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Induction of Plantaricin Production in Lactobacillus plantarum NC8 after Coculture with Specific Gram-Positive Bacteria Is Mediated by an Autoinduction Mechanism. Antonio Maldonado, 2004.Plantaricin NC8 [PLNC8], a coculture-inducible two-peptide bacteriocin from Lactobacillus plantarum NC8, has recently been purified and genetically characterized . Analysis of an 8.1-kb NC8 DNA region downstream of the PLNC8 operon revealed the presenceof at least four operons involved in bacteriocin production,showing high homology to the plantaricin cluster in L . plantarumC11 . However, we found a three-component regulatory operon involvinga quorum-sensing mechanism . Two of these components, the induction factor [PLNC8IF] and the histidine kinase, are novel, whilethe response regulator is identical to PlnD from C11 . Homologous expression of plNC8IF in NC8 allowed constitutive bacteriocin production . Heterologous expression of this gene in Lactococcus lactis MG1363 produced supernatants which promoted bacteriocin production in NC8 . Reverse transcription-PCR studies indicatedthat cocultivation of NC8 with inducing cells promoted transcriptionof the bacteriocin and regulatory operons in NC8 . An identicalresult was obtained after addition of an external source ofPLNC8IF . We propose that the presence of specific bacteria couldact as an environmental signal that is able to switch on bacteriocinproduction in L . plantarum NC8 via a quorum-sensing mechanismmediated by PLNC8IF. Genes Regulated by TorR, the Trimethylamine Oxide Response Regulator of Shewanella oneidensis. Christophe Bordi, 2004.The torECAD operon encoding the trimethylamine oxide (TMAO) respiratory system of Shewanella oneidensis is positively controlled by the TorS/TorR two-component system when TMAO is available . Activation of the tor operon occurs upon binding of the phosphorylated response regulator TorR to a single operator site containing the direct repeat nucleotide sequence TTCATAN4TTCATA . Here we show that the replacement of any nucleotide of one TTCATA hexamer prevented TorR binding in vitro, meaning that TorR specifically interacts with this DNA target . Identical direct repeat sequences were found in the promoter regions of torR and of the new gene torF (SO4694), and they allowed TorR binding to both promoters . Real-time PCR experiments revealed that torR is negatively autoregulated, whereas torF is strongly induced by TorR in response to TMAO . Transcription start site location and footprinting analysis indicate that the operator site at torR overlaps the promoter –10 box, whereas the operator site at torF is centered at –74 bp from the start site, in agreement with the opposite role of TorR in the regulation of the two genes . Since torF and torECAD are positively coregulated by TorR, we propose that the TorF protein plays a role related to TMAO respiration . Arsenite Oxidase aox Genes from a Metal-Resistant ß-Proteobacterium. Daniel Muller, 2003.The ß-proteobacterial strain ULPAs1, isolated from an arsenic-contaminated environment, is able to efficiently oxidize arsenite [As(III)] to arsenate [As(V)] . Mutagenesis with a lacZ-based reporter transposon yielded two knockout derivatives deficient in arsenite oxidation . Sequence analysis of the DNA flanking the transposon insertions in the two mutants identified two adjacent open reading frames, named aoxA and aoxB, as well as a putative promoter upstream of the aoxA gene . Reverse transcription-PCR data indicated that these genes are organized in an operonic structure . The proteins encoded by aoxA and aoxB share 64 and 72% identity with the small Rieske subunit and the large subunit of the purified and crystallized arsenite oxidase of Alcaligenes faecalis, respectively (P . J . Ellis, T . Conrads, R . Hille, and P . Kuhn, Structure [Cambridge] 9:125-132, 2001) . Importantly, almost all amino acids involved in cofactor interactions in both subunits of the A . faecalis enzyme were conserved in the corresponding sequences of strain ULPAs1 . An additional Tat (twin-arginine translocation) signal peptide sequence was detected at the N terminus of the protein encoded by aoxA, strongly suggesting that the Tat pathway is involved in the translocation of the arsenite oxidase to its known periplasmic location . Release of Extracellular Transformable Plasmid DNA from Escherichia coli Cocultivated with Algae. Kazuaki Matsui, 2003.We studied the effects of cocultivation with either Euglena gracilis (Euglenophyta), Microcystis aeruginosa (Cyanophyta), Chlamydomonas neglecta (Chlorophyta), or Carteria inversa (Chlorophyta) on the production of extracellular plasmid DNA by Escherichia coli LE392(pKZ105) . Dot blot hybridization analysis showed a significant release of plasmid DNA by cocultivation with all the algae tested . Further analysis by electrotransformation confirmed the release of transformable plasmid DNA by cocultivation with either E . gracilis, M . aeruginosa, or C . inversa . These results suggest algal involvement in bacterial horizontal gene transfer by stimulating the release of transformable DNA into aquatic environments .
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