Fig. 1.

Quorum sensing in V. cholerae. V. cholerae QS is comprised of three systems (A). These converge at the response regulator LuxO which serves to downregulate virulence expression at high cell densities. Two external autoinducers, AI-2 (black triangles, synthesized by LuxS) and CAI-1 (black circles, synthesized by CqsA) bind to their respective sensor proteins (LuxP/LuxQ for AI-2 and CqsS for CAI-1) at high concentrations outside the cell. Autoinducer binding converts internal kinases to phosphatases and prevents the transcription of sRNAs responsible for blocking virulence inhibition. The result is the cessation of virulence gene expression at high cell densities. Arrows indicate regulation direction at low cell densities (i.e., when autoinducer is unbound). V. cholerae CAI-1 is an (S)-3-hydroxytridecan-4-one (B). OM, outer membrane; IM, inner membrane.