quorum sensing

quorum sensing

a phenomenon in bacteria that limits certain behaviors to occurring only above a certain population density.

quorum sensing

n.

A phenomenon in which a population of bacteria produces and responds to intercellular chemical signals whose concentration indicates the density of the population. When the density reaches a certain level, genes are expressed that allow for coordinated group behavior, as in bioluminescence or the formation of biofilms.

quo·rum sens·ing

(kwōr'ŭm sens'ing)

A process whereby bacteria communicate by means of extracellular molecules called pheromones.

quorum sensing

a process in which unicellular organisms secrete signal molecules that influence the behaviour of a population of identical organisms, but only when the density (number of cells per unit volume) of that population is above a certain level. Cells sense the concentration of the secreted signal molecule, often a homoserine lactone, which tells them how many other cells are in their environment. When a threshold concentration of the signal molecule is reached, the population density has achieved a critical level or quorum, and quorum-dependent genes are expressed by auto induction. A given species can produce a range of autoinducer signal molecules, which regulate expression of genes governing characteristics that are only exhibited above this critical population density Thus specific characteristics may be displayed by cells present at high density, but not by the same cells when present at low density Examples of quorum sensing include, bioluminescence of Photobacterium fischeri when occurring as a SYMBIONT in high density populations, but not when free-living in low density populations; promotion of COMPETENCE for TRANSFORMATION in Bacillus subtilis, when present at high density; and production of VIRULENCE factors in Pseudomonas aeruginosa.