In biology, quorum sensing is a system of stimuli and response correlated to population density. In addition to its function in biological systems, quorum sensing has several useful applications for computing quorum sensing in bacteria pdf robotics. Some of the best-known examples of quorum sensing come from studies of bacteria.
Bacteria use quorum sensing to regulate certain phenotype expressions, which in turn, coordinate their behaviours. Quorum sensing functions based on the local density of the bacterial population in the immediate environment. It can occur within a single bacterial species, as well as between diverse species. In order for the bacteria to use quorum sensing constitutively, they must possess three characteristics: to secrete a signaling molecule, an autoinducer, to detect the change in concentration of signaling molecules, and to regulate gene transcription as a response. When gram-positive bacteria detect high concentration of AIP in the environment, AIP bind to a receptor to activate kinase. The kinase phosphorylates a transcription factor, which regulated gene transcription. This is called a two-component system.
Another possible mechanism is that AIP is transported into the cytosol, and binds directly to a transcription factor to initiate or inhibit transcription. Usually AHLs do not need additional processing, and bind directly to transcription factors to regulate gene expression. Some gram-negative bacteria may use the two-component system as well. This species uses AI-2, which is produced and processed by the lsr operon. Salmonella enterica do not produce AHL signals commonly found in other Gram-negative bacteria.
However, they have a receptor that detects AHLs from other bacteria and change their gene expression in accordance with the presence of other “quorate” populations of Gram-negative bacteria. Salmonella encodes a LuxR homolog, SdiA, but does not encode an AHL synthase. SdiA detects AHLs produced by other species of bacteria including Aeromonas hydrophila, Hafnia alvei, and Yersinia enterocolitica. The opportunistic pathogen Pseudomonas aeruginosa uses quorum sensing to coordinate the formation of biofilms, swarming motility, exopolysaccharide production, virulence, and cell aggregation. It has recently been found that Acinetobacter sp.
This bacterium, an emerging pathogen, produces AHLs. It produces AHLs and also, it can degrade the AHL molecules as well. This bacterium was previously considered a fish pathogen, but it has recently emerged as a human pathogen. The YenR and YenI proteins produced by the gammaproteobacterium Yersinia enterocolitica are similar to Aliivibrio fischeri LuxR and LuxI.
Three-dimensional structures of proteins involved in quorum sensing were first published in 2001, when the crystal structures of three LuxS orthologs were determined by X-ray crystallography. A database of quorum-sensing peptides is available under the name Quorumpeps. Certain bacteria can produce enzymes called lactonases that can target and inactivate AHLs. Researchers have developed novel molecules which block the signalling receptors of bacteria. BTL is a compound that has been shown to inhibit quorum sensing and decrease the amount of cell death by a significant amount.
Vibrio fischeri system occur in the Gram-negative Proteobacteria. Although examples of horizontal gene transfer are apparent in LuxI, LuxR, and LuxS phylogenies, they are relatively rare. This result is in line with the observation that quorum sensing genes tend to control the expression of a wide array of genes scattered throughout the bacterial chromosome. A recent acquisition by horizontal gene transfer would be unlikely to have integrated itself to this degree.
As quorum sensing implies a cooperative behavior, this concept has been challenged by the evolutionary implication of cooperative cheaters. This is circumvented by the concept of diffusion sensing, which has been an alternative and complementary model to quorum sensing. Next to the potential antimicrobial functionality, quorum-sensing derived molecules, especially the peptides, are being investigated for their use in other therapeutic domains as well, including immunology, central nervous system disorders and oncology. Methanosaeta harundinacea 6Ac, a methanogenic archaeon, produces carboxylated acyl homoserine lactone compounds that facilitate the transition from growth as short cells to growth as filaments.
This article may require copy editing for use of English. You can assist by editing it. Quorum sensing was described when it was known that bacteria possess the ability to communicate. Hence, in the last few years, there are interactions shown between bacteria and eukaryotic hosts, like plants. These interactions are carried in presence of quorum sensing molecules which play a major role in maintaining the pathogenicity of bacteria towards other hosts like humans. A phenomenon called AHL Priming which is a dependent signalling pathway enhanced the knowledge for long chain AHLs. Looking towards developing new strategies based on plant-associated microbiomes it is aimed to improve the food supply and quality.