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The PhoP-PhoQ Two-Component Regulatory System of Photorhabdus luminescens Is Essential for Virulence in Insects. Sylviane Derzelle, 2004.Photorhabdus luminescens is a symbiont of entomopathogenic nematodes. Analysis of the genome sequence of this organism revealed a homologue of PhoP-PhoQ, a two-component system associated with virulence in intracellular bacterial pathogens . This organismwas shown to respond to the availability of environmental magnesium.A mutant with a knockout mutation in the regulatory componentof this system [phoP] had no obvious growth defect . It was,however, more motile and more sensitive to antimicrobial peptidesthan its wild-type parent . Remarkably, the mutation eliminatedvirulence in an insect model . No insect mortality was observedafter injection of a large number of the phoP bacteria, whilevery small amounts of parental cells killed insect larvae inless than 48 h . At the molecular level, the PhoPQ system mediatedMg2+-dependent modifications in lipopolysaccharides and controlleda locus [pbgPE] required for incorporation of 4-aminoarabinoseinto lipid A . Mg2+-regulated gene expression of pbgP1 was absentin the mutant and was restored when phoPQ was complemented intrans . This finding highlights the essential role played byPhoPQ in the virulence of an entomopathogen. Enhancement of the Enterocin CRL35 Activity by a Synthetic Peptide Derived from the NH2-Terminal Sequence. Lucila Saavedra, 2004.The enterocin CRL35 biosynthetic gene cluster was cloned and sequenced . The sequence was revealed to be highly identical to that of the mundticin KS gene cluster (S . Kawamoto, J . Shima, R . Sato, T . Eguchi, S . Ohmomo, J . Shibato, N . Horikoshi, K . Takeshita, and T . Sameshima, Appl . Environ . Microbiol . 68:3830-3840, 2002) . Short synthetic peptides were designed based on the bacteriocin sequence and were evaluated in antimicrobial competitive assays . The peptide KYYGNGVSCNKKGCS produced an enhancement of enterocin CRL35 antimicrobial activity in a buffer system . Behavior of Sister Copies of Mini-F Plasmid after Synchronized Plasmid Replication in Escherichia coli Cells. Toshinari Onogi, 2002.To clarify whether sister copies of mini-F plasmid are immediately separated from each other after replication, we analyzed the behavior of sister mini-F copies after synchronized replication of mini-F . Sister copies of mini-F were separated immediately or shortly after replication, in contrast to sister oriC copies of the Escherichia coli chromosome . Global Role for ClpP-Containing Proteases in Stationary-Phase Adaptation of Escherichia coli. Dieter Weichart, 2003.To elucidate the involvement of proteolysis in the regulation of stationary-phase adaptation, the clpA, clpX, and clpP protease mutants of Escherichia coli were subjected to proteome analysis during growth and during carbon starvation . For most of the growth-phase-regulated proteins detected on our gels, the clpA, clpX, or clpP mutant failed to mount the growth-phase regulation found in the wild type . For example, in the clpP and clpA mutant cultures, the Dps protein, the WrbA protein, and the periplasmic lysine-arginine-ornithine binding protein ArgT did not display the induction typical for late-stationary-phase wild-type cells . On the other hand, in the protease mutants, a number of proteins accumulated to a higher degree than in the wild type, especially in late stationary phase . The proteins affected in this manner include the LeuA, TrxB, GdhA, GlnA, and MetK proteins and alkyl hydroperoxide reductase (AhpC) . These proteins may be directly degraded by ClpAP or ClpXP, respectively, or their expression could be modulated by a protease-dependent mechanism . From our data we conclude that the levels of most major growth-phase-regulated proteins in E . coli are at some point controlled by the activity of at least one of the ClpP, ClpA, and ClpX proteins . Cultures of the strains lacking functional ClpP or ClpX also displayed a more rapid loss of viability during extended stationary phase than the wild type . Therefore, regulation by proteolysis seems to be more important, especially in resting cells, than previously suspected . Mutations in Haemophilus influenzae Mismatch Repair Genes Increase Mutation Rates of Dinucleotide Repeat Tracts but Not Dinucleotide Repeat-Driven Pilin Phase Variation Rates. Christopher D. Bayliss, 2004.High-frequency, reversible switches in expression of surface antigens, referred to as phase variation (PV), are characteristic of Haemophilus influenzae . PV enables this bacterial species, an obligate commensal and pathogen of the human upper respiratory tract, to adapt to changes in the host environment . Phase-variable hemagglutinating pili are expressed by many H . influenzae isolates . PV involves alterations in the number of 5' TA repeats located between the –10 and –35 promoter elements of the overlapping, divergently orientated promoters of hifA and hifBCDE, whose products mediate biosynthesis and assembly of pili . Dinucleotide repeat tracts are destabilized by mismatch repair (MMR) mutations in Escherichia coli . The influence of mutations in MMR genes of H . influenzae strain Rd on dinucleotide repeat-mediated PV rates was investigated by using reporter constructs containing 20 5' AT repeats . Mutations in mutS, mutL, and mutH elevated rates approximately 30-fold, while rates in dam and uvrD mutants were increased 14- and 3-fold, respectively . PV rates of constructs containing 10 to 12 5' AT repeats were significantly elevated in mutS mutants of H . influenzae strains Rd and Eagan . An intact hif locus was found in 14 and 12% of representative nontypeable H . influenzae isolates associated with either otitis media or carriage, respectively . Nine or more tandem 5' TA repeats were present in the promoter region . Surprisingly, inactivation of mutS in two serotype b H . influenzae strains did not alter pilin PV rates . Thus, although functionally analogous to the E . coli MMR pathway and active on dinucleotide repeat tracts, defects in H . influenzae MMR do not affect 5' TA-mediated pilin PV . Spatial Distribution of Rhodopseudomonas palustris Ecotypes on a Local Scale. S. J. Bent, 2003.The number, spatial distribution, and significance of genetically distinguishable ecotypes of prokaryotes in the environment are poorly understood . Oda et al . (Y . Oda, B . Star, L . A . Huisman, J . C . Gottschal, and L . J . Forney, Appl . Environ . Microbiol . 69:xxx-xxx, 2003) have shown that Rhodopseudomonas palustris ecotypes were lognormally distributed along a 10-m transect and that multiple strains of the species could coexist in 0.5-g sediment samples . To extend these observations, we investigated the clonal diversity of R . palustris in 0.5-g samples taken from the corners and center of a 1-m square . A total of 35 or 36 clones were recovered by direct plating from each sample and were characterized by BOX A1R repetitive element-PCR genomic DNA fingerprinting . Isolates with fingerprint images that were  80% similar to each other were defined as the same genotype . Among the 178 isolates studied, 32 genotypes were identified, and each genotype contained between 1 and 40 isolates . These clusters were consistent with minor variations found in 16S rRNA gene sequences . The Shannon indices of the genotypic diversity within each location ranged from 1.08 (5 genotypes) to 2.18 (13 genotypes) . Comparison of the rank abundance of genotypes found in pairs of locations showed that strains from three locations were similar to each other, with Morisita-Horn similarity coefficients ranging from 0.59 to 0.71 . All comparisons involving the remaining two locations resulted in coefficients between 0 and 0.12 . From these results we inferred that the patterns of ecotype diversity at the sampling site are patchy at a 1-m scale and postulated that factors such as mixing, competitive interactions, and microhabitat variability are likely to be responsible for the maintenance of the similarities between some locations and the differences between others .
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