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The O-Antigen Gene Cluster of Escherichia coli O55:H7 and Identification of a New UDP-GlcNAc C4 Epimerase Gene. Lei Wang, 2002.Escherichia coli O55 is an important antigen which is often associated with enteropathogenic E . coli clones . We sequenced the genes responsible for its synthesis and identified genes for O-antigen polymerase, O-antigen flippase, four enzymes involved in GDP-colitose synthesis, and three glycosyltransferases, all by comparison with known genes . Upstream of the normal O-antigen region there is a gne gene, which encodes a UDP-GlcNAc epimerase for converting UDP-GlcNAc to UDP-GalNAc and is essential for O55 antigen synthesis . The O55 gne product has only 20 and 26% identity to the gne genes of Pseudomonas aeruginosa and E . coli O113, respectively . We also found evidence for the O55 gene cluster's having evolved from another gene cluster by gain and loss of genes . Only three of the GDP-colitose pathway genes are in the usual location, the other two being separated, although nearby . It is thought that the E . coli O157:H7 clone evolved from the O55:H7 clone in part by transfer of the O157 gene cluster into an O55 lineage . Comparison of genes flanking the O-antigen gene clusters of the O55:H7 and O157:H7 clones revealed one recombination site within the galF gene and located the other between the hisG and amn genes . Genes outside the recombination sites are 99.6 to 100% identical in the two clones, while most genes thought to have transferred with the O157 gene cluster are 95 to 98% identical . Lateral Flagella and Swarming Motility in Aeromonas Species. Sylvia M. Kirov, 2002.Swarming motility, a flagellum-dependent behavior that allows bacteria to move over solid surfaces, has been implicated in biofilm formation and bacterial virulence . In this study, light and electron microscopic analyses and genetic and functional investigations have shown that at least 50% of Aeromonas isolates from the species most commonly associated with diarrheal illness produce lateral flagella which mediate swarming motility . Aeromonas lateral flagella were optimally produced when bacteria were grown on solid medium for  8 h . Transmission and thin-section electron microscopy confirmed that these flagella do not possess a sheath structure . Southern analysis of Aeromonas reference strains and strains of mesophilic species (n = 84, varied sources and geographic regions) with a probe designed to detect lateral flagellin genes (lafA1 and lafA2) showed there was no marked species association of laf distribution . Approximately 50% of these strains hybridized strongly with the probe, in good agreement with the expression studies . We established a reproducible swarming assay (0.5% Eiken agar in Difco broth, 30°C) for Aeromonas spp . The laf-positive strains exhibited vigorous swarming motility, whereas laf-negative strains grew but showed no movement from the inoculation site . Light and scanning electron microscopic investigations revealed that lateral flagella formed bacterium-bacterium linkages on the agar surface . Strains of an Aeromonas caviae isolate in which lateral flagellum expression was abrogated by specific mutations in flagellar genes did not swarm, proving conclusively that lateral flagella are required for the surface movement . Whether lateral flagella and swarming motility contribute to Aeromonas intestinal colonization and virulence remains to be determined .
Thanks, Charley. Michael D. Manson, 2002. Global Regulation of Staphylococcus aureus Genes by Rot. B. Saïd-Salim, 2003.Staphylococcus aureus produces a wide array of cell surface and extracellular proteins involved in virulence . Expression of these virulence factors is tightly controlled by numerous regulatory loci, including agr, sar, sigB, sae, and arl, as well as by a number of proteins with homology to SarA . Rot (repressor of toxins), a SarA homologue, was previously identified in a library of transposon-induced mutants created in an agr-negative strain by screening for restored protease and alpha-toxin . To date, all of the SarA homologues have been shown to act as global regulators of virulence genes . Therefore, we investigated the extent of transcriptional regulation of staphylococcal genes by Rot . We compared the transcriptional profile of a rot agr double mutant to that of its agr parental strain by using custom-made Affymetrix GeneChips . Our findings indicate that Rot is not only a repressor but a global regulator with both positive and negative effects on the expression of S . aureus genes . Our data also indicate that Rot and agr have opposing effects on select target genes . These results provide further insight into the role of Rot in the regulatory cascade of S . aureus virulence gene expression .
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