Quorum sensing
In a series of publications from 1998 to 2001, Bonnie Bassler showed that quorum sensing is not just an isolated mechanism in Aliivibrio fischeri, but is used ubiquitously across bacteria to communicate.
[7][13][8] In 1994, after study of the phenomenon had expanded into several additional bacteria, Stephen Winans did not believe the word autoinduction fully characterized the true process so, in a review article coauthored with W. Claiborne Fuqua and E. Peter Greenberg,[14] he introduced the term quorum sensing.
At high cell density, the local concentration of signaling molecules may exceed its threshold level, and trigger changes in gene expression.
is a gram-negative curved rod-formed bacterium which is the main colonizer of the epithelial cell surfaces of the early branching metazoan Hydra vulgaris.
[22] The ability of E. faecalis to form biofilms contributes to its capacity to survive in extreme environments, and facilitates its involvement in persistent bacterial infection, particularly in the case of multi-drug resistant strains.
[27] When AHL is detected, SdiA regulates the rck operon on the Salmonella virulence plasmid (pefI-srgD-srgA-srgB-rck-srgC) and a single gene horizontal acquisition in the chromosome srgE.
"[32] The pilus propelled microorganism moves with the use of both S- and A- (or gliding) motility, which provide transportation across a dynamic range of different surfaces.
[33] M. xanthus's A-motility is most effective in the presence of a single or low number of cells, allowing the bacteria to glide in high agar concentrations.
[34] Although the precise specifics of M. xanthus's communication methods for quorum sensing are not well understood, the bacteria mediate the process by using both C-signal and A-factor.
[32] Staphylococcus aureus is a type of pathogen that causes infection to the skin and soft tissue and can lead to a variety of more severe diseases such as osteomyelitis, pneumonia, and endocarditis.
[37] The environmental bacterium and opportunistic pathogen Pseudomonas aeruginosa uses quorum sensing to coordinate the formation of biofilm, swarming motility, exopolysaccharide production, virulence, and cell aggregation.
Quorum sensing in P. aeruginosa typically encompasses two complete AHL synthase-receptor circuits, LasI-LasR and RhlI-RhlR, as well as the orphan receptor-regulator QscR, which is also activated by the LasI-generated signal.
A comparative genomic and phylogenetic analysis of 138 genomes of bacteria, archaea, and eukaryotes found that "the LuxS enzyme required for AI-2 synthesis is widespread in bacteria, while the periplasmic binding protein LuxP is present only in Vibrio strains," leading to the conclusion that either "other organisms may use components different from the AI-2 signal transduction system of Vibrio strains to sense the signal of AI-2 or they do not have such a quorum sensing system at all.
[57] This family of quorum-sensing homologs may have arisen in the Gammaproteobacteria ancestor, although the cause of their extreme sequence divergence yet maintenance of functional similarity has yet to be explained.
[56][57] 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.
At this point, it is energetically unfavorable for intracellular autoinducers to leave the cell and they bind to receptors and trigger a signaling cascade to initiate gene expression and begin secreting an extracellular polysaccharide to encase themselves inside.
[64] One modern method of preventing biofilm development without the use of antibiotics is with anti-QS substances, such (naringenin, taxifolin, etc) that can be utilized as alternative form of therapy against bacterial virulence.
[69] This decision is crucial as it affects their replication strategy and potential to spread within the host population, optimizing their survival and proliferation under varying environmental conditions.
By synchronizing their life cycles, bacteriophages can maximize their impact on the host population, potentially leading to more effective control of bacterial densities.
This mechanism can be understood by looking at the effects of N-Acyl homoserine lactone (AHL), one of the quorum sensing-signaling molecules in gram-negative bacteria, on plants.
The latter disrupts the synthesis of a class of signalling molecules known as N-acyl homoserine lactones (AHLs) by blocking the enoyl-acyl carrier protein (ACP) reductase.
[82] Recently, a well-studied quorum quenching bacterial strain (KM1S) was isolated and its AHL degradation kinetics were studied using rapid resolution liquid chromatography (RRLC).
In this case, the outcomes differ from simple QS inactivation: the host modification results in a phenotypic switch of Curvibacter, which modifies its ability to colonize the epithelial cell surfaces of H.
[21] Applications of quorum quenching that have been exploited by humans include the use of AHL-degrading bacteria in aquacultures to limit the spread of diseases in aquatic populations of fish, mollusks and crustaceans.
[85][86] Anti-biofouling is another process that exploits quorum quenching bacteria to mediate the dissociation of unwanted biofilms aggregating on wet surfaces, such as medical devices, transportation infrastructure and water systems.
[85][87] Quorum quenching is recently studied for the control of fouling and emerging contaminants in electro membrane bioreactors (eMBRs) for the advanced treatment of wastewater.
Thus, although no single worker may have visited and compared all of the available options, quorum sensing enables the colony as a whole to quickly make good decisions about where to move.
Once the visitors to a new site sense that a quorum number (usually 10–20 bees) has been reached, they return to the swarm and begin using a new recruitment method called piping.
[101] Remarkable advancements have been and are continuing to be made in recent years in our understanding of synthetic biology in terms of endocrine and paracrine signaling mechanisms, and the myriad of modes by which bacteria record domestic and foreign cell numbers.
[102] The modulation of gene expression in response to oscillations in cell-population density is thanks to the QS techniques regulating bacterial communication natural and artificial cultures.
