Figure 1.

The quorum-sensing circuit and growth of a colony of V. harveyi. (A) Wild-type V. harveyi uses three autoinducers (AIs) to gauge the population density as well as the species composition of the vicinal community. The AIs are AI-1, an intraspecies signal; CAI-1, an intragenera signal; and AI-2, an interspecies signal. In V. harveyi, detection of AI-1, CAI-1, and AI-2 involves the transmembrane receptors LuxN, CqsS, and LuxPQ, respectively. Black arrows denote the direction of phosphate flow when the concentration of AIs is low. In the absence of AIs (low cell density), the receptors are kinases that funnel phosphate through a shared pathway that ultimately represses translation of the mRNA encoding the master quorum-sensing regulator, LuxR. In response to AIs (i.e., at high cell density), the receptors convert from being kinases to being phosphatases. Phosphate is drained from the signaling pathway, which relieves repression of luxR mRNA translation. (B) In the V. harveyi strain used here, only exogenously added AI-1 and AI-2 are detected (by the sensors LuxN and LuxPQ, respectively), which ultimately controls production of the master regulator LuxR (here labeled with mCherry). (C) Sequence of fluorescent images (red) overlaid with simultaneous phase images (gray) showing the growth of V. harveyi cells containing LuxR-mCherry.