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Recombination in the Genome of Chlamydia trachomatis Involving the Polymorphic Membrane Protein C Gene Relative to ompA and Evidence for Horizontal Gene Transfer. Joćo P. Gomes, 2004.Genome sequencing of Chlamydia trachomatis serovar D has identified polymorphic membrane proteins (Pmp) that are a newly recognized protein family unique to the Chlamydiaceae family . Cumulative data suggest that these diverse proteins are expressed on the cell surface and might be immunologically important . We performed phylogenetic analyses and statistical modeling with 18 reference serovars and 1 genovariant of C . trachomatis to examine the evolutionary characteristics and comparative genetics of PmpC and pmpC, the gene that encodes this protein . We also examined 12 recently isolated ocular and urogenital clinical samples, since reference serovars are laboratory adapted and may not represent strains that are presently responsible for human disease . Phylogenetic reconstructions revealed a clear distinction for disease groups, corresponding to levels of tissue specificity and virulence of the organism . Further, the most prevalent serovars, E, F, and Da, formed a distinct clade . According to the results of comparative genetic analyses, these three genital serovars contained two putative insertion sequence (IS)-like elements with 10- and 15-bp direct repeats, respectively, while all other genital serovars contained one IS-like element . Ocular trachoma serovars also contained both insertions . Previously, no IS-like elements have been identified for Chlamydiaceae . Surprisingly, 7 (58%) of 12 clinical isolates revealed pmpC sequences that were identical to the sequences of other serovars, providing clear evidence for a high rate of whole-gene recombination . Recombination and the differential presence of IS-like elements among distinct disease and prevalence groups may contribute to genome plasticity, which may lead to adaptive changes in tissue tropism and pathogenesis over the course of the organism's evolution . Solar and Temporal Effects on Escherichia coli Concentration at a Lake Michigan Swimming Beach. Richard L. Whitman, 2004.Studies on solar inactivation of Escherichia coli in freshwater and in situ have been limited . At 63rd St . Beach, Chicago, Ill., factors influencing the daily periodicity of culturable E . coli, particularly insolation, were examined . Water samples for E . coli analysis were collected twice daily between April and September 2000 three times a week along five transects in two depths of water . Hydrometeorological conditions were continuously logged: UV radiation, total insolation, wind speed and direction, wave height, and relative lake level . On 10 days, transects were sampled hourly from 0700 to 1500 h . The effect of sunlight on E . coli inactivation was evaluated with dark and transparent in situ mesocosms and ambient lake water . For the study, the number of E . coli samples collected (n) was 2,676 . During sunny days, E . coli counts decreased exponentially with day length and exposure to insolation, but on cloudy days, E . coli inactivation was diminished; the E . coli decay rate was strongly influenced by initial concentration . In situ experiments confirmed that insolation primarily inactivated E . coli; UV radiation only marginally affected E . coli concentration . The relationship between insolation and E . coli density is complicated by relative lake level, wave height, and turbidity, all of which are often products of wind vector . Continuous importation and nighttime replenishment of E . coli were evident . These findings (i) suggest that solar inactivation is an important mechanism for natural reduction of indicator bacteria in large freshwater bodies and (ii) have implications for management strategies of nontidal waters and the use of E . coli as an indicator organism . Determinants of the Src Homology Domain 3-Like Fold. J. Alejandro D'Aquino, 2003.In eukaryotes, the Src homology domain 3 (SH3) is a very important motif in signal transduction . SH3 domains recognize poly-proline-rich peptides and are involved in protein-protein interactions . Until now, the existence of SH3 domains has not been demonstrated in prokaryotes . However, the structure of the C-terminal domain of DtxR clearly shows that the fold of this domain is very similar to that of the SH3 domain . In addition, there is evidence that the C-terminal domain of DtxR binds to poly-proline-rich regions . Other bacterial proteins have domains that are structurally similar to the SH3 domain but whose functions are unknown or differ from that of the SH3 domain . The observed similarities between the structures of the C-terminal domain of DtxR and the SH3 domain constitute a perfect system to gain insight into their function and information about their evolution . Our results show that the C-terminal domain of DtxR shares a number of conserved key hydrophobic positions not recognizable from sequence comparison that might be responsible for the integrity of the SH3-like fold . Structural alignment of an ensemble of such domains from unrelated proteins shows a common structural core that seems to be conserved despite the lack of sequence similarity . This core constitutes the minimal requirements of protein architecture for the SH3-like fold . Development of a Physical and Genetic Map of the Virulent Wolbachia Strain wMelPop. Ling V. Sun, 2003.We report here the construction of a physical and genetic map of the virulent Wolbachia strain, wMelPop . This map was determined by ordering 28 chromosome fragments that resulted from digestion with the restriction endonucleases FseI, ApaI, SmaI, and AscI and were resolved by pulsed-field gel electrophoresis . Southern hybridization was done with 53 Wolbachia-specific genes as probes in order to determine the relative positions of these restriction fragments and use them to serve as markers . Comparison of the resulting map with the whole genome sequence of the closely related benign Wolbachia strain, wMel, shows that the two genomes are largely conserved in gene organization with the exception of a single inversion in the chromosome . An Improved Cloning Vector for Construction of Gene Replacements in Listeria monocytogenes. Guojie Li, 2003.Listeria monocytogenes is a gram-positive, facultative intracellular bacterium implicated in severe food-borne illness (listeriosis) in humans . The construction of well-defined gene replacements in the genome of L . monocytogenes has been instrumental to several genetic studies of the virulence and other attributes of the organism . Construction of such mutations by currently available procedures, however, tends to be labor intensive, and gene replacement mutants are sometimes difficult to recover due to lack of direct selection for the construct . In this study we describe the construction and use of plasmid vector pGF-EM, which can be conjugatively transferred from Escherichia coli S17-1 to L . monocytogenes and which provides the genetic means for direct selection of gene replacements .
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