and a deoxy sugar, rhamnose, in X . oryzae pv . oryzicola.

Appl Microbiol Biotechnol, 2001 Jun, 55(6), 727 - 33
Xanthomonas campestris pv . campestris secretes the endoglucanases ENGXCA and ENGXCB: construction of an endoglucanase-deficient mutant for industrial xanthan production; Schroter K et al.; Xanthomonas campestris pv . campestris secretes at least two cellulose-degrading endoglucanases . One of these endoglucanases is encoded by the engXCA gene of X . c . pv . campestris 8400 that was previously characterized by Gough et al . {Gene (1990) 89: 53-59} . An additional endoglucanase encoded by the engXCB gene was identified in X . c . pv . campestris 8400 and FC2 . The engXCB gene product that was grouped into the endoglucanase family E contains a putative N-terminal signal peptide, suggesting a secretion by the type II secretion system . The ENGXCB protein contributed approximately 8% to the cellulase activity in xanthan preparations . Deletion of engXCA and engXCB resulted in a fivefold reduction of the cellulose-degrading activity in xanthan preparations . The cellulase activity determined in xanthan preparations of the engXCA-engXCB mutant was only slightly higher than the activity found in preparations that were subjected to heat treatment . Mutations in engXCA and engXCB did not affect the growth rate and xanthan production of X . c . pv . campestris FC2 under several cultivation conditions . The engXCA-engXCB deletion mutant is markerless, which makes this mutant a valuable strain for xanthan production and approaches aimed at inactivating further genes encoding extracellular enzymes.

FEMS Microbiol Rev, 2001 Aug, 25(4), 365 - 404
Quorum-sensing in Gram-negative bacteria; Whitehead NA et al.; It has become increasingly and widely recognised that bacteria do not exist as solitary cells, but are colonial organisms that exploit elaborate systems of intercellular communication to facilitate their adaptation to changing environmental conditions . The languages by which bacteria communicate take the form of chemical signals, excreted from the cells, which can elicit profound physiological changes . Many types of signalling molecules, which regulate diverse phenotypes across distant genera, have been described . The most common signalling molecules found in Gram-negative bacteria are N-acyl derivatives of homoserine lactone (acyl HSLs) . Modulation of the physiological processes controlled by acyl HSLs (and, indeed, many of the non-acyl HSL-mediated systems) occurs in a cell density- and growth phase-dependent manner . Therefore, the term 'quorum-sensing' has been coined to describe this ability of bacteria to monitor cell density before expressing a phenotype . In this paper, we review the current state of research concerning acyl HSL-mediated quorum-sensing . We also describe two non-acyl HSL-based systems utilised by the phytopathogens Ralstonia solanacearum and Xanthomonas campestris.

Biosci Biotechnol Biochem, 2001 Jul, 65(7), 1684 - 7
Cloning and nucleotide sequence of the mycodextranase gene from Streptomyces sp . J-13-3; Okazaki K et al.; Mycodextranase (EC 3.2.1.61) is an alpha-glucanase that cleaves alpha-1,4-bonds of alternating alpha-1,3- and alpha-1,4-linked D-glucan (nigeran) . The gene encoding mycodextranase from Streptomyces sp . J-13-3 was cloned by hybridization with a degenerate oligonucleotide probe from the amino-terminal amino acid sequence of the enzyme and its nucleotide structure was analyzed . The open reading frame consisted of 1,803 base pairs encoding a signal peptide of 60 amino acids and a mature protein of 540 amino acids with a calculated molecular weight of 56,078 . The deduced amino acid sequence showed weak similality to a chitinase homolog from Streptomyces lividans and a chitinase from Xanthomonas sp.

Folia Microbiol (Praha), 2000, 45(6), 531 - 7
Some tryptophan pathways in the phytopathogen Xanthomonas oryzae pv . oryzae; Ansari MM et al.; Xanthomonas oryzae pv . oryzae, the causal organism of bacterial blight of rice which produces leaf blight as well as kresek (wilt) symptoms in plants were tested for indole, auxin production in culture supplemented with L-tryptophan . On the basis of indoleacetic acid (IAA) production the isolates were grouped into IAA-positive and IAA-negative . Out of 17 isolates, 11 were IAA-positive while 6 were IAA-negative . The isolates metabolized tryptophan through two different routes and the isolates vary in the pathway of tryptophan utilization . The IAA-positive isolates converted tryptophan to IAA as the end product, whereas the IAA-negative isolates formed anthranilate as an intermediate metabolite and finally produced pyrocatechol via the kynurenine pathway . Quantification of tryptophan metabolism revealed that the maximum production of IAA and pyrocatechol in culture occurred during 2-d incubation at 30 +/- 2 degrees C.

Plant J, 2001 Jul, 27(2), 101 - 13
Evidence for a disease-resistance pathway in rice similar to the NPR1-mediated signaling pathway in Arabidopsis; Chern MS et al.; The Arabidopsis NPR1/NIM1 gene is a key regulator of systemic acquired resistance (SAR) . Over-expression of NPR1 leads to enhanced resistance in Arabidopsis . To investigate the role of NPR1 in monocots, we over-expressed the Arabidopsis NPR1 in rice and challenged the transgenic plants with Xanthomonas oryzae pv . oryzae (Xoo), the rice bacterial blight pathogen . The transgenic plants displayed enhanced resistance to Xoo . RNA blot hybridization indicates that enhanced resistance requires expression of NPR1 mRNA above a threshold level in rice . To identify components mediating the resistance controlled by NPR1, we used NPR1 as bait in a yeast two-hybrid screen . We isolated four cDNA clones encoding rice NPR1 interactors (named rTGA2.1, rTGA2.2, rTGA2.3 and rLG2) belonging to the bZIP family . rTGA2.1, rTGA2.2 and rTGA2.3 share 75, 76 and 78% identity with Arabidopsis TGA2, respectively . In contrast, rLG2 shares highest identity (81%) to the maize liguleless (LG2) gene product, which is involved in establishing the leaf blade-sheath boundary . The interaction of NPR1 with the rice bZIP proteins in yeast was impaired by the npr1-1 and npr1-2 mutations, but not by the nim1-4 mutation . The NPR1-rTGA2.1 interaction was confirmed by an in vitro pull-down experiment . In gel mobility shift assays, rTGA2.1 binds to the rice RCH10 promoter and to a cis-element required sequence-specifically for salicylic acid responsiveness . This is the first demonstration that the Arabidopsis NPR1 gene can enhance disease resistance in a monocot plant . These results also suggest that monocot and dicot plants share a conserved signal transduction pathway controlling NPR1-mediated resistance.

Arch Microbiol, 2001 Jul, 176(1-2), 121 - 8
Characterization of stress-responsive genes, hrcA-grpE-dnaK-dnaJ, from phytopathogenic Xanthomonas campestris; Weng SF et al.; Sequencing of a 6.4-kb DNA fragment, cloned from the plant pathogenic bacterium Xanthomonas campestris pv . campestris 17 revealed five ORFs whose deduced amino acid sequences show strong similarities to the bacterial HrcA, GrpE, DnaK, DnaJ, and PdxK . The four heat shock genes are organized in the order hrcA-grpE-dnaK-dnaJ, a genome organization found in many gram-positive bacteria, but only in one gram-negative species (Xylella fastidiosa) . These observations suggest that the HrcA-CIRCE system, comprising at least four genes arranged in this order, already existed for the regulation of stress responses before bacteria diverged into gram-negative and gram-positive groups . Primer-extension results suggested the presence of promoters at the regions upstream of grpE and dnaK . In the presence of stress, heat or ethanol (4%), the X . campestris pv . campestris 17 grpE and dnaK promoters were induced two- to three-fold over controls . Since the grpE and dnaK promoters possess E . coli sigma(32) promoter-like sequences, they are functional in E . coli, although at levels much lower than in X . campestris pv . campestris 17 . Furthermore, expression of the X . campestris pv . campestris 17 dnaK promoter in E . coli was elevated by the cloned X . campestris sigma(32) gene, indicating that the cognate sigma(32) works more efficiently for the X . campestris promoters.

Appl Environ Microbiol, 2001 Aug, 67(8), 3379 - 84
Assessment of the genetic diversity among strains of Xanthomonas cynarae by randomly amplified polymorphic DNA analysis and development of specific characterized amplified regions for the rapid identification of X . cynarae; Trebaol G et al.; The randomly amplified polymorphic DNA (RAPD) method was used to investigate the genetic diversity in Xanthomonas cynarae, which causes bacterial bract spot disease of artichoke . This RAPD analysis was also intended to identify molecular markers characteristic of this species, in order to develop PCR-based markers which can be used to detect this pathogenic bacterium in artichoke fields . Among the 340 RAPD primers tested, 40 were selected on their ability to produce reproducible and reliable fingerprints in our genetic background . These 40 primers produced almost similar patterns for the 37 X . cynarae strains studied, different from the fingerprints obtained for other Xanthomonas species and other xanthomonad-like bacteria isolated from artichoke leaves . Therefore, X . cynarae strains form a homogeneous genetic group . However, a little DNA polymorphism within this species was observed and the collection of X . cynarae isolates was divided into two groups (one containing three strains, the second one including all other strains) . Out of seven RAPD markers characteristic of X . cynarae that were cloned, four did not hybridize to the genomic DNA of strains belonging to other Xanthomonas species . These four RAPD markers were converted into PCR markers (specific characterized amplified regions {SCARs}); they were sequenced, and a PCR primer pair was designed for each of them . Three derived SCARs are good candidates to develop PCR-based tests to detect X . cynarae in artichoke fields.

J Biotechnol, 2001 Jul 26, 89(1), 55 - 63
Polysaccharide synthesis as a carbon dissipation mechanism in metabolically uncoupled Xanthomonas campestris cells; Esgalhado ME et al.; The utilization of xanthan metabolism as an excess carbon dissipation path in Xanthomonas campestris cells under sub-lethal acid stress was studied . To highlight growth limitation during metabolic uncoupling due to acid toxicity a antibiotic was added . The simultaneous addition of enoxacin and acetic acid showed that the xanthan production per unit of biomass raises with increasing concentrations of enoxacin, which seems to indicate that when the cell is prevented from growing it finds a path to convey the extra carbon . In parallel, although the effect of acetic acid is not very significant, its presence appears to increase xanthan . This tendency seems to be accentuated with increasing concentrations of enoxacin . In fact, in presence of 0.15 mM of acetic acid, 2.88 and 5.76 microM of antibiotic produces xanthan/biomass yields of 8.13 and 9.82 g g(-1) which drop to below half those values (3.55 g g(-1)) when enoxacin is removed . When enoxacin was kept constant, xanthan/biomass yields showed small increments with the increase of acetic acid . Thus, with 1.44, 2.88 and 4.32 microM enoxacin concentrations, the addition of organic acid produces a 6--8% stimulation of xanthan.

J Bacteriol, 2001 Aug, 183(15), 4405 - 12
Complex regulation of the organic hydroperoxide resistance gene (ohr) from Xanthomonas involves OhrR, a novel organic peroxide-inducible negative regulator, and posttranscriptional modifications; Sukchawalit R et al.; Analysis of the sequence immediate upstream of ohr revealed an open reading frame, designated ohrR, with the potential to encode a 17-kDa peptide with moderate amino acid sequence homology to the MarR family of negative regulators of gene expression . ohrR was transcribed as bicistronic mRNA with ohr, while ohr mRNA was found to be 95% monocistronic and 5% bicistronic with ohrR . Expression of both genes was induced by tert-butyl hydroperoxide (tBOOH) treatment . High-level expression of ohrR negatively regulated ohr expression . This repression could be overcome by tBOOH treatment . In vivo promoter analysis showed that the ohrR promoter (P1) has organic peroxide-inducible, strong activity, while the ohr promoter (P2) has constitutive, weak activity . Only P1 is autoregulated by OhrR . ohr primer extension results revealed three major primer extension products corresponding to the 5' ends of ohr mRNA, and their levels were strongly induced by tBOOH treatment . Sequence analysis of regions upstream of these sites showed no typical Xanthomonas promoter . Instead, the regions can form a stem-loop secondary structure with the 5' ends of ohr mRNA located in the loop section . The secondary structure resembles the structure recognized and processed by RNase III enzyme . These findings suggest that the P1 promoter is responsible for tBOOH-induced expression of the ohrR-ohr operon . The bicistronic mRNA is then processed by RNase III-like enzymes to give high levels of ohr mRNA, while ohrR mRNA is rapidly degraded.

Plant J, 2001 Jun, 26(5), 523 - 34
Eukaryotic features of the Xanthomonas type III effector AvrBs3: protein domains involved in transcriptional activation and the interaction with nuclear import receptors from pepper; Szurek B et al.; The AvrBs3 protein of the phytopathogenic bacterium Xanthomonas campestris pv . vesicatoria is targeted to host-plant cells by the bacterial Hrp type III secretion system . In pepper plants containing the Bs3 resistance gene, AvrBs3 induces the hypersensitive response (HR) . AvrBs3 recognition is thought to occur in the plant cell nucleus as HR induction is dependent on nuclear localization signals (NLSs) and an acidic transcription activation domain (AAD) . In a search for AvrBs3-interacting pepper proteins using the yeast two-hybrid system, we have isolated eight different classes of cDNA inserts including two genes for importin alpha proteins . Importin alpha is part of the nuclear import machinery and interacts with AvrBs3 through an NLS in the carboxy-terminus of the protein, both in yeast and in vitro . The mechanism of AvrBs3 recognition was further studied by analysis of the C-terminal AAD . This putative transcription-activation domain was shown to be required for AvrBs3 HR-inducing activity, and could be functionally replaced with the VP16 AAD from the Herpes simplex virus . Our data support the model in which the AvrBs3 effector localizes to the nucleus, where the Bs3-mediated surveillance system of resistant plants detects AvrBs3 through its interference with host gene transcription.

Phytochemistry, 2001 Aug, 57(7), 1187 - 95
Two cinnamoyl-CoA reductase (CCR) genes from Arabidopsis thaliana are differentially expressed during development and in response to infection with pathogenic bacteria; Lauvergeat V et al.; Cinnamoyl-CoA reductase (CCR; EC 1.2.1.44) catalyses the conversion of cinnamoyl-CoAs into their corresponding cinnamaldehydes, i.e . the first step of the phenylpropanoid pathway specifically dedicated to the monolignol biosynthetic branch . In previous work, we described the isolation and characterisation of the first cDNA encoding CCR in Eucalyptus (Lacombe, E., Hawkins, S., Van Dorsselaere, J., Piquemal, J., Goffner, D., Poeydomenge, O., Boudet, A.M., Grima-Pettenati, J., 1997 . Cinnamoyl CoA reductase, the first committed enzyme of the lignin branch biosynthetic pathway: cloning, expression and phylogenetic relationships . Plant Journal 11, 429--441) and shown the role of this enzyme in controlling the carbon flux into lignins (Piquemal, J., Lapierre, C., Myton, K., O'Connell, A., Schuch, W., Grima-Pettenati, J., Boudet, A.M., 1998 . Down-regulation of cinnamoyl-CoA reductase induces significant changes of lignin profiles in transgenic tobacco plants . Plant Journal 13, 71--83) . Here, we report the characterisation of two functionally and structurally distinct cDNA clones, AtCCR1 and AtCCR2 (81.6% protein sequence identity) in Arabidopsis thaliana . The two recombinant proteins expressed in Escherichia coli are able to use the three cinnamoyl-CoAs tested but with different levels of efficiency . AtCCR1 is five times more efficient with feruloyl-CoA and sinapoyl-CoA than AtCCR2 . In addition, the two genes are differentially expressed during development and in response to infection . AtCCR1 is preferentially expressed in tissues undergoing lignification . In contrast, AtCCR2, which is poorly expressed during development, is strongly and transiently induced during the incompatible interaction with Xanthomonas campestris pv . campestris leading to a hypersensitive response . Altogether, these data suggest that AtCCR1 is involved in constitutive lignification whereas AtCCR2 is involved in the biosynthesis of phenolics whose accumulation may lead to resistance.

Microbiology, 2001 Jul, 147(Pt 7), 1775 - 82
Bacterial Ohr and OsmC paralogues define two protein families with distinct functions and patterns of expression; Atichartpongkul S et al.; Xanthomonas campestris Ohr (a protein involved in organic peroxide protection) and Escherichia coli OsmC (an osmotically inducible protein of unknown function) are related proteins . Database searches and phylogenetic analyses reveal that Ohr and OsmC homologues cluster into two related subfamilies of proteins widely distributed in both Gram-negative and Gram-positive bacteria . To determine if these two subfamilies are functionally distinct, ohr and osmC in Pseudomonas aeruginosa (a bacterium with one representative from each subfamily) were analysed . Only ohr mutants are hypersensitive to organic peroxide, and this phenotype can be restored by complementation with ohr but not osmC . In addition, expression of ohr was highly induced only by organic peroxides, and not by other oxidants or stresses . In contrast, osmC was induced by ethanol and osmotic stress . A similar pattern of regulation was observed for Ohr and OsmC homologues in the Gram-positive bacterium Deinococcus radiodurans, though uninduced expression was much higher and induction lower in this species . These data clearly support the conclusion that Ohr and OsmC define two functionally distinct subfamilies with distinct patterns of regulation.

Carbohydr Res, 2001 Jun 22, 333(1), 7 - 17
The identification of the catalytic nucleophiles of two beta-galactosidases from glycoside hydrolase family 35; Blanchard JE et al.; The beta-galactosidases from Xanthomonas manihotis (beta-Gal Xmn) and Bacillus circulans (beta-Gal-3 Bcir) are retaining glycosidases that hydrolyze glycosidic bonds through a double displacement mechanism involving a covalent glycosyl-enzyme intermediate . The mechanism-based inactivator 2,4-dinitrophenyl 2-deoxy-2-fluoro-beta-D-galactopyranoside was shown to inactivate beta-Gal Xmn and beta-Gal-3 Bcir through the accumulation of 2-deoxy-2-fluorogalactosyl enzyme intermediates with half lives of 40 and 625 h, respectively . Peptic digestion of these labeled enzymes and analysis by LC-MS identified Glu(260) and Glu(233) as the catalytic nucleophiles involved in the formation of the glycosyl-enzyme intermediate during catalysis by beta-Gal Xmn and beta-Gal-3 Bcir, respectively . These findings confirm the previous prediction of the position of these residues based on primary sequence similarities to other members of the glycoside hydrolase family 35.

Biochemistry (Mosc), 2001 Jun, 66(6), 662 - 6
Influence of acidic exopolysaccharide of Xanthomonas campestris IBPM 124 on the kinetic parameters of extracellular bacteriolytic enzymes; Stepnaya OA et al.; Interactions of a negatively charged exopolysaccharide of Xanthomonas campestris IBPM 124 with its extracellular enzymes (muramidase, endopeptidase, and neutral phosphatase) and also with egg lysozyme, lysostaphin, muramidase of Streptomyces globisporus, and a bacteriolytic enzyme complex of Streptomyces albus were studied . All these enzymes were positively charged under the conditions of their maximal activity . It was shown that interaction of the acidic exopolysaccharide from X . campestris with these enzymes changed their kinetic parameters . The change was either positive (increase in reaction rate) or negative (decrease in reaction rate) and depended on the enzyme and type of substrate cleaved . Due to such interactions, the acidic exopolysaccharide secreted by X . campestris into the environment not only retained and transported positively charged exoenzymes into the near-cellular space, but also regulated their activity.

J Bacteriol, 2001 Jul, 183(14), 4134 - 41
OhrR is a repressor of ohrA, a key organic hydroperoxide resistance determinant in Bacillus subtilis; Fuangthong M et al.; Bacillus subtilis displays a complex adaptive response to the presence of reactive oxygen species . To date, most proteins that protect against reactive oxygen species are members of the peroxide-inducible PerR and sigma(B) regulons . We investigated the function of two B . subtilis homologs of the Xanthomonas campestris organic hydroperoxide resistance (ohr) gene . Mutational analyses indicate that both ohrA and ohrB contribute to organic peroxide resistance in B . subtilis, with the OhrA protein playing the more important role in growing cells . Expression of ohrA, but not ohrB, is strongly and specifically induced by organic peroxides . Regulation of ohrA requires the convergently transcribed gene, ohrR, which encodes a member of the MarR family of transcriptional repressors . In an ohrR mutant, ohrA expression is constitutive, whereas expression of the neighboring ohrB gene is unaffected . Selection for mutant strains that are derepressed for ohrA transcription identifies a perfect inverted repeat sequence that is required for OhrR-mediated regulation and likely defines an OhrR binding site . Thus, B . subtilis contains at least three regulons (sigma(B), PerR, and OhrR) that contribute to peroxide stress responses.

Environ Sci Technol, 2001 Jun 1, 35(11), 2275 - 81
Incipient erosion of biostabilized sediments examined using particle-field optical holography; Black KS et al.; Laser holography allows images of three-dimensional space at ultra-high resolution to be recorded onto photographic plates . Recorded scenes can be "replayed" with a second laser beam into free space and optically "interrogated" using either a microscope or a camera by sequentially focusing on increasing distances from the hologram in the field of view (optical sectioning) . From these sections, information on the relative locations and orientation in space of suspended particles as well as the morphology of particles can be obtained . This paper examines the utility of "in-line" laser holography to discriminate the size and the morphology of sand particles eroded under turbulent shear flow during benthic sediment transport . The influence of a commercially available adhesive polymer (xanthan gum, derived from the bacterium Xanthomonas campestris) on sediment stability and resuspended particle morphology is described . The major implications for carbon and sediment cycling within estuaries are highlighted.

J Agric Food Chem, 2001 Jun, 49(6), 2799 - 803
Broad-spectrum antimicrobial activity in vitro of the synthetic peptide D4E1; Rajasekaran K et al.; Broad-spectrum antimicrobial activity of a synthetic peptide, D4E1, is documented in this paper . D4E1 inhibited the growth of several fungal phytopathogens belonging to four classes-Ascomycetes, Basidiomycetes, Deuteromycetes, and Oomycetes, and two bacterial pathogens, Pseudomonas syringae pv . tabaci and Xanthomonas campestris pv . malvacearum race 18 . The minimum inhibitory concentration (MIC) of D4E1 required to completely inhibit the growth of all fungi studied ranged from 4.67 to 25 microM . Fungal pathogens highly sensitive to D4E1 include Thielaviopsis basicola, Verticillium dahliae, Fusarium moniliforme, Phytophthora cinnamomi, and Phytophthora parasitica . Comparatively, the least sensitive fungal pathogens were Alternaria alternata, Colletotrichum destructivum, and Rhizoctonia solani . The two bacterial pathogens, P . syringae pv . tabaci and X . campestris pv . malvacearum race 18, were most sensitive to D4E1 with MIC values of 2.25 and 1.25 microM, respectively . Microscopic analysis of D4E1 effects on fungal morphology of Aspergillus flavus and R . solani revealed abnormal hyphal growth and discontinuous cytoplasm . After 8 h of exposure to 25 microM D4E1, A . flavus spore germination was reduced by 75% . The suitability of peptide D4E1 to enhance disease resistance in transgenic crop plants is discussed.

FEMS Microbiol Lett, 2001 Jun 12, 200(1), 59 - 65
Construction and characterization of a Xanthomonas oryzae pv . oryzae bacterial artificial chromosome library; Ochiai H et al.; Xanthomonas oryzae pv . oryzae is an important plant pathogen which causes bacterial blight of rice . To facilitate genome studies of this bacterium, we have constructed a bacterial artificial chromosome (BAC) library of strain MAFF 311018 . It consisted of 750 clones representing 16 genome equivalents, and had an insert size ranging from 20 to 220 kb with an average size of 107 kb . This library is the first to be constructed from a X . oryzae pv . oryzae strain . The usefulness of this library was demonstrated through polymerase chain reaction screening of 11 genes and the 16S--23S rDNA spacer region in a 192-clone subset, representing five genome equivalents . The results obtained showed an average of 5.9 BAC clones per screening . This result is in good agreement with the estimated size of the test library, indicating that the constructed BAC library can be used to facilitate genome analysis of X . oryzae pv . oryzae.

Mol Genet Genomics, 2001 May, 265(3), 469 - 79
Characterization and expression of beta-1,3-glucanase genes in peach; Thimmapuram J et al.; Beta-1,3-glucanase is one of the pathogenesis-related (PR) proteins involved in plant defense responses . A peach beta-1,3-glucanase gene, designated PpGns1, has been isolated and characterized . The deduced amino acid sequence of the product of PpGns indicates that it is a basic isoform (pI 9.8), and contains a putative signal peptide of 38 amino acids but has no C-terminal extension . Amino acid sequence comparisons revealed that PpGns1 is 69% and 67% identical to citrus and soybean beta-1,3-glucanases, respectively . Southern analysis of total genomic DNA also indicates that at least three genes for beta-1,3-glucanases exist in peach, forming a small gene family . Characterization of four additional clones by PCR has identified a second beta-1,3-glucanase gene, PpGns2 . PpGns2 has been partially sequenced, and when compared to PpGns1, it shows high sequence homology, 96% and 99% nucleotide identity in the first and (partial) second exons, respectively . The deduced partial sequence of the PpGns2 product displays only two differences from PpGns1 in the signal peptide and one in the (partial) mature protein (141 amino acids) . The 5'-flanking promoter regions of these two genes share 90% identity in nucleotide sequences interrupted by five major gaps (4-109 nt long) . The promoter region contains various sequences similar to cis-regulatory elements present in different stress-induced plant genes . In leaves and stems of peach shoot cultures grown in vitro, PpGns1 is induced within 12 h after exposure to a culture filtrate of Xanthomonas campestris pv . pruni or ethephon . However, it is not induced following treatment with mercuric chloride.

Appl Microbiol Biotechnol, 2001 May, 55(4), 417 - 22
Kinetic analysis of growth and xanthan gum production with Xanthomonas campestris on sucrose, using sequentially consumed nitrogen sources; Letisse F et al.; A batch fermentation strategy using Xanthomonas campestris ATCC 13951 for xanthan gum production has been established in which all essential medium components are supplied at the onset . This has been achieved using sucrose as sole sugar feedstock . Sequential consumption of nitrogen sources (soybean hydrolysates, ammonium and nitrate salts) was observed to facilitate the further optimisation of the medium . Biomass accumulation was limited by phosphate availability . Xanthan yields of more than 60% (grams of xanthan per gram of sugar) have been obtained with constant acetyl content . However, pyruvyl substitution decreased as the growth rate declined, due to the metabolic constraints specific to phosphate depletion . High rates of carbon conversion into xanthan were observed throughout the culture and the ATP/ADP ratio was not affected by the decline in the specific growth rate.

J Bacteriol, 2001 Jul, 183(13), 4061 - 70
Microbial origin of plant-type 2-keto-3-deoxy-D-arabino-heptulosonate 7-phosphate synthases, exemplified by the chorismate- and tryptophan-regulated enzyme from Xanthomonas campestris; Gosset G et al.; Enzymes performing the initial reaction of aromatic amino acid biosynthesis, 2-keto-3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthases, exist as two distinct homology classes . The three classic Escherichia coli paralogs are AroA(I) proteins, but many members of the Bacteria possess the AroA(II) class of enzyme, sometimes in combination with AroA(I) proteins . AroA(II) DAHP synthases until now have been shown to be specifically dedicated to secondary metabolism (e.g., formation of ansamycin antibiotics or phenazine pigment) . In contrast, here we show that the Xanthomonas campestris AroA(II) protein functions as the sole DAHP synthase supporting aromatic amino acid biosynthesis . X . campestris AroA(II) was cloned in E . coli by functional complementation, and genes corresponding to two possible translation starts were expressed . We developed a 1-day partial purification method (>99%) for the unstable protein . The recombinant AroA(II) protein was found to be subject to an allosteric pattern of sequential feedback inhibition in which chorismate is the prime allosteric effector . L-Tryptophan was found to be a minor feedback inhibitor . An N-terminal region of 111 amino acids may be located in the periplasm since a probable inner membrane-spanning region is predicted . Unlike chloroplast-localized AroA(II) of higher plants, X . campestris AroA(II) was not hysteretically activated by dithiols . Compared to plant AroA(II) proteins, differences in divalent metal activation were also observed . Phylogenetic tree analysis shows that AroA(II) originated within the Bacteria domain, and it seems probable that higher-plant plastids acquired AroA(II) from a gram-negative bacterium via endosymbiosis . The X . campestris AroA(II) protein is suggested to exemplify a case of analog displacement whereby an ancestral aroA(I) species was discarded, with the aroA(II) replacement providing an alternative pattern of allosteric control . Three subgroups of AroA(II) proteins can be recognized: a large, central group containing the plant enzymes and that from X . campestris, one defined by a three-residue deletion near the conserved KPRS motif, and one possessing a larger deletion further downstream.

What Is Environmental Microbiology?, What Is Prokaryote?, What Is Water Purification?, What Is Genome?, What Is Biofilm?, i, Microorganism, c, Microbe, n, Bacteriology, i, Microorganisms, i, Microbiology, c, S. cerevisiae, e, Pediococci, e, Vancomycin, i, Microbiological, i, Yeasts, c, Yeasts, r, Escherichia coli, n, S. cerevisiae, e, Pediococci, a, Staphylococcus aureus, i, Escherichia coli, r, Staphylococcus, s, Escherichia coli, s, Prokaryotes, a, Wastewater treatment, i, Escherichia coli, r, Microorganisms, c, Bacillus, a, S. cerevisiae, r, Klebsiella, i, Escherichia coli

Scientific Publications - Work Done by Microbiology Reader Bioscreen C
Agricultural Microbiology Anaerobic Microbiology Antimicrobial Susceptibility Artificial Atmosphere Bioassay of Antibiotics Biofilm Microbiology Bioreactor Technology Biotechnology Cell Biology Clinical Microbiology Environmental Microbiology Experiments with Yeast	Fermentation Food Microbiology Functional Genomics Gene Technology Growth Media Development Growth Rate and Lag Time Industrial Microbiology Medical/Pharmaceutical Field Microbiological Assay Microbiological Research Microbiology of Cosmetics go to a specific theme...	Military Microbiology Molecular Microbiology Mutagenicity and Genotoxicity Oral Microbiology Patents Postantibiotic Studies Soil Microbiology Spore Microbiology Veterinary Microbiology Waste/Wastewater Treatment Water Microbiology Wine Microbiology

� 2005 Transgalactic Ltd (manufacturer of Bioscreen C software) | Privacy Statement | P.O. Box 1393, 00101 Helsinki, Finland, phone: +358 9 85172920, fax: +358 9 8749481, e-mail: microbiology@bionewsonline.com

Last modified: May 25, 2005