Quorum Sensing
Outstanding scientist and doctor of sciences on the topic “Quorum Sensing”. Quorum sensing (QS) is a mechanism of communication used by bacteria to coordinate their gene expression in response to changes in cell-population density. By detecting and responding to changes in the population density of other cells, bacteria can optimize their behavior for maximum benefit. For example, QS allows bacteria to synchronize their activities so that they can more effectively carry out tasks such as virulence factor production or antibiotic resistance. In addition, QS enables bacteria to regulate their metabolism and physiology in response to changes in their environment, such as the availability of nutrients or the presence of stressors.
The ability of bacteria to sense and respond to changes in cell-population density is mediated by specialised proteins known as autoinducers (AIs). AIs are small molecules that are produced by bacterial cells and secreted into the environment. Once secreted, AIs diffusively interact with nearby cells, where they bind to specific receptors and trigger a change in gene expression. The concentration of AIs within a given environment provides a means for bacteria to monitor local cell-population density. When the AI concentration reaches a certain threshold – known as the quorum threshold – it triggers a change in gene expression that allows bacteria to coordinately regulate their activities.
There are two main types of quorum sensing: LuxR-type quorum sensing and AraC-type quorum sensing. LuxR-type quorum sensing uses an AI called AHL (acyl homoserine lactone) while AraC-type quorum sensing uses an AI called HSL (homoserine lactone). AHLs are produced by many different species of Gram-negative bacteria, while HSLs are produced by both Gram-negative and Gram-positive bacteria. Both AHLs and HSLs can diffuse freely through cellular membranes, allowing them to interact with nearby cells regardless of species identity. This makes LuxR-type and AraC-type quorumsensing ideal for interspecies communication within mixed microbial communities.
LuxR-type quorum sensing was first described in the bacterium Vibrio harveyi, which uses AHLs for intraspecies communication . Subsequent studies have shown that LuxR type systems are widespread among Gram – negative bacteria including Pseudomonas aeruginosa , Burkholderia cenocepacia , Bordetella pertussis and Yersinia enterocolitica . Studies on these pathogens have revealed that LuxR – type systems play important roles in regulating virulence factor production , biofilm formation motility antibiotic resistance and other processes . In contrast , very little is known about how AraC – type systems function within bacterial cells . However , recent studies have begun to shed light on this subject . For example , one study showed that an AraC – type system regulates flagellar synthesis indicating that this system may be involved in controlling motility . Another study found that an AraC – type system influences biofilm formation suggesting a role for this system in regulating surface attachment . Collectively , these studies suggest that both LuxR – type and AraC – type systems play important roles in controlling various aspects of bacterial physiology .