From motility to virulence: Sensing and responding to environmental signals in Vibrio cholerae.

Sensing its changing environment is key for Vibrio cholerae when making the transition from an aquatic lifestyle to one more suited to a human host. An inverse correlation between motility and virulence gene expression has been reported, with the NADH : ubiquinone oxidoreductase system which powers motility by generating a sodium-motive force, playing a pivotal role. Recent studies have demonstrated that bile inhibits activity of the transcription factor ToxT, a protein responsible for direct activation of numerous virulence gene promoters. In addition, recent technological advances have allowed for the analysis of in-vivo-induced genes and assessment of their timing of expression. Use of recombinase-based in vivo expression technology has revealed that the toxin-coregulated pilus (a colonization factor) is expressed before cholera toxin. Components of an acid-tolerance response system have also been found using this method as well as signature-tagged mutagenesis. Finally, a role for quorum sensing in regulation of virulence gene expression has recently been established.