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Transcriptional Regulation of the phoPR Operon in Bacillus subtilis. Zoltán Prágai, 2004. When Bacillus subtilis is subjected to phosphate starvation, the Pho regulon is activated by the PhoP-PhoR two-componentsignal transduction system to elicit specific responses to thisnutrient limitation . The response regulator, PhoP, and its cognatehistidine sensor kinase, PhoR, are encoded by the phoPR operonthat is transcribed as a 2.7-kb bicistronic mRNA . The phoPRoperon is transcribed from two  A-dependent
promoters, P1 andP2 . Under conditions where
the Pho regulon was not induced [i.e.,phosphate-replete conditions
or phoR-null mutant], a low levelof phoPR
transcription was detected only from promoter P1 . During
phosphate starvation-induced transition from exponential to
stationary phase, the expression of the phoPR operon was up-regulated
in a phosphorylated PhoP [PhoP P]-dependent
manner; in additionto P1, the P2 promoter
becomes active . In vitro gel shift assaysand DNase I footprinting
experiments showed that both PhoP andPhoPP
could bind to the control region of the phoPR operon.The data
indicate that while low-level constitutive expressionof phoPR
is required under phosphate-replete conditions forsignal perception
and transduction, autoinduction is requiredto provide sufficient
PhoPP
to induce other members of the Phoregulon . The extent to which
promoters P1 and P2 are activatedappears to be
influenced by the presence of other sigma factors,possibly the
result of sigma factor competition . For example,phoPR is
hyperinduced in a sigB mutant and, later in stationaryphase,
in sigH, sigF, and sigE mutants . The data point to a
complex regulatory network in which other stress responses and
post-exponential-phase processes influence the expression ofphoPR
and, thereby, the magnitude of the Pho regulon response.
Correlation between In Vitro Susceptibility of Scedosporium apiospermum to Voriconazole and In Vivo Outcome of Scedosporiosis in Guinea Pigs. Javier Capilla, 2004.We have evaluated the efficacy of voriconazole (VRC) in a systemic infection by Scedosporium apiospermum in immunodepressed guinea pigs . Animals were infected with two strains; one required a VRC MIC of 0.5 to 1 µg/ml, common for this fungus, and the other required a high MIC (8 µg/ml), unusual in this species . VRC prolonged survival and reduced fungal load in kidney and brain tissues of the animals infected with the first strain but was unable to prolong survival or to reduce fungal load in brain tissue for the latter strain . Sequence-Selective Recognition of Extended-Spectrum ß-Lactamase GES-2 by a Competitive, Peptide Nucleic Acid-Based Multiplex PCR Assay. Gerhard F. Weldhagen, 2004.Extended-spectrum ß-lactamases (ESBLs) in Pseudomonas aeruginosa, such as GES-2, which compromises the efficacy of imipenem, tend to be geographically restricted . The CC-to-AA base pair substitution at positions 493 and 494 of the blaGES-2-coding region distinguishes this ESBL from blaGES-1 and the blaIBC-type genes, making it an ideal target for the development of a novel sequence-specific, peptide nucleic acid (PNA)-based multiplex PCR detection method . By using two primer pairs in conjunction with a PNA probe, this method provided an accurate means of identification of blaGES-2 compared to standard PCR and gene sequencing techniques when it was used to test 100 P . aeruginosa clinical isolates as well as previously published, well-described control strains encompassing all presently known genes in the blaGES-IBC ESBL family . This novel method has the potential to be used in large-scale, cost-effective screening programs for specific or geographically restricted ESBLs . Combined Immunomagnetic Separation-Molecular Beacon-Reverse Transcription-PCR Assay for Detection of Hepatitis A Virus from Environmental Samples. Khaled H. Abd El Galil, 2004. The PhlA Hemolysin from the Entomopathogenic Bacterium Photorhabdus luminescens Belongs to the Two-Partner Secretion Family of Hemolysins. Julien Brillard, 2002.Photorhabdus is an entomopathogenic bacterium symbiotically associated with nematodes of the family Heterorhabditidae . Bacterial hemolysins found in numerous pathogenic bacteria are often virulence factors . We describe here the nucleotide sequence and the molecular characterization of the Photorhabdus luminescens phlBA operon, a locus encoding a hemolysin which shows similarities to the Serratia type of hemolysins . It belongs to the two-partner secretion (TPS) family of proteins . In low-iron conditions, a transcriptional induction of the phlBA operon was observed by using the chloramphenicol acetyltransferase reporter gene, causing an increase in PhlA hemolytic activity compared to iron-rich media . A spontaneous phase variant of P . luminescens was deregulated in phlBA transcription . The phlA mutant constructed by allelic exchange remained highly pathogenic after injection in the lepidopteran Spodoptera littoralis, indicating that PhlA hemolysin is not a major virulence determinant . Using the gene encoding green fluorescent protein as a reporter, phlBA transcription was observed in hemolymph before insect death . We therefore discuss the possible role of PhlA hemolytic activity in the bacterium-nematode-insect interactions . Characterization of Hydrocarbon-Degrading Microbial Populations in Contaminated and Pristine Alpine Soils. R. Margesin, 2003.Biodegradation of petroleum hydrocarbons in cold environments, including Alpine soils, is a result of indigenous cold-adapted microorganisms able to degrade these contaminants . In the present study, the prevalence of seven genotypes involved in the degradation of n-alkanes (Pseudomonas putida GPo1 alkB; Acinetobacter spp . alkM; Rhodococcus spp . alkB1, and Rhodococcus spp . alkB2), aromatic hydrocarbons (P . putida xylE), and polycyclic aromatic hydrocarbons (P . putida ndoB and Mycobacterium sp . strain PYR-1 nidA) was determined in 12 oil-contaminated (428 to 30,644 mg of total petroleum hydrocarbons [TPH]/kg of soil) and 8 pristine Alpine soils from Tyrol (Austria) by PCR hybridization analyses of total soil community DNA, using oligonucleotide primers and DNA probes specific for each genotype . The soils investigated were also analyzed for various physical, chemical, and microbiological parameters, and statistical correlations between all parameters were determined . Genotypes containing genes from gram-negative bacteria (P . putida alkB, xylE, and ndoB and Acinetobacter alkM) were detected to a significantly higher percentage in the contaminated (50 to 75%) than in the pristine (0 to 12.5%) soils, indicating that these organisms had been enriched in soils following contamination . There was a highly significant positive correlation (P < 0.001) between the level of contamination and the number of genotypes containing genes from P . putida and Acinetobacter sp . but no significant correlation between the TPH content and the number of genotypes containing genes from gram-positive bacteria (Rhodococcus alkB1 and alkB2 and Mycobacterium nidA) . These genotypes were detected at a high frequency in both contaminated (41.7 to 75%) and pristine (37.5 to 50%) soils, indicating that they are already present in substantial numbers before a contamination event . No correlation was found between the prevalence of hydrocarbon-degradative genotypes and biological activities (respiration, fluorescein diacetate hydrolysis, lipase activity) or numbers of culturable hydrocarbon-degrading soil microorganisms; there also was no correlation between the numbers of hydrocarbon degraders and the contamination level . The measured biological activities showed significant positive correlation with each other, with the organic matter content, and partially with the TPH content and a significant negative correlation with the soil dry-mass content (P < 0.05 to 0.001) .
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