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Complete Genomic Nucleotide Sequence of the Temperate Bacteriophage Aa  23
of Actinobacillus actinomycetemcomitans.Grégory Resch, 2004.The entire double-stranded DNA genome of the Actinobacillus actinomycetemcomitans bacteriophage Aa 23
was sequenced . Linear DNA contained in the phage particles is
circularly permuted and terminally redundant . Therefore, the physical
map of the phage genome is circular . Its size is 43,033 bp with an
overall molar G+C content of 42.5 mol% . Sixty-six potential open
reading frames (ORFs) were identified, including an ORF resulting
from a translational frameshift . A putative function could be
assigned to 23 of them . Twenty-three other ORFs share homologies only
with hypothetical proteins present in several bacteria or bacteriophages,
and 20 ORFs seem to be specific for phage Aa23 .
The organization of the phage genome and several genetic functions
share extensive similarities to that of the lambdoid phages . However,
Aa23
encodes a DNA adenine methylase, and the DNA packaging strategy is
more closely related to the P22 system . The attachment sites of Aa23
(attP) and several A . actinomycetemcomitans hosts (attB)
are 49 bp long .
Epiphytic Cyanobacteria on Chara vulgaris Are the Main Contributors to N2 Fixation in Rice Fields. Yoanna Ariosa, 2004.The distribution of nitrogenase activity in the rice-soil system and the possible contribution of epiphytic cyanobacteria on rice plants and other macrophytes to this activity were studied in two locations in the rice fields of Valencia, Spain, in two consecutive crop seasons . The largest proportion of photodependent N2 fixation was associated with the macrophyte Chara vulgaris in both years and at both locations . The nitrogen fixation rate associated with Chara always represented more than 45% of the global nitrogenase activity measured in the rice field . The estimated average N2 fixation rate associated with Chara was 27.53 kg of N ha–1 crop–1 . The mean estimated N2 fixation rates for the other parts of the system for all sampling periods were as follows: soil, 4.07 kg of N ha–1 crop–1; submerged parts of rice plants, 3.93 kg of N ha–1 crop–1; and roots, 0.28 kg of N ha–1 crop–1 . Micrographic studies revealed the presence of epiphytic cyanobacteria on the surface of Chara . Three-dimensional reconstructions by confocal scanning laser microscopy revealed no cyanobacterial cells inside the Chara structures . Quantification of epiphytic cyanobacteria by image analysis revealed that cyanobacteria were more abundant in nodes than in internodes (on average, cyanobacteria covered 8.4% ± 4.4% and 6.2% ± 5.0% of the surface area in the nodes and internodes, respectively) . Epiphytic cyanobacteria were also quantified by using a fluorometer . This made it possible to discriminate which algal groups were the source of chlorophyll a . Chlorophyll a measurements confirmed that cyanobacteria were more abundant in nodes than in internodes (on average, the chlorophyll a concentrations were 17.2 ± 28.0 and 4.0 ± 3.8 µg mg [dry weight] of Chara–1 in the nodes and internodes, respectively) . These results indicate that this macrophyte, which is usually considered a weed in the context of rice cultivation, may help maintain soil N fertility in the rice field ecosystem . SpiC Is Required for Translocation of Salmonella Pathogenicity Island 2 Effectors and Secretion of Translocon Proteins SseB and SseC. Jeremy A. Freeman, 2002.The Salmonella pathogenicity island 2 (SPI2) type III secretion system (TTSS) promotes Salmonella enterica serovar Typhimurium virulence for mice and increased survival and replication within eukaryotic cells . After phagocytosis, Salmonella serovar Typhimurium assembles the SPI2 TTSS to translocate over a dozen effector proteins across the phagosome membrane . SpiC has been previously shown to be a translocated effector with a large contribution to virulence (K . Uchiya, M . A . Barbieri, K . Funato, A . H . Shah, P . D . Stahl, and E . A . Groisman, EMBO J . 18:3924-3933, 1999) . This report demonstrates by competitive index that the virulence phenotype of a spiC mutant is equivalent to that of a secretion component mutant . In addition, translocation of SPI2 effector proteins was shown to require SpiC . Thus, the severe virulence phenotype resulting from deletion of spiC is likely due to the inability to translocate all SPI2 effectors . SpiC was also required to secrete translocon proteins SseB and SseC but not translocated effector SseJ, indicating that lack of assembly of the translocon explains the spiC mutant phenotype . rRNA Promoter Activity in the Fast-Growing Bacterium Vibrio natriegens. Sarah E. Aiyar, 2002.The bacterium Vibrio natriegens can double with a generation time of less than 10 min (R . G . Eagon, J . Bacteriol . 83:736-737, 1962), a growth rate that requires an extremely high rate of protein synthesis . We show here that V . natriegens' high potential for protein synthesis results from an increase in ribosome numbers with increasing growth rate, as has been found for other bacteria . We show that V . natriegens contains a large number of rRNA operons, and its rRNA promoters are extremely strong . The V . natriegens rRNA core promoters are at least as active in vitro as Escherichia coli rRNA core promoters with either E . coli RNA polymerase (RNAP) or V . natriegens RNAP, and they are activated by UP elements, as in E . coli . In addition, the E . coli transcription factor Fis activated V . natriegens rrn P1 promoters in vitro . We conclude that the high capacity for ribosome synthesis in V . natriegens results from a high capacity for rRNA transcription, and the high capacity for rRNA transcription results, at least in part, from the same factors that contribute most to high rates of rRNA transcription in E . coli, i.e., high gene dose and strong activation by UP elements and Fis . Arsenic Sensing and Resistance System in the Cyanobacterium Synechocystis sp . Strain PCC 6803. Luis López-Maury, 2003.Arsenic is one of the most important global environmental pollutants . Here we show that the cyanobacterium Synechocystis sp . strain PCC 6803 contains an arsenic and antimony resistance operon consisting of three genes: arsB, encoding a putative arsenite and antimonite carrier, arsH, encoding a protein of unknown function, and arsC, encoding a putative arsenate reductase . While arsB mutant strains were sensitive to arsenite, arsenate, and antimonite, arsC mutants were sensitive only to arsenate . The arsH mutant strain showed no obvious phenotype under the conditions tested . In vivo the arsBHC operon was derepressed by oxyanions of arsenic and antimony (oxidation state, +3) and, to a lesser extent, by bismuth (oxidation state, +3) and arsenate (oxidation state, +5) . In the absence of these effectors, the operon was repressed by a transcription repressor of the ArsR/SmtB family, encoded by an unlinked gene termed arsR . Thus, arsR null mutants showed constitutive derepression of the arsBHC operon . Expression of the arsR gene was not altered by the presence of arsenic or antimony compounds . Purified recombinant ArsR protein binds to the arsBHC promoter-operator region in the absence of metals and dissociates from the DNA in the presence of Sb(III) or As(III) but not in the presence of As(V), suggesting that trivalent metalloids are the true inducers of the system . DNase I footprinting experiments indicate that ArsR binds to two 17-bp direct repeats, with each one consisting of two inverted repeats, in the region from nucleotides -34 to + 17 of the arsBHC promoter-operator . Complex Regulation of the Bacillus subtilis Aconitase Gene. Hyun-Jin Kim, 2003.The roles of the CcpC, CodY, and AbrB proteins in regulation of the Bacillus subtilis aconitase (citB) gene were found to be distinct and to vary with the conditions and phase of growth . CcpC, a citrate-inhibited repressor that is the primary factor regulating citB expression in minimal-glucose-glutamine medium, also contributed to repression of citB during exponential-phase growth in broth medium . A null mutation in codY had no effect on citB expression during growth in minimal medium even when combined with ccpC and abrB mutations . However, a codY mutation slightly relieved repression during exponential growth in broth medium and completely derepressed citB expression when combined with a ccpC mutation . An abrB mutation led to decreased expression of citB during stationary phase in both broth and minimal medium . All three proteins bound in vitro to specific and partially overlapping sites within the citB regulatory region . Interaction of CcpC and CodY with the citB promoter region was partially competitive . Production by Clostridium acetobutylicum ATCC 824 of CelG, a Cellulosomal Glycoside Hydrolase Belonging to Family 9. Ana M. López-Contreras, 2003.The genome sequence of Clostridium acetobutylicum ATCC 824, a noncellulolytic solvent-producing strain, predicts the production of various proteins with domains typical for cellulosomal subunits . Most of the genes coding for these proteins are grouped in a cluster similar to that found in cellulolytic clostridial species, such as Clostridium cellulovorans . CAC0916, one of the open reading frames present in the putative cellulosome gene cluster, codes for CelG, a putative endoglucanase belonging to family 9, and it was cloned and overexpressed in Escherichia coli . The overproduced CelG protein was purified by making use of its high affinity for cellulose and was characterized . The biochemical properties of the purified CelG were comparable to those of other known enzymes belonging to the same family . Expression of CelG by C . acetobutylicum grown on different substrates was studied by Western blotting by using antibodies raised against the purified E . coli-produced protein . Whereas the antibodies cross-reacted with CelG-like proteins secreted by cellobiose- or cellulose-grown C . cellulovorans cultures, CelG was not detectable in extracellular medium from C . acetobutylicum grown on cellobiose or glucose . However, notably, when lichenan-grown cultures were used, several bands corresponding to CelG or CelG-like proteins were present, and there was significantly increased extracellular endoglucanase activity .
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