"Quorum sensing-controlled behaviors are those that only occur when bacteria are at high cell population densities. These behaviors are ones that are unproductive when undertaken by an individual bacterium but become effective by the simultaneous action of a group of cells. For example, quorum sensing regulates bioluminescence, virulence factor expression, biofilm formation, sporulation, and mating. Quorum sensing is achieved through the production, release, and subsequent detection of and response to threshold concentrations of signal molecules called autoinducers. The accumulation of a stimulatory concentration of an extracellular autoinducer can only occur when a sufficient number of cells, a “quorum,” is present."