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Quorum Sensing Regulates Type III Secretion in Vibrio harveyi and Vibrio parahaemolyticus. Jennifer M. Henke, 2004.In a process known as quorum sensing, bacteria communicate with one another by producing, releasing, detecting, and responding to signal molecules called autoinducers . Vibrio harveyi, a marine pathogen, uses two parallel quorum-sensing circuits, each consisting of an autoinducer-sensor pair, to control the expression of genes required for bioluminescence and a number of other target genes . Genetic screens designed to discover autoinducer-regulated targets in V . harveyi have revealed genes encoding components of a putative type III secretion (TTS) system . Using transcriptional reporter fusions and TTS protein localization studies, we show that the TTS system is indeed functional in V . harveyi and that expression of the genes encoding the secretion machinery requires an intact quorum-sensing signal transduction cascade . The newly completed genome of the closely related marine bacterium Vibrio parahaemolyticus, which is a human pathogen, shows that it possesses the genes encoding both of the V . harveyi-like quorum-sensing signaling circuits and that it also has a TTS system similar to that of V . harveyi . We show that quorum sensing regulates TTS in V . parahaemolyticus . Previous reports connecting quorum sensing to TTS in enterohemorrhagic and enteropathogenic Escherichia coli show that quorum sensing activates TTS at high cell density . Surprisingly, we find that at high cell density (in the presence of autoinducers), quorum sensing represses TTS in V . harveyi and V . parahaemolyticus . Lactate-Utilizing Bacteria, Isolated from Human Feces, That Produce Butyrate as a Major Fermentation Product. Sylvia H. Duncan, 2004.The microbial community of the human colon contains many bacteria that produce lactic acid, but lactate is normally detected only at low concentrations (<5 mM) in feces from healthy individuals . It is not clear, however, which bacteria are mainly responsible for lactate utilization in the human colon . Here, bacteria able to utilize lactate and produce butyrate were identified among isolates obtained from 10–8 dilutions of fecal samples from five different subjects . Out of nine such strains identified, four were found to be related to Eubacterium hallii and two to Anaerostipes caccae, while the remaining three represent a new species within clostridial cluster XIVa based on their 16S rRNA sequences . Significant ability to utilize lactate was not detected in the butyrate-producing species Roseburia intestinalis, Eubacterium rectale, or Faecalibacterium prausnitzii . Whereas E . hallii and A . caccae strains used both D- and L-lactate, the remaining strains used only the D form . Addition of glucose to batch cultures prevented lactate utilization until the glucose became exhausted . However, when two E . hallii strains and one A . caccae strain were grown in separate cocultures with a starch-utilizing Bifidobacterium adolescentis isolate, with starch as the carbohydrate energy source, the L-lactate produced by B . adolescentis became undetectable and butyrate was formed . Such cross-feeding may help to explain the reported butyrogenic effect of certain dietary substrates, including resistant starch . The abundance of E . hallii in particular in the colonic ecosystem suggests that these bacteria play important roles in preventing lactate accumulation . Isolation and Characterization of BTF-37: Chromosomal DNA Captured from Bacteroides fragilis That Confers Self-Transferability and Expresses a Pilus-Like Structure in Bacteroides spp . and Escherichia coli. Gayatri Vedantam, 2002.We report the isolation and preliminary characterization of BTF-37, a new 52-kb transfer factor isolated from Bacteroides fragilis clinical isolate LV23 . BTF-37 was obtained by the capture of new DNA in the nonmobilizable Bacteroides-Escherichia coli shuttle vector pGAT400  BglII using a functional assay . BTF-37 is self-transferable within and from Bacteroides and also self-transfers in E . coli . Partial DNA sequencing, colony hybridization, and PCR revealed the presence of Tet element-specific sequences in BTF-37 . In addition, Tn5520, a small mobilizable transposon that we described previously (G . Vedantam, T . J . Novicki, and D . W . Hecht, J . Bacteriol . 181:2564–2571, 1999), was also coisolated within BTF-37 . Scanning and transmission electron microscopy of Tet element-containing Bacteroides spp . and BTF-37-harboring Bacteroides and E . coli strains revealed the presence of pilus-like cell surface structures . These structures were visualized in Bacteroides spp . only when BTF-37 and Tet element strains were induced with subinhibitory concentrations of tetracycline and resembled those encoded by E . coli broad-host-range plasmids . We conclude that we have captured a new, self-transferable transfer factor from B . fragilis LV23 and that this new factor encodes a tetracycline-inducible Bacteroides sp . conjugation apparatus .
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