Figure 4.
Quorum sensing. (A) Example of communication molecules of three classes. AHLs are found in Gram-negative bacteria such as V. fischeri. AIPs are produced by Gram-positive strains like Staphylococcus. AI-2 is an intermediate of methionine metabolism, found among both Gram-positive and Gram-negative bacteria. (B) QS bacteria produce signal molecules at a basal level that accumulate locally. Signal levels reflect the local population density and trigger a collective response at high densities. Responding cells are indicated in orange. (C) The QS response is often nonlinear with signal concentration. Typically, response levels increase sharply above a critical signal threshold.
