Figure 4.

QS in V. cholerae. Two QS signals AI-2 and CAI-1 work synergistically to regulate virulence factor expression and biofilm development. At low population density in the absence of signal molecules, the absence of HapR triggers the expression of genes such as vps, ctx and tcp, which are normally repressed by HapR. As the cell density and therefore the signal molecule concentration increases HapR represses the expression of the genes responsible for colonization and promotes detachment from the intestinal epithelium to enable the organism to exit the host (adapted from Kaper & Sperandio 2005).