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.