Fig. 8.

Quorum-sensing control in V. parahaemolyticus. The strains analyzed in this work support the general Vibrio model of the quorum-sensing pathway for information flow in V. parahaemolyticus. Low cell density can be mimicked by a constitutively active LuxO* or ΔopaR strains; high cell density is mimicked by ΔluxO. The constitutive form of LuxO results in elevated expression of at least three small RNAs (Qrrs). Functioning as the downstream regulator in the pathway, opaR is epistatic to luxO. Transcriptome analyses reveal that OpaR regulates ∼210 genes negatively and 113 genes positively (>4-fold). The selected subset of regulated genes shown in the model include those for which we have experimental evidence or those displaying very high degrees of regulation in the array analyses (i.e., 10-fold or greater changes in gene expression). Previous work showed that OpaR represses swarming and induces capsular polysaccharide gene expression; here we demonstrate that OpaR regulates the level of c-di-GMP in the cell, represses cytotoxicity for host cells in coculture, and induces competence for DNA uptake. Motility and/or virulence may drive selection toward strains in the quorum-silenced state, either via loss of function of the output regulator OpaR or via altered function of the quorum regulator LuxO.