ABSTRACTVibrio choleraeis naturally competent when grown on chitin. It is known that expression of the major regulator of competence, TfoX, is controlled by chitin; however, the molecular mechanisms underlying this requirement for chitin have remained unclear. In the present study, we identify and characterize a membrane-bound transcriptional regulator that positively regulates the small RNA (sRNA) TfoR, which posttranscriptionally enhancestfoXtranslation. We show that this regulation of thetfoRpromoter is direct by performing electrophoretic mobility shift assays and by heterologous expression of this system inEscherichia coli. This transcriptional regulator was recently identified independently and was named “TfoS” (S. Yamamoto et al., Mol. Microbiol., in press, doi:10.1111/mmi.12462). Using a constitutively active form of TfoS, we demonstrate that the activity of this regulator is sufficient to promote competence inV. choleraein the absence of chitin. Also, TfoS contains a large periplasmic domain, which we hypothesized interacts with chitin to regulate TfoS activity. In the heterologous hostE. coli, we demonstrate that chitin oligosaccharides are sufficient to activate TfoS activity at thetfoRpromoter. Collectively, these data characterize TfoS as a novel chitin-sensing transcriptional regulator that represents the direct link between chitin and natural competence inV. cholerae.IMPORTANCENaturally competent bacteria can take up exogenous DNA from the environment and integrate it into their genome by homologous recombination. This ability to take up exogenous DNA is shared by diverse bacterial species and serves as a mechanism to acquire new genes to enhance the fitness of the organism. Several members of the familyVibrionaceaebecome naturally competent when grown on chitin; however, a molecular understanding of how chitin activates competence is lacking. Here, we identify a novel membrane-bound transcriptional regulator that is required for natural transformation in the human pathogenVibrio cholerae. We demonstrate that this regulator senses chitin oligosaccharides to activate the competence cascade, thus, uncovering the molecular link between chitin and natural competence in thisVibriospecies.
Implication of Cholesterol in Regulating the Membrane-Interaction Mechanism of Vibrio cholerae Cytolysin, a Beta-Barrel Pore-Forming Toxin
