Quorum sensing is a cell‑density‑dependent communication process used by bacteria and some archaea to coordinate collective behaviour through the production and detection of small signalling molecules.
Explanation
In quorum sensing, individual cells produce autoinducers that diffuse into the environment. As a bacterial population grows, the concentration of autoinducer increases. When it surpasses a threshold, these molecules bind to specific receptors and trigger changes in gene expression across the community. Gram‑negative bacteria typically use N‑acyl homoserine lactones (AHLs) that interact with LuxR‑type transcription factors, while Gram‑positive species secrete modified oligopeptides that are detected by two‑component sensor kinases. A third class of signals, known as autoinducer‑2, facilitates interspecies communication. Quorum sensing regulates diverse functions including bioluminescence, biofilm formation, sporulation, virulence factor production and secondary metabolite synthesis. By acting collectively, bacteria can optimise resource use, evade host defences and adapt to environmental changes. Disruption of signalling, termed quorum quenching, is being explored as a strategy to control infections by preventing coordinated pathogenic behaviours.
Mechanisms and Examples
The marine bacterium Vibrio fischeri uses quorum sensing to regulate luminescence in symbiosis with the Hawaiian bobtail squid. Only when the population within the light organ is dense enough does the lux operon activate light production. Pseudomonas aeruginosa employs multiple AHL circuits to control biofilm formation and the secretion of elastase and other virulence factors during opportunistic infections. In Staphylococcus aureus, the agr system uses autoinducing peptides to coordinate toxin production and biofilm dispersal. Vibrio harveyi produces both species‑specific and interspecies signals, highlighting the complexity of bacterial communication networks. These examples demonstrate how quorum sensing enables microbes to behave as coordinated multicellular systems.
Quorum sensing is a fundamental mechanism of microbial communication that allows populations to sense their numbers and regulate group behaviour. Understanding and manipulating these signalling pathways could yield novel approaches to control pathogenicity and harness beneficial microbial activities.
Related Terms: Autoinducer, Biofilm, Signal transduction, Bacterial communication, Virulence factor