View source for Quorum sensing

{{Short description|Biological ability to detect and respond to cell population density}}

{{More citations needed|date=April 2024}}
In [[biology]], '''quorum sensing''' or '''quorum signaling''' ('''QS''')<ref name="Lupp-et-al-2003" /> is the process of cell-to-cell communication<ref>{{cite journal | pmc=3543102 | date=2012 | last1=Rutherford | first1=S. T. | last2=Bassler | first2=B. L. | title=Bacterial Quorum Sensing: Its Role in Virulence and Possibilities for Its Control | journal=Cold Spring Harbor Perspectives in Medicine | volume=2 | issue=11 | pages=a012427 | doi=10.1101/cshperspect.a012427 | pmid=23125205 }}</ref> that allows bacteria to detect and respond to cell [[population density]] by [[gene regulation]], typically as a means of acclimating to environmental disadvantages.<ref name=":7" />

More specifically, quorum sensing is a type of cellular signaling, and more specifically can be considered a type of [[paracrine signaling]]. However, it also contains traits of [[autocrine signaling]]: a cell produces both an [[autoinducer]] molecule and the receptor for the autoinducer.<ref name=":7">{{Cite journal |last1=Postat |first1=J |last2=Bousso |first2=P |date=September 11, 2019 |title=Quorum Sensing by Monocyte-Derived Populations |journal=Frontiers in Immunology |volume=10 |issue=2140 |page=2140 |doi=10.3389/fimmu.2019.02140 |pmid=31572366 |pmc=6749007 |doi-access=free}}</ref> As one example, QS enables [[bacteria]] to restrict the expression of specific [[gene]]s to the high cell densities at which the resulting [[phenotype]]s will be most beneficial, especially for phenotypes that would be ineffective at low cell densities and therefore too energetically costly to express.<ref>{{Cite journal|last1=Papenfort |first1=K |last2=Bassler |first2=B |date=February 11, 2017 |title=Quorum-Sensing Signal-Response Systems in Gram-Negative Bacteria |journal=Nature Reviews Microbiology |volume=14 |issue=9 |pages=576–588 |doi=10.1038/nrmicro.2016.89 |pmid=27510864 |pmc=5056591 }}</ref> Many species of bacteria use quorum sensing to coordinate [[gene expression]] according to the density of their local population. In a similar fashion, some [[social insects]] use quorum sensing to determine where to nest. Quorum sensing in pathogenic bacteria activates host immune signaling and prolongs host survival, by limiting the bacterial intake of nutrients, such as [[tryptophan]], which further is converted to [[serotonin]].<ref name=":4">{{cite journal|vauthors=Jugder BE, Batista JH, Gibson JA, Cunningham PM, Asara JM, Watnick PI |title=Vibrio cholerae high cell density quorum sensing activates the host intestinal innate immune response |journal=Cell Reports |volume=40 |issue=12 |pages=111368 |date=September 2022 |pmid=36130487 |doi=10.1016/j.celrep.2022.111368 |pmc=9534793}}</ref> As such, quorum sensing allows a [[Commensalism|commensal]] interaction between host and pathogenic bacteria.<ref name=":4" /> Quorum sensing may also be useful for cancer cell communications.<ref>{{cite journal |vauthors=Ali I, Alfarouk KO, Reshkin SJ, Ibrahim ME |title=Doxycycline as Potential Anti-cancer Agent |journal=Anti-Cancer Agents in Medicinal Chemistry |volume=17 |issue=12 |pages=1617–1623 |date=16 January 2018 |pmid=28270076 |doi=10.2174/1871520617666170213111951}}</ref>

In addition to its function in biological systems, quorum sensing has several useful applications for computing and robotics. In general, quorum sensing can function as a decision-making process in any [[decentralized system]] in which the components have: (a) a means of assessing the number of other components they interact with and (b) a standard response once a threshold to achieve number of components is useful for amino acid regulation 
is detected.
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==Discovery==
The first observations of an autoinducer-controlled phenotype in bacteria were reported in 1970, by Kenneth Nealson, Terry Platt, and [[J. Woodland Hastings]],<ref name="Nealson-et-al-1970">{{cite journal | vauthors = Nealson KH, Platt T, Hastings JW | title = Cellular control of the synthesis and activity of the bacterial luminescent system | journal = Journal of Bacteriology | volume = 104 | issue = 1 | pages = 313–322 | date = October 1970 | pmid = 5473898 | pmc = 248216 | doi = 10.1128/jb.104.1.313-322.1970 }}</ref> who observed what they described as a conditioning of the medium in which they had grown the [[bioluminescent]] marine bacterium ''[[Aliivibrio fischeri]]''.<ref name="Bodman-et-al-2003" /> These bacteria did not synthesize [[luciferase]]—and therefore did not luminesce—in freshly inoculated culture but only after the bacterial population had increased significantly.

==Etymology==
Because Nealson, Platt, and Hastings attributed the conditioning of the growth medium to the growing population of cells itself, they referred to the phenomenon as autoinduction.<ref name="Nealson-et-al-1970" /><ref name="Nealson-1977" /><ref name="Bodman-et-al-2003" /> 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,<ref>{{Cite journal |last1=Fuqua |first1=W C |last2=Winans |first2=S C |last3=Greenberg |first3=E P |date=January 1994 |title=Quorum sensing in bacteria: the LuxR-LuxI family of cell density-responsive transcriptional regulators |journal=Journal of Bacteriology |volume=176 |issue=2 |pages=269–275 |doi=10.1128/jb.176.2.269-275.1994 |pmc=205046 |pmid=8288518}}</ref> he introduced the term ''quorum sensing''. Its use also avoided confusion between the terms ''autoinduction'' and ''[[autoregulation]]''.

The new term was not stumbled onto, but rather created through trial and error. Among the alternatives that Winans had created and considered were ''gridlockins'', ''communiolins'', and ''quoromones''.<ref name="Turovskiy Kashtanov Paskhover Chikindas 2007">{{cite book |doi=10.1016/S0065-2164(07)62007-3 |chapter=Quorum Sensing: Fact, Fiction, and Everything in Between |title=Advances in Applied Microbiology Volume 62 |date=2007 |last1=Turovskiy |first1=Yevgeniy |last2=Kashtanov |first2=Dimitri |last3=Paskhover |first3=Boris |last4=Chikindas |first4=Michael L. |journal=Advances in Applied Microbiology |volume=62 |pages=191–234 |pmid=17869606 |pmc=2391307 |isbn=978-0-12-373669-7 }}</ref>

==Bacteria==
{{microbial and microbot movement|collective}}
[[File:Quorum sensing of Gram Negative cell.pdf|thumb|upright=1.2|Quorum sensing of gram-negative cell]]
[[File:Gram Positive Bacteria Quorum Sensing.pdf|thumb|upright=1.2|Gram-positive bacteria quorum sensing]]

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 behaviors. Some common phenotypes include [[biofilm]] formation, [[virulence]] factor expression, and [[motility]]. Certain bacteria are able to use quorum sensing to regulate [[bioluminescence]], [[nitrogen fixation]] and [[Spore|sporulation]].<ref name=":0">{{cite journal | vauthors = Pan J, Ren D | title = Quorum sensing inhibitors: a patent overview | journal = Expert Opinion on Therapeutic Patents | volume = 19 | issue = 11 | pages = 1581–1601 | date = November 2009 | pmid = 19732032 | doi = 10.1517/13543770903222293 | s2cid = 30007165 }}</ref>

The quorum-sensing function is based on the local density of the bacterial population in the immediate environment.<ref name="Miller Bassler 2001"/> It can occur within a single bacterial species, as well as between diverse species. Both [[gram-positive bacteria|gram-positive]] and [[gram-negative bacteria|gram-negative]] bacteria use quorum sensing, but there are some major differences in their mechanisms.<ref name=":1">{{cite journal | vauthors = Bassler BL | title = How bacteria talk to each other: regulation of gene expression by quorum sensing | journal = Current Opinion in Microbiology | volume = 2 | issue = 6 | pages = 582–587 | date = December 1999 | pmid = 10607620 | doi = 10.1016/s1369-5274(99)00025-9 }}</ref>

===Mechanism===
For the bacteria to use quorum sensing constitutively, they must possess three abilities: secretion of a signaling molecule, secretion of an [[autoinducer]] (to detect the change in concentration of signaling molecules), and regulation of gene [[Transcription (biology)|transcription]] as a response.<ref name=":0" /> This process is highly dependent on the [[diffusion]] mechanism of the signaling molecules. QS signaling molecules are usually secreted at a low level by individual bacteria. At low cell density, the molecules may just diffuse away. At high cell density, the local concentration of signaling molecules may exceed its threshold level, and trigger changes in gene expression.<ref name=":1" />

====Gram-positive bacteria====
Gram-positive bacteria use [[Autoinducer#Peptides|autoinducing peptide]]s (AIP) as their autoinducers.<ref name=":2">{{cite journal | vauthors = Rutherford ST, Bassler BL | title = Bacterial quorum sensing: its role in virulence and possibilities for its control | journal = Cold Spring Harbor Perspectives in Medicine | volume = 2 | issue = 11 | pages = a012427 | date = November 2012 | pmid = 23125205 | pmc = 3543102 | doi = 10.1101/cshperspect.a012427 }}</ref>

When gram-positive bacteria detect high concentration of AIPs in their environment, that happens by way of AIPs binding to a receptor to activate a [[kinase]]. The kinase [[phosphorylation|phosphorylates]] a [[transcription factor]], which regulates gene transcription. This is called a [[two-component regulatory system|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.<ref name=":2" />

====Gram-negative bacteria====
Gram-negative bacteria produce [[N-Acyl homoserine lactone|N-acyl homoserine lactones]] (AHL) as their signaling molecule.<ref name=":2" /> Usually AHLs do not need additional processing, and bind directly to transcription factors to regulate gene expression.<ref name=":1" />

Some gram-negative bacteria may use the two-component system as well.<ref name=":2" />

===Examples===

====''Aliivibrio fischeri''====
The bioluminescent bacterium ''[[Aliivibrio fischeri]]'' is the first organism in which QS was observed. It lives as a [[mutualism (biology)|mutualistic]] [[symbiont]] in the [[photophore]] (or light-producing organ) of the [[Hawaiian bobtail squid]]. When ''A. fischeri'' cells are free-living (or [[plankton]]ic), the autoinducer is at low concentration, and, thus, cells do not show luminescence. However, when the population reaches the threshold in the photophore (about {{10^|11}} cells/ml), transcription of [[luciferase]] is induced, leading to [[bioluminescence]].
In ''A. fischeri'', bioluminescence is regulated by AHLs (N-acyl-homoserine lactones) which is a product of the LuxI gene whose transcription is regulated by the LuxR activator. LuxR works only when AHLs binds to the LuxR.

====''Curvibacter'' sp.====
[[Curvibacter|''Curvibacter'' sp.]] 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]]''.<ref>{{Cite web|url=https://www.researchgate.net/publication/45278794|title=Curvibacter fontana sp. nov., a microaerobic bacteria isolated from well water|website=ResearchGate|language=en|access-date=2019-03-13}}</ref><ref name=":3">{{cite journal | vauthors = Pietschke C, Treitz C, Forêt S, Schultze A, Künzel S, Tholey A, Bosch TC, Fraune S | display-authors = 6 | title = Host modification of a bacterial quorum-sensing signal induces a phenotypic switch in bacterial symbionts | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 114 | issue = 40 | pages = E8488–E8497 | date = October 2017 | pmid = 28923926 | pmc = 5635886 | doi = 10.1073/pnas.1706879114 | bibcode = 2017PNAS..114E8488P | doi-access = free }}</ref> Sequencing the complete [[Genome#Prokaryotic genomes|genome]] uncovered a circular chromosome (4.37 Mb), a plasmid (16.5 kb), and two [[operon]]s coding each for an AHL (N-acyl-homoserine lactone) synthase (''curI1'' and ''curI2'') and an AHL receptor (''curR1'' and ''curR2'').<ref name=":3" /> Moreover, a study showed that these host associated ''Curvibacter'' bacteria produce a broad spectrum of AHL, explaining the presence of those operons.<ref name=":3" /> As mentioned before, AHL are the quorum sensing molecules of gram-negative bacteria, which means ''Curvibacter'' has a quorum sensing activity.

Even though their function in host-microbe interaction is largely unknown, ''Curvibacter'' quorum-sensing signals are relevant for host-microbe interactions.<ref name=":3" /> Indeed, due to the [[oxidoreductase]] activity of ''Hydra'', there is a modification of AHL signalling molecules (3-oxo-homoserine lactone into 3-hydroxy-homoserine lactone) which leads to a different host-microbe interaction. On one hand, a phenotypic switch of the colonizer ''Curvibacter'' takes place. The most likely explanation is that the binding of 3-oxo-HSL and 3-hydroxy-HSL causes different conformational changes in the AHL receptors ''curR1'' and ''curR2''. As a result, there is a different DNA-binding motif affinity and thereby different target genes are activated.<ref name=":3" /> On the other hand, this switch modifies its ability to colonize the epithelial cell surfaces of ''Hydra vulgaris''.<ref name=":3" /> Indeed, one explanation is that with a 3-oxo-HSL quorum-sensing signal, there is an up-regulation of flagellar assembly. Yet, [[flagellin]], the main protein component of flagella, can act as an immunomodulator and activate the innate immune response in ''Hydra''. Therefore, bacteria have less chance to evade the immune system and to colonize host tissues.<ref name=":3" /> Another explanation is that 3-hydroxy-HSL induces carbon metabolism and fatty acid degradation genes in ''Hydra''. This allows the bacterial metabolism to adjust itself to the host growth conditions, which is essential for the colonization of the ectodermal mucus layer of ''Hydrae''.<ref name=":3" />

==== ''Enterococcus faecalis'' ====
''[[Enterococcus faecalis]]'' is an opportunistic, gram-positive bacteria that forms biofilm in glass. This process is also known as forming a biofilm in vitro. The presence of (Esp), a certain cell surface protein, aids the formation of a biofilm by ''E. faecalis''.<ref>{{cite journal | pmc=365672 | date=2004 | last1=Kristich | first1=C. J. | last2=Li | first2=Y. H. | last3=Cvitkovitch | first3=D. G. | last4=Dunny | first4=G. M. | title=Esp-Independent Biofilm Formation by Enterococcus faecalis | journal=Journal of Bacteriology | volume=186 | issue=1 | pages=154–163 | doi=10.1128/JB.186.1.154-163.2004 | pmid=14679235 }}</ref>

The ability of ''E. faecalis'' to form [[biofilm]]s 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.<ref name = Schiopu2023>{{cite journal |vauthors=Șchiopu P, Toc DA, Colosi IA, Costache C, Ruospo G, Berar G, Gălbău ȘG, Ghilea AC, Botan A, Pană AG, Neculicioiu VS, Todea DA |title=An Overview of the Factors Involved in Biofilm Production by the Enterococcus Genus |journal=Int J Mol Sci |volume=24 |issue=14 |date=July 2023 |page=11577 |pmid=37511337 |pmc=10380289 |doi=10.3390/ijms241411577 |doi-access=free |url=}}</ref>  Biofilm formation in ''E. faecalis'' is associated with [[DNA]] release, and such release has emerged as a fundamental aspect of biofilm formation.<ref name = Schiopu2023/>  Conjugative [[plasmid]] DNA transfer in ''E. faecalis'' is enhanced by the release of peptide [[sex pheromone]]s.<ref>{{cite journal |vauthors=Hirt H, Greenwood-Quaintance KE, Karau MJ, Till LM, Kashyap PC, Patel R, Dunny GM |title=Enterococcus faecalis Sex Pheromone cCF10 Enhances Conjugative Plasmid Transfer In Vivo |journal=mBio |volume=9 |issue=1 |pages= |date=February 2018 |pmid=29440568 |pmc=5821081 |doi=10.1128/mBio.00037-18 |url=}}</ref>

==== ''Escherichia coli'' ====
In the gram-negative bacterium ''[[Escherichia coli]]'', cell division may be partially regulated by [[AI-2]]-mediated quorum sensing. This species uses AI-2, which is produced and processed by the ''[[Lipolysis-stimulated lipoprotein receptor|lsr]]'' [[operon]]. Part of it encodes an [[ABC transporter]], which imports AI-2 into the cells during the early stationary (latent) phase of growth. AI-2 is then phosphorylated by the LsrK [[kinase]], and the newly produced phospho-AI-2 can be either internalized or used to suppress LsrR, a repressor of the ''lsr'' operon (thereby activating the operon). Transcription of the ''lsr'' operon is also thought to be inhibited by [[dihydroxyacetone phosphate]] (DHAP) through its competitive binding to LsrR. [[Glyceraldehyde 3-phosphate]] has also been shown to inhibit the ''lsr'' operon through [[Cyclic adenosine monophosphate|cAMP]]-CAPK-mediated inhibition. This explains why, when grown with [[glucose]], ''E. coli'' will lose the ability to internalize AI-2 (because of [[catabolite repression]]). When grown normally, [[AI-2]] presence is transient.

''E. coli'' and ''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.<ref>{{cite journal | vauthors = Ahmer BM | title = Cell-to-cell signalling in Escherichia coli and Salmonella enterica | journal = Molecular Microbiology | volume = 52 | issue = 4 | pages = 933–945 | date = May 2004 | pmid = 15130116 | doi = 10.1111/j.1365-2958.2004.04054.x | doi-access = free }}</ref> AHL quorum sensing regulates a wide range of genes through cell density. Other species of bacteria produce AHLs that ''Escherichia'' and ''Salmonella'' can detect. ''E. coli'' and ''Salmonella'' produce a receptor like protein (SdiA) allowing the amino acid sequence that is similar to AHL show AHLs can be found in the bovine rumen and ''E. coli'' responds to AHLs taken out of the bovine rumen. Most animals do not have AHL in their gastrointestinal tracts.<ref>{{cite journal | pmc=3078957 | date=2011 | last1=Soares | first1=J. A. | last2=Ahmer | first2=B. M. | title=Detection of acyl-homoserine lactones by Escherichia and Salmonella | journal=Current Opinion in Microbiology | volume=14 | issue=2 | pages=188–193 | doi=10.1016/j.mib.2011.01.006 | pmid=21353625 }}</ref>

====''Salmonella enterica''====
''[[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]]''.<ref>{{cite journal | vauthors = Michael B, Smith JN, Swift S, Heffron F, Ahmer BM | title = SdiA of Salmonella enterica is a LuxR homolog that detects mixed microbial communities | journal = Journal of Bacteriology | volume = 183 | issue = 19 | pages = 5733–5742 | date = October 2001 | pmid = 11544237 | pmc = 95466 | doi = 10.1128/JB.183.19.5733-5742.2001 }}</ref> 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''.<ref>{{cite journal | vauthors = Ahmer BM, van Reeuwijk J, Timmers CD, Valentine PJ, Heffron F | title = Salmonella typhimurium encodes an SdiA homolog, a putative quorum sensor of the LuxR family, that regulates genes on the virulence plasmid | journal = Journal of Bacteriology | volume = 180 | issue = 5 | pages = 1185–1193 | date = March 1998 | pmid = 9495757 | pmc = 107006 | doi = 10.1128/JB.180.5.1185-1193.1998 }}</ref><ref>{{cite journal | vauthors = Smith JN, Ahmer BM | title = Detection of other microbial species by Salmonella: expression of the SdiA regulon | journal = Journal of Bacteriology | volume = 185 | issue = 4 | pages = 1357–1366 | date = February 2003 | pmid = 12562806 | pmc = 142872 | doi = 10.1128/JB.185.4.1357-1366.2003 }}</ref> ''Salmonella'' does not detect AHL when passing through the gastrointestinal tracts of several animal species, suggesting that the normal microbiota does not produce AHLs. However, SdiA does become activated when ''Salmonella'' transits through turtles colonized with ''Aeromonas hydrophila'' or mice infected with ''Yersinia enterocolitica''.<ref>{{cite journal | vauthors = Smith JN, Dyszel JL, Soares JA, Ellermeier CD, Altier C, Lawhon SD, Adams LG, Konjufca V, Curtiss R, Slauch JM, Ahmer BM | display-authors = 6 | title = SdiA, an N-acylhomoserine lactone receptor, becomes active during the transit of Salmonella enterica through the gastrointestinal tract of turtles | journal = PLOS ONE | volume = 3 | issue = 7 | pages = e2826 | date = July 2008 | pmid = 18665275 | pmc = 2475663 | doi = 10.1371/journal.pone.0002826 | bibcode = 2008PLoSO...3.2826S | doi-access = free | editor = Ausubel, Frederick M. }}</ref><ref>{{cite journal | vauthors = Dyszel JL, Smith JN, Lucas DE, Soares JA, Swearingen MC, Vross MA, Young GM, Ahmer BM | display-authors = 6 | title = Salmonella enterica serovar Typhimurium can detect acyl homoserine lactone production by Yersinia enterocolitica in mice | journal = Journal of Bacteriology | volume = 192 | issue = 1 | pages = 29–37 | date = January 2010 | pmid = 19820103 | pmc = 2798265 | doi = 10.1128/JB.01139-09 }}</ref> Therefore, ''Salmonella'' appears to use SdiA to detect the AHL production of other pathogens rather than the normal gut flora.

====''Myxococcus xanthus''====
''[[Myxococcus]]'' is a genus of gram-negative bacterium in the Myxococcacae family. ''[[Myxococcus xanthus]]'' specifically, a bacillus myxobacteria species within [[Myxococcaceae|Myxococcae]], grows in the upper layers of soil. This bacterium is known for its unique utilization of quorum sensing practices to hunt.

The bacterium uniquely survives not on sugars, but [[lipid]]s created by the degradation of macromolecules lysed by the species. It hunts and feeds through a density-regulated method of predation that is "the regulation of gene expression in response to cell density."<ref name=":8">{{Cite journal| doi = 10.1111/j.1574-6976.2009.00185.x| issn = 0168-6445| volume = 33| issue = 5| pages = 942–957| last1 = Berleman| first1 = James E.| last2 = Kirby| first2 = John R.| title = Deciphering the hunting strategy of a bacterial wolfpack| journal = FEMS Microbiology Reviews| access-date = 2024-04-16| date = 2009-09-01| pmid = 19519767| pmc = 2774760| url = https://doi.org/10.1111/j.1574-6976.2009.00185.x}}</ref> 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.<ref>{{Cite journal| issn = 0027-8424| volume = 90| issue = 8| pages = 3378–3382| last1 = Shi| first1 = W| last2 = Zusman| first2 = D R| title = The two motility systems of Myxococcus xanthus show different selective advantages on various surfaces.| journal = Proceedings of the National Academy of Sciences of the United States of America| date = 1993-04-15| doi = 10.1073/pnas.90.8.3378| doi-access = free| pmid = 8475084| pmc = 46303| bibcode = 1993PNAS...90.3378S}}</ref>  ''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. The S-motility, or social motility, is controlled by the process of quorum sensing and is only effective when cells are within one cell length of a neighbor.<ref>{{Cite journal| doi = 10.1371/journal.pcbi.1005010| issn = 1553-7358| volume = 12| issue = 6| pages = –1005010| last1 = Patra| first1 = Pintu| last2 = Kissoon| first2 = Kimberley| last3 = Cornejo| first3 = Isabel| last4 = Kaplan| first4 = Heidi B.| last5 = Igoshin| first5 = Oleg A.| title = Colony Expansion of Socially Motile Myxococcus xanthus Cells Is Driven by Growth, Motility, and Exopolysaccharide Production| journal = PLOS Computational Biology| date = 2016-06-30| doi-access = free| pmid = 27362260| pmc = 4928896| bibcode = 2016PLSCB..12E5010P}}</ref>  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. The A-factor molecule, produced by ''M. xanthus'', must reach a set concentration to initiate aggregation for hunting.<ref>{{Cite journal| doi = 10.3389/fmicb.2017.00439| issn = 1664-302X| volume = 8| pages = 439| last1 = Lloyd| first1 = Daniel G.| last2 = Whitworth| first2 = David E.| title = The Myxobacterium Myxococcus xanthus Can Sense and Respond to the Quorum Signals Secreted by Potential Prey Organisms| journal = Frontiers in Microbiology| date = 2017-03-14| doi-access = free| pmid = 28352265| pmc = 5348527}}</ref>  The C-signal concentration, on the other hand, plays a role in [[Fruiting body (bacteria)|fruiting body]] production.

The species is known for its ability to use quorum sensing to hunt in special packs with thousands of individual cells, lending to ''M. xanthus''{{'s}} name "the wolf packs." ''M. xanthus'' is inclined to behave in a [[Multicellular organism|multicellular]] fashion. In the presence of many cells, it uses these "wolf packs" to form "highly structured [[biofilm]]s that include tentacle-like packs of surface-gliding cell groups, synchronized rippling waves of oscillating cells and massive spore-filled aggregates that protrude upwards from the substratum to form fruiting bodies."<ref>{{Cite journal| doi = 10.3389/fmicb.2022.894562| issn = 1664-302X| volume = 13| pages = 894562| last1 = Dye| first1 = Keane J.| last2 = Yang| first2 = Zhaomin| title = Analysis of Myxococcus xanthus Vegetative Biofilms With Microtiter Plates| journal = Frontiers in Microbiology| date = 2022-04-29| doi-access = free| pmid = 35572678| pmc = 9100584}}</ref><ref name=":8" /> On the fringes of this film, individual cells can be observed "gliding across the surface, but the majority of cells are observed in large tendril-shaped groups" using S-motility.<ref name=":8" />

==== ''Staphylococcus aureus'' ====
''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. ''S. aureus'' uses biofilms in order to increase its chances of survival by becoming resistant to antibiotics. Biofilms help ''S. aureus'' become up to 1500 times more resistant to antibiofilm agents, which try to break down biofilms formed by ''S. aureus''.<ref>{{cite journal |last1=Wu |first1=Xiying |last2=Wang |first2=Huan |last3=Xiong |first3=Juan |last4=Yang |first4=Guo-Xun |last5=Hu |first5=Jin-Feng |last6=Zhu |first6=Quangang |last7=Chen |first7=Zhongjian |title=Staphylococcus aureus biofilm: Formulation, regulatory, and emerging natural products-derived therapeutics |journal=Biofilm |date=June 2024 |volume=7 |pages=100175 |doi=10.1016/j.bioflm.2023.100175 |pmid=38298832 |pmc=10827693 }}</ref>

====''Pseudomonas aeruginosa''====
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.<ref>{{cite journal | vauthors = Sauer K, Camper AK, Ehrlich GD, Costerton JW, Davies DG | title = Pseudomonas aeruginosa displays multiple phenotypes during development as a biofilm | journal = Journal of Bacteriology | volume = 184 | issue = 4 | pages = 1140–1154 | date = February 2002 | pmid = 11807075 | pmc = 134825 | doi = 10.1128/jb.184.4.1140-1154.2002 }}</ref> These bacteria can grow within a host without harming it until they reach a threshold concentration. Then they become aggressive, developing to the point at which their numbers are sufficient to overcome the host's [[immune system]], and form a [[biofilm]], leading to [[disease]] within the host as the biofilm is a protective layer encasing the bacterial population.{{citation needed|date=July 2022}} The relative ease of growth, handling, and genetic manipulation of ''P. aeruginosa'' has lent much research effort to the quorum sensing circuits of this relatively common bacterium. 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.<ref>{{cite journal |last1=Schuster |first1=Martin |last2=Peter Greenberg |first2=E. |title=A network of networks: Quorum-sensing gene regulation in Pseudomonas aeruginosa |journal=International Journal of Medical Microbiology |date=April 2006 |volume=296 |issue=2–3 |pages=73–81 |doi=10.1016/j.ijmm.2006.01.036 |pmid=16476569 }}</ref> Together, the multiple AHL quorum sensing circuits of ''P. aeruginosa'' influence regulation of hundreds of genes.

Another form of [[gene regulation]] that allows the [[bacteria]] to rapidly adapt to surrounding changes is through environmental signaling. Recent studies have discovered that [[anaerobiosis]] can significantly impact the major regulatory circuit of quorum sensing. This important link between quorum sensing and anaerobiosis has a significant impact on the production of virulence factors of this [[organism]].<ref name="Cornelis">{{cite book |editor=Cornelis, P. |title=Pseudomonas: Genomics and Molecular Biology |url= http://www.horizonpress.com/pseudo |edition=1st |year=2008 |publisher=Caister Academic Press |isbn=978-1-904455-19-6 |access-date=1 May 2022}}</ref> There is hope among some humans that the therapeutic enzymatic degradation of the signaling molecules will be possible when treating illness caused by biofilms, and prevent the formation of such biofilms and possibly weaken established biofilms. Disrupting the signaling process in this way is called ''quorum sensing inhibition''.<ref>{{cite journal |last1=Ma |first1=Yeping |last2=Tang |first2=Wing Suet |last3=Liu |first3=Sylvia Yang |last4=Khoo |first4=Bee Luan |last5=Chua |first5=Song Lin |title=Juglone as a Natural Quorum Sensing Inhibitor against Pseudomonas aeruginosa pqs-Mediated Virulence and Biofilms |journal=ACS Pharmacology & Translational Science |date=9 February 2024 |volume=7 |issue=2 |pages=533–543 |doi=10.1021/acsptsci.3c00354 |pmid=38357290 |pmc=10863437 |pmc-embargo-date=January 25, 2025 }}</ref>

====''Acinetobacter'' sp.====
It has recently been found that ''[[Acinetobacter]]'' sp. also show quorum sensing activity. This bacterium, an emerging pathogen, produces AHLs.<ref name="biomedcentral">{{cite journal | vauthors = Chan KG, Atkinson S, Mathee K, Sam CK, Chhabra SR, Cámara M, Koh CL, Williams P | display-authors = 6 | title = Characterization of N-acylhomoserine lactone-degrading bacteria associated with the Zingiber officinale (ginger) rhizosphere: co-existence of quorum quenching and quorum sensing in Acinetobacter and Burkholderia | journal = BMC Microbiology | volume = 11 | issue = 1 <!-- |access-date=1 May 2022 --> | pages = 51 | date = March 2011 | pmid = 21385437 | pmc = 3062576 | doi = 10.1186/1471-2180-11-51 | doi-access = free }}</ref> ''Acinetobacter'' sp. shows both quorum sensing and quorum quenching activity. It produces AHLs and can also degrade the AHL molecules.<ref name="biomedcentral"/>

====''Aeromonas'' sp.====
This bacterium was previously considered a fish pathogen, but it has recently emerged as a human pathogen.<ref>{{cite journal | vauthors = Igbinosa IH, Igumbor EU, Aghdasi F, Tom M, Okoh AI | title = Emerging Aeromonas species infections and their significance in public health | journal = TheScientificWorldJournal | volume = 2012 | pages = 625023 | year = 2012 | pmid = 22701365 | pmc = 3373137 | doi = 10.1100/2012/625023 | doi-access = free }}</ref> ''[[Aeromonas]]'' sp. have been isolated from various infected sites from patients (bile, blood, peritoneal fluid, pus, stool and urine). All isolates produced the two principal AHLs, N-butanoylhomoserine lactone (C4-HSL) and N-hexanoyl homoserine lactone (C6-HSL). It has been documented that ''Aeromonas sobria'' has produced C6-HSL and two additional AHLs with N-acyl side chain longer than C6.<ref name="Current Microbiology">{{cite journal | vauthors = Chan KG, Puthucheary SD, Chan XY, Yin WF, Wong CS, Too WS, Chua KH | title = Quorum sensing in Aeromonas species isolated from patients in Malaysia | journal = Current Microbiology | volume = 62 | issue = 1 | pages = 167–172 | date = January 2011 | pmid = 20544198 | doi = 10.1007/s00284-010-9689-z | s2cid = 6761810 <!-- |access-date=1 May 2022 --> }}</ref>

====''Yersinia ''====
The YenR and YenI proteins produced by the [[gammaproteobacterium]] ''[[Yersinia enterocolitica]]'' are similar to ''Aliivibrio fischeri'' LuxR and LuxI.<ref>{{cite journal | vauthors = Throup JP, Camara M, Briggs GS, Winson MK, Chhabra SR, Bycroft BW, Williams P, Stewart GS | display-authors = 6 | title = Characterisation of the yenI/yenR locus from Yersinia enterocolitica mediating the synthesis of two N-acylhomoserine lactone signal molecules | journal = Molecular Microbiology | volume = 17 | issue = 2 | pages = 345–356 | date = July 1995 | pmid = 7494483 | doi = 10.1111/j.1365-2958.1995.mmi_17020345.x | s2cid = 3100775 }}</ref><ref name="Atkinson 1451–61">{{cite journal | vauthors = Atkinson S, Chang CY, Sockett RE, Cámara M, Williams P | title = Quorum sensing in Yersinia enterocolitica controls swimming and swarming motility | journal = Journal of Bacteriology | volume = 188 | issue = 4 | pages = 1451–1461 | date = February 2006 | pmid = 16452428 | pmc = 1367215 | doi = 10.1128/JB.188.4.1451-1461.2006 }}</ref> YenR activates the expression of a [[Bacterial small RNA|small non-coding RNA]], YenS. YenS inhibits YenI expression and acylhomoserine lactone production.<ref name="Tsai 556–71">{{cite journal | vauthors = Tsai CS, Winans SC | title = The quorum-hindered transcription factor YenR of Yersinia enterocolitica inhibits pheromone production and promotes motility via a small non-coding RNA | journal = Molecular Microbiology | volume = 80 | issue = 2 | pages = 556–571 | date = April 2011 | pmid = 21362062 | doi = 10.1111/j.1365-2958.2011.07595.x | doi-access = free }}</ref> YenR/YenI/YenS are involved in the control of swimming and swarming motility.<ref name="Atkinson 1451–61"/><ref name="Tsai 556–71"/>

===Molecules involved===
Three-dimensional structures of proteins involved in quorum sensing were first published in 2001, when the [[crystal structure]]s of three [[LuxS]] [[Homology (biology)#Orthology|orthologs]] were determined by [[X-ray crystallography]].<ref>{{cite journal | vauthors = Lewis HA, Furlong EB, Laubert B, Eroshkina GA, Batiyenko Y, Adams JM, Bergseid MG, Marsh CD, Peat TS, Sanderson WE, Sauder JM, Buchanan SG | display-authors = 6 | title = A structural genomics approach to the study of quorum sensing: crystal structures of three LuxS orthologs | journal = Structure | volume = 9 | issue = 6 | pages = 527–537 | date = June 2001 | pmid = 11435117 | doi = 10.1016/S0969-2126(01)00613-X | doi-access = free }}</ref> In 2002, the crystal structure of the receptor LuxP of ''[[Vibrio harveyi]]'' with its inducer [[AI-2]] (which is one of the few [[biomolecules]] containing [[boron]]) bound to it was also determined.<ref>{{cite journal | vauthors = Chen X, Schauder S, Potier N, Van Dorsselaer A, Pelczer I, Bassler BL, Hughson FM | title = Structural identification of a bacterial quorum-sensing signal containing boron | journal = Nature | volume = 415 | issue = 6871 | pages = 545–549 | date = January 2002 | pmid = 11823863 | doi = 10.1038/415545a }}</ref> Many bacterial species, including ''[[E. coli]]'', an enteric bacterium and model organism for gram-negative bacteria, produce AI-2. 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 space|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."<ref name="pmid15456522">{{cite journal | vauthors = Sun J, Daniel R, Wagner-Döbler I, Zeng AP | title = Is autoinducer-2 a universal signal for interspecies communication: a comparative genomic and phylogenetic analysis of the synthesis and signal transduction pathways | journal = BMC Evolutionary Biology | volume = 4 | issue = 1 | pages = 36 | date = September 2004 | pmid = 15456522 | pmc = 524169 | doi = 10.1186/1471-2148-4-36 | doi-access = free }}</ref> ''Vibrio'' species utilize [[Qrr RNA]]s, small non-coding RNAs, that are activated by these autoinducers to target cell density master regulators. [[Farnesol]] is used by the fungus ''[[Candida albicans]]'' as a quorum sensing molecule that inhibits [[filamentation]].<ref>{{cite journal | vauthors = Hornby JM, Jensen EC, Lisec AD, Tasto JJ, Jahnke B, Shoemaker R, Dussault P, Nickerson KW | display-authors = 6 | title = Quorum sensing in the dimorphic fungus Candida albicans is mediated by farnesol | journal = Applied and Environmental Microbiology | volume = 67 | issue = 7 | pages = 2982–2992 | date = July 2001 | pmid = 11425711 | pmc = 92970 | doi = 10.1128/AEM.67.7.2982-2992.2001 | bibcode = 2001ApEnM..67.2982H }}</ref>

A database of quorum-sensing peptides is available under the name Quorumpeps.<ref>{{cite journal | vauthors = Wynendaele E, Bronselaer A, Nielandt J, D'Hondt M, Stalmans S, Bracke N, Verbeke F, Van De Wiele C, De Tré G, De Spiegeleer B | display-authors = 6 | title = Quorumpeps database: chemical space, microbial origin and functionality of quorum sensing peptides | journal = Nucleic Acids Research | volume = 41 | issue = Database issue | pages = D655–D659 | date = January 2013 | pmid = 23180797 | pmc = 3531179 | doi = 10.1093/nar/gks1137 }}</ref><ref>{{cite journal | vauthors = Wynendaele E, Gevaert B, Stalmans S, Verbeke F, De Spiegeleer B | title = Exploring the chemical space of quorum sensing peptides | journal = Biopolymers | volume = 104 | issue = 5 | pages = 544–551 | date = September 2015 | pmid = 25846138 | doi = 10.1002/bip.22649 | s2cid = 21031922 }}</ref>

Certain bacteria can produce enzymes called [[lactonase]]s that can target and inactivate AHLs.
Researchers have developed novel molecules which block the signalling receptors of bacteria ("Quorum quenching"). mBTL is a compound that has been shown to inhibit quorum sensing and decrease the amount of cell death by a significant amount.<ref>{{cite journal | vauthors = O'Loughlin CT, Miller LC, Siryaporn A, Drescher K, Semmelhack MF, Bassler BL | title = A quorum-sensing inhibitor blocks Pseudomonas aeruginosa virulence and biofilm formation | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 110 | issue = 44 | pages = 17981–17986 | date = October 2013 | pmid = 24143808 | pmc = 3816427 | doi = 10.1073/pnas.1316981110 | bibcode = 2013PNAS..11017981O | doi-access = free }}</ref> 
Additionally, researchers are also examining the role of natural compounds (such as [[caffeine]]) as potential quorum sensing inhibitors.<ref>{{cite journal | vauthors = Norizan SN, Yin WF, Chan KG | title = Caffeine as a potential quorum sensing inhibitor | journal = Sensors | volume = 13 | issue = 4 | pages = 5117–5129 | date = April 2013 | pmid = 23598500 | pmc = 3673129 | doi = 10.3390/s130405117 | bibcode = 2013Senso..13.5117N | doi-access = free }}</ref> Research in this area has been promising and could lead to the development of natural compounds as effective therapeutics.

===Evolution===

====Sequence analysis====
The majority of quorum sensing systems that fall under the "two-gene" (an autoinducer synthase coupled with a receptor molecule) paradigm as defined by the ''[[Vibrio fischeri]]'' system occur in the [[gram-negative]] [[Pseudomonadota]]. A comparison between the Pseudomonadota [[phylogeny]] as generated by [[16S ribosomal RNA]] sequences and phylogenies of LuxI-, LuxR-, or LuxS-homologs shows a notably high level of global similarity. Overall, the quorum sensing genes seem to have diverged along with the Pseudomonadota phylum as a whole. This indicates that these quorum sensing systems are quite ancient, and arose very early in the Pseudomonadota lineage.<ref name="gray-2001">{{cite journal | vauthors = Gray KM, Garey JR | title = The evolution of bacterial LuxI and LuxR quorum sensing regulators | journal = Microbiology | volume = 147 | issue = Pt 8 | pages = 2379–2387 | date = August 2001 | pmid = 11496014 | doi = 10.1099/00221287-147-8-2379 | doi-access = free }}</ref><ref name="lerat-2004">{{cite journal | vauthors = Lerat E, Moran NA | title = The evolutionary history of quorum-sensing systems in bacteria | journal = Molecular Biology and Evolution | volume = 21 | issue = 5 | pages = 903–913 | date = May 2004 | pmid = 15014168 | doi = 10.1093/molbev/msh097 | doi-access = free }}</ref>

LuxI and LuxR have coevolved through a long history of horizontal gene transfer (HGT) events. An early study reconciling their gene trees with the rRNA tree suggested frequent HGT events for both LuxI and LuxR, indicating that they are horizontally transferred together and coevolve due to their functional dependency.<ref name="gray-2001" /> Similarly, in QS systems in bacteria associated with ''Populus deltoides'', the gene trees for ''luxI'' and ''luxR'' show high topological similarity, indicating coevolution of cognate pairs.<ref name=":9">{{Cite journal |last1=Schaefer |first1=Amy L. |last2=Lappala |first2=Colin R. |last3=Morlen |first3=Ryan P. |last4=Pelletier |first4=Dale A. |last5=Lu |first5=Tse-Yuan S. |last6=Lankford |first6=Patricia K. |last7=Harwood |first7=Caroline S. |last8=Greenberg |first8=E. Peter |date=2013-09-15 |title=LuxR- and LuxI-Type Quorum-Sensing Circuits Are Prevalent in Members of the Populus deltoides Microbiome |journal=Applied and Environmental Microbiology |language=en |volume=79 |issue=18 |pages=5745–5752 |doi=10.1128/AEM.01417-13 |issn=0099-2240 |pmc=3754149 |pmid=23851092|bibcode=2013ApEnM..79.5745S }}</ref> In addition to horizontal transfer of complete LuxI/LuxR-type QS systems, many Proteobacteria genomes exhibit an excess of LuxR genes or cases with only LuxR but not LuxI, acquired from different sources via HGT.<ref name=":9" /> Due to the frequent transfer of functional pairs of homologs (i.e., LuxI/LuxR-type systems from multiple independent sources), it is possible that the regulatory hierarchy formed by the LuxI/LuxR and RhlR-RhlI systems is a result of sequential integration of circuits obtained from different sources, due to interactions between multiple homologs.<ref name="gray-2001" /> Interestingly, LuxI genes have likely undergone horizontal gene transfer from Proteobacteria to other lineages, as they have been detected in Nitrospira lineage II.<ref>{{Cite journal |last1=Mellbye |first1=Brett L. |last2=Spieck |first2=Eva |last3=Bottomley |first3=Peter J. |last4=Sayavedra-Soto |first4=Luis A. |date=2017-11-15 |editor-last=Parales |editor-first=Rebecca E. |title=Acyl-Homoserine Lactone Production in Nitrifying Bacteria of the Genera Nitrosospira, Nitrobacter, and Nitrospira Identified via a Survey of Putative Quorum-Sensing Genes |journal=Applied and Environmental Microbiology |language=en |volume=83 |issue=22 |doi=10.1128/AEM.01540-17 |issn=0099-2240 |pmc=5666142 |pmid=28887424|bibcode=2017ApEnM..83E1540M }}</ref>

In quorum sensing genes of [[Gammaproteobacteria]], which includes ''[[Pseudomonas aeruginosa]]'' and ''[[Escherichia coli]]'', the LuxI/LuxR genes form a functional pair, with LuxI as the auto-inducer synthase and LuxR as the receptor. Gammaproteobacteria are unique in possessing quorum sensing genes, which, although functionally similar to the LuxI/LuxR genes, have a markedly divergent sequence.<ref name="lerat-2004"/> This family of quorum-sensing [[homology (biology)|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. In addition, species that employ multiple discrete quorum sensing systems are almost all members of the Gammaproteobacteria, and evidence of horizontal transfer of quorum sensing genes is most evident in this class.<ref name="gray-2001"/><ref name="lerat-2004"/>

====Interaction of quorum-sensing molecules with mammalian cells and its medical applications====
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. Quorum-sensing peptides have been demonstrated to interact with cancer cells, as well as to permeate the blood–brain barrier reaching the brain parenchyma.<ref>{{cite journal | vauthors = De Spiegeleer B, Verbeke F, D'Hondt M, Hendrix A, Van De Wiele C, Burvenich C, Peremans K, De Wever O, Bracke M, Wynendaele E | display-authors = 6 | title = The quorum sensing peptides PhrG, CSP and EDF promote angiogenesis and invasion of breast cancer cells in vitro | journal = PLOS ONE | volume = 10 | issue = 3 | pages = e0119471 | year = 2015 | pmid = 25780927 | pmc = 4363635 | doi = 10.1371/journal.pone.0119471 | bibcode = 2015PLoSO..1019471D | doi-access = free }}</ref><ref>{{cite journal | vauthors = Wynendaele E, Verbeke F, D'Hondt M, Hendrix A, Van De Wiele C, Burvenich C, Peremans K, De Wever O, Bracke M, De Spiegeleer B | display-authors = 6 | title = Crosstalk between the microbiome and cancer cells by quorum sensing peptides | journal = Peptides | volume = 64 | pages = 40–48 | date = February 2015 | pmid = 25559405 | doi = 10.1016/j.peptides.2014.12.009 | hdl-access = free | s2cid = 28064836 | hdl = 2263/59248 }}</ref><ref>{{cite journal | vauthors = Wynendaele E, Verbeke F, Stalmans S, Gevaert B, Janssens Y, Van De Wiele C, Peremans K, Burvenich C, De Spiegeleer B | display-authors = 6 | title = Quorum Sensing Peptides Selectively Penetrate the Blood-Brain Barrier | journal = PLOS ONE | volume = 10 | issue = 11 | pages = e0142071 | date = Nov 2015 | pmid = 26536593 | pmc = 4633044 | doi = 10.1371/journal.pone.0142071 | bibcode = 2015PLoSO..1042071W | doi-access = free }}</ref>

=== Role of quorum sensing in biofilm development ===
Quorum sensing (QS) is used by bacteria to form biofilms. Quorum sensing is used by bacteria to form biofilms because the process determines if the minimum number of bacteria necessary for biofilm formation are present. The criteria to form a biofilm is dependent on a certain density of bacteria rather than a certain number of bacteria being present. When aggregated in high enough densities, some bacteria may form biofilms to protect themselves from biotic or abiotic threats.<ref name=":5">{{Cite journal |last1=Bogino |first1=P |last2=de las Mercedes Oliva |first2=M |date=July 30, 2013 |title=The Role of Bacterial Biofilms and Surface Components in Plant-Bacterial Associations |journal=International Journal of Molecular Sciences |volume=14 |issue=8 |pages=15838–15859 |doi=10.3390/ijms140815838 |pmid=23903045 |pmc=3759889 |doi-access=free}}</ref> Quorum sensing is used by both Gram-positive and Gram-negative bacteria because it aids cellular reproduction. Once in a biofilm, bacteria can communicate with other bacteria of the same species. Bacteria can also communicate with other species of bacteria. This communication is enabled through autoinducers used by the bacteria.<ref name="Miller Bassler 2001">{{cite journal |last1=Miller |first1=Melissa B. |last2=Bassler |first2=Bonnie L. |title=Quorum Sensing in Bacteria |journal=Annual Review of Microbiology |date=October 2001 |volume=55 |issue=1 |pages=165–199 |doi=10.1146/annurev.micro.55.1.165 |pmid=11544353 }}</ref>

Additionally, certain responses can be generated by the host organism in response to the certain bacterial autoinducers. Despite the fact that specific bacterial quorum sensing systems are different, for example the target genes, signal relay mechanisms, and chemical signals used between bacteria, the ability to coordinate gene expression for a specific species of bacteria remains the same. This ability alludes to the larger idea that bacteria have potential to become a multicellular bacterial body.<ref name="Miller Bassler 2001"/>

Secondly, biofilms may also serve to transport nutrients into the microbial community or transport toxins out by means of channels that permeate the extracellular polymeric matrix (like cellulose) that holds the cells together. Finally, biofilms are an ideal environment for horizontal gene transfer through either conjugation or environmental DNA (eDNA) that exists in the biofilm matrix.<ref name=":5"/>

The process of biofilm development is often triggered by environmental signals, and bacteria are proven to require flagella to successfully approach a surface, adhere to it, and form the biofilm.<ref name=":5" /> As cells either replicate or aggregate in a location, the concentration of autoinducers outside of the cells increases until a critical mass threshold is reached. 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.<ref>{{cite news |last1=Windsor |first1=W. Jon |title=How Quorum Sensing Works |url=https://asm.org/Articles/2020/June/How-Quorum-Sensing-Works |work=American Society for Microbiology |date=12 June 2020 }}</ref>

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.<ref>{{Cite journal |last1=Jiang |first1=Qian |last2=Chen |first2=Jiashun |last3=Yang |first3=Chengbo |last4=Yin |first4=Yulong |last5=Yao |first5=Kang |date=2019-04-04 |title=Quorum Sensing: A Prospective Therapeutic Target for Bacterial Diseases |journal=BioMed Research International |language=en |volume=2019 |pages=e2015978 |doi=10.1155/2019/2015978 |doi-access=free |pmid=31080810 |pmc=6475571 |issn=2314-6133}}</ref>

==Archaea==

===Examples===

====''Methanosaeta harundinacea'' 6Ac====
''[[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.<ref name="Zhang-et-al-2012">{{cite journal | vauthors = Zhang G, Zhang F, Ding G, Li J, Guo X, Zhu J, Zhou L, Cai S, Liu X, Luo Y, Zhang G, Shi W, Dong X | display-authors = 6 | title = Acyl homoserine lactone-based quorum sensing in a methanogenic archaeon | journal = The ISME Journal | volume = 6 | issue = 7 | pages = 1336–1344 | date = July 2012 | pmid = 22237544 | pmc = 3379639 | doi = 10.1038/ismej.2011.203 | publisher = [[Springer Science+Business Media|Springer Science and Business Media LLC]] | doi-access = free | bibcode = 2012ISMEJ...6.1336Z }}</ref>

==Viruses==
A mechanism involving [[arbitrium]] has recently been described in bacteriophages infecting several ''[[Bacillus]]'' species.<ref name = EwenCallaway2017 >{{cite journal |last1=Callaway |first1=Ewen |title=Do you speak virus? Phages caught sending chemical messages |journal=Nature |date=18 January 2017 |doi=10.1038/nature.2017.21313 }}</ref><ref name=Tal1>Stokar-Avihail A, Tal N, Erez Z, Lopatina A, Sorek R. Widespread Utilization of Peptide Communication in Phages Infecting Soil and Pathogenic Bacteria. ''Cell host & microbe''. 2019 May 8;25(5):746-55.</ref> The viruses communicate with each other to ascertain their own density compared to potential hosts. They use this information to decide whether to enter a [[lytic]] or [[lysogenic]] life-cycle.<ref name="Erez2017">{{cite journal | vauthors = Erez Z, Steinberger-Levy I, Shamir M, Doron S, Stokar-Avihail A, Peleg Y, Melamed S, Leavitt A, Savidor A, Albeck S, Amitai G, Sorek R | display-authors = 6 | title = Communication between viruses guides lysis-lysogeny decisions | journal = Nature | volume = 541 | issue = 7638 | pages = 488–493 | date = January 2017 | pmid = 28099413 | pmc = 5378303 | doi = 10.1038/nature21049 | bibcode = 2017Natur.541..488E }}</ref> 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. This communication mechanism enables a coordinated infection strategy, significantly enhancing the efficiency of phage proliferation. By synchronizing their life cycles, bacteriophages can maximize their impact on the host population, potentially leading to more effective control of bacterial densities.

==Plants==
QS is important to plant-pathogen interactions, and their study has also contributed to the QS field more generally.<ref name="Pierson-et-al-1999" /><ref name="Bodman-et-al-2003" /> The first [[X-ray crystallography]] results for some of the key proteins were those of [[Pantoea stewartii subsp. stewartii|''Pantoea stewartii'' subsp. ''stewartii'']] in [[maize|maize/corn]]<ref name="Watson-et-al-2002" /><ref name="Bodman-et-al-2003" /> and ''[[Agrobacterium tumefaciens]]'', a [[crop pathogen]] with a wider range of hosts.<ref name="Vannini-et-al-2002" /><ref name="Zhang-et-al-2011" /><ref name="Bodman-et-al-2003" /> These interactions are facilitated by quorum-sensing molecules and play a major role in maintaining the pathogenicity of bacteria towards other hosts, such as humans. 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 model organism used is ''[[Arabidopsis thaliana]]''.<ref>{{cite journal | vauthors = Götz-Rösch C, Sieper T, Fekete A, Schmitt-Kopplin P, Hartmann A, Schröder P | title = Influence of bacterial N-acyl-homoserine lactones on growth parameters, pigments, antioxidative capacities and the xenobiotic phase II detoxification enzymes in barley and yam bean | journal = Frontiers in Plant Science | volume = 6 | pages = 205 | date = 2015-04-10 | pmid = 25914699 | pmc = 4392610 | doi = 10.3389/fpls.2015.00205 | doi-access = free }}</ref> Further insights reveal that AHLs influence plant immune responses and can alter plant hormone levels, thereby affecting plant growth and susceptibility to infection. Understanding these dynamics is crucial for developing innovative strategies to combat plant diseases and improve agricultural productivity. Researchers have also noted that certain plants can degrade these signaling molecules, potentially as a defensive strategy to disrupt bacterial communication. This interplay between bacterial signaling and plant responses suggests a complex co-evolutionary relationship that could be exploited to enhance crop resistance to bacterial pathogens.

The role of AHLs having long carbon-chains (C12, C14), which have an unknown receptor mechanism, is less well understood than AHLs having short carbon-chains (C4, C6, C8), which are perceived by the [[G protein-coupled receptor]]. A phenomenon called "AHL priming", which is a dependent signalling pathway, enhanced our knowledge of long-chain AHLs. The role of quorum-sensing molecules was better explained according to three categories: host physiology–based impact of quorum sensing molecules; ecological effects; and cellular signaling. Calcium signalling and [[calmodulin]] have a large role in short-chain AHLs' response in ''Arabidopsis''. Research was also conducted on [[barley]] and the crop called yam bean (''[[Pachyrhizus erosus]]'') that reveals the AHLs determining the detoxification enzymes called [[Glutathione S-transferase|GST]] were found less in yam bean.<ref>{{cite journal | vauthors = Hartmann A, Schikora A | title = Editorial: Plant responses to bacterial quorum sensing molecules | journal = Frontiers in Plant Science | volume = 6 | pages = 643 | date = 2015-08-19 | pmid = 26347761 | pmc = 4541025 | doi = 10.3389/fpls.2015.00643 | doi-access = free }}</ref>

Quorum sensing-based regulatory systems are necessary to plant-disease-causing bacteria. Looking towards developing new strategies based on plant-associated microbiomes, the aim of further study is to improve the quantity and quality of the food supply. Further research into this inter-kingdom communication also enhances the possibility of learning about quorum sensing in humans.<ref>{{cite journal | vauthors = Von Bodman SB, Bauer WD, Coplin DL | title = Quorum sensing in plant-pathogenic bacteria | journal = Annual Review of Phytopathology | volume = 41 | issue = 1 | pages = 455–482 | date = 2003-01-01 | pmid = 12730390 | doi = 10.1146/annurev.phyto.41.052002.095652 | s2cid = 3926735 }}</ref> This exploration could open new avenues for managing microbial communities in agricultural settings, potentially leading to the development of more sustainable farming practices that leverage natural microbial processes to boost crop resilience and productivity.

==Quorum quenching==

Quorum quenching is the process of preventing quorum sensing by disrupting signalling.<ref name=":12">{{cite journal | vauthors = Alagarasan G, Aswathy KS | title = Shoot the Message, Not the Messenger-Combating Pathogenic Virulence in Plants by Inhibiting Quorum Sensing Mediated Signaling Molecules | journal = Frontiers in Plant Science | volume = 8 | pages = 556 | year = 2017 | pmid = 28446917 | pmc = 5388769 | doi = 10.3389/fpls.2017.00556 | doi-access = free }}</ref> This is achieved by inactivating signalling enzymes, by introducing molecules that mimic signalling molecules and block their receptors, by degrading signalling molecules themselves, or by a modification of the quorum sensing signals due to an enzyme activity.<ref name=":3" /><ref name=":12" /><ref name=":22">{{cite journal | vauthors = Chan KG, Atkinson S, Mathee K, Sam CK, Chhabra SR, Cámara M, Koh CL, Williams P, Makar AB, McMartin KE, Palese M, Tephly TR, Glenn JK, Goldman J | display-authors = 6 | title = Task delegation to physician extenders--some comparisons | journal = American Journal of Public Health | volume = 66 | issue = 1 | pages = 64–66 | date = January 1976 | pmid = 21385437 <!-- |access-date=1 May 2022 --> | pmc = 3062576 | doi = 10.1186/1471-2180-11-51 | doi-access = free }}</ref><ref name="isolation3">{{cite journal | vauthors = Chan KG, Yin WF, Sam CK, Koh CL | title = A novel medium for the isolation of N-acylhomoserine lactone-degrading bacteria | journal = Journal of Industrial Microbiology & Biotechnology | volume = 36 | issue = 2 | pages = 247–251 | date = February 2009 | pmid = 18946694 | doi = 10.1007/s10295-008-0491-x | s2cid = 28637950 | doi-access = free }}</ref>

===Inhibition===

[[Closantel]] and [[triclosan]] are known inhibitors of quorum sensing enzymes.<ref name=":32">{{cite journal | vauthors = Basavaraju M, Sisnity VS, Palaparthy R, Addanki PK | title = Quorum quenching: Signal jamming in dental plaque biofilms | journal = Journal of Dental Sciences | volume = 11 | issue = 4 | pages = 349–352 | date = December 2016 | pmid = 30894996 | pmc = 6395279 | doi = 10.1016/j.jds.2016.02.002 }}</ref> Closantel induces aggregation of the [[histidine kinase]] sensor in two-component signalling. The latter disrupts the synthesis of a class of signalling molecules known as [[N-Acyl homoserine lactone|''N''-acyl homoserine lactones]] (AHLs) by blocking the [[Enoyl-acyl carrier protein reductase|enoyl-acyl carrier protein (ACP) reductase]].<ref name=":32" /><ref>{{cite journal | vauthors = Zhang LH, Dong YH | title = Quorum sensing and signal interference: diverse implications | journal = Molecular Microbiology | volume = 53 | issue = 6 | pages = 1563–1571 | date = September 2004 | pmid = 15341639 | doi = 10.1111/j.1365-2958.2004.04234.x | s2cid = 39018931 | doi-access = free }}</ref>

===Mimicry===

Two groups of well-known mimicking molecules include [[halogenated furanone]]s, which mimic AHL molecules, and synthetic Al peptides (AIPs), which mimic naturally occurring AIPs. These groups inhibit receptors from binding substrate or decrease the concentration of receptors in the cell.<ref name=":32" /> Furanones have also been found to act on AHL-dependant transcriptional activity, whereby the half life of the [[autoinducer]]-binding LuxR protein is significantly shortened.<ref>{{cite journal | vauthors = Manefield M, Rasmussen TB, Henzter M, Andersen JB, Steinberg P, Kjelleberg S, Givskov M | title = Halogenated furanones inhibit quorum sensing through accelerated LuxR turnover | journal = Microbiology | volume = 148 | issue = Pt 4 | pages = 1119–1127 | date = April 2002 | pmid = 11932456 | doi = 10.1099/00221287-148-4-1119 | doi-access = free }}</ref>

===Degradation===

Recently, a well-studied quorum quenching bacterial strain (KM1S) was isolated and its AHL degradation kinetics were studied using rapid resolution liquid [[chromatography]] (RRLC).<ref name="Rapid degradation3">{{cite journal | vauthors = Chan KG, Wong CS, Yin WF, Sam CK, Koh CL | title = Rapid degradation of N-3-oxo-acylhomoserine lactones by a Bacillus cereus isolate from Malaysian rainforest soil | journal = Antonie van Leeuwenhoek | volume = 98 | issue = 3 | pages = 299–305 | date = October 2010 | pmid = 20376561 | doi = 10.1007/s10482-010-9438-0 | s2cid = 12407347 }}</ref> RRLC efficiently separates components of a mixture to a high degree of sensitivity, based on their affinities for different liquid phases.<ref name=":52">{{cite journal | vauthors = Yoshida T, Majors RE | title = High-speed analyses using rapid resolution liquid chromatography on 1.8-microm porous particles | journal = Journal of Separation Science | volume = 29 | issue = 16 | pages = 2421–2432 | date = November 2006 | pmid = 17154122 | doi = 10.1002/jssc.200600267 }}</ref> It was found that the genome of this strain encoded an inactivation enzyme with distinct motifs targeting the degradation of AHLs.<ref name="Rapid degradation3" />

===Modifications===
As mentioned before, N-acyl-homoserine lactones (AHL) are the quorum sensing signaling molecules of the [[gram-negative bacteria]]. However, these molecules may have different functional groups on their acyl chain, and also a different length of acyl chain. Therefore, there exist many different AHL signaling molecules, for example, 3-oxododecanoyl-L-homoserine lactone (3OC12-HSL) or 3-hydroxydodecanoyl-L-homoserine lactone (3OHC12-HSL). The modification of those quorum sensing (QS) signaling molecules is another sort of quorum quenching. This can be carried out by an [[oxidoreductase]] activity.<ref name=":3" /> As an example, we will discuss the interaction between a host, ''[[Hydra vulgaris]]'', and the main colonizer of its epithelial cell surfaces, ''[[Curvibacter]]'' spp. Those bacteria produce 3-oxo-HSL quorum sensing molecules.<ref name=":3" /> However, the oxidoreductase activity of the polyp ''Hydra'' is able to modify the 3-oxo-HSL into their 3-hydroxy-HSL counterparts.<ref name=":3" /> We can characterize this as quorum quenching since there is an interference with quorum sensing molecules. 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. vulgaris''.<ref name=":3" />

===Applications===

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.<ref name=":42">{{cite journal | vauthors = Grandclément C, Tannières M, Moréra S, Dessaux Y, Faure D | title = Quorum quenching: role in nature and applied developments | journal = FEMS Microbiology Reviews | volume = 40 | issue = 1 | pages = 86–116 | date = January 2016 | pmid = 26432822 | doi = 10.1093/femsre/fuv038 | doi-access = free }}</ref> This technique has also been translated to agriculture, to restrict the spread of pathogenic bacteria that use quorum sensing in plants.<ref name=":42" /><ref>{{cite journal | vauthors = Galloway WR, Hodgkinson JT, Bowden S, Welch M, Spring DR | title = Applications of small molecule activators and inhibitors of quorum sensing in Gram-negative bacteria | journal = Trends in Microbiology | volume = 20 | issue = 9 | pages = 449–458 | date = September 2012 | pmid = 22771187 | doi = 10.1016/j.tim.2012.06.003 }}</ref> 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.<ref name=":42" /><ref name=":62">{{Cite journal| vauthors = Liu CX, Zhang DR, He Y, Zhao XS, Bai R |title=Modification of membrane surface for anti-biofouling performance: Effect of anti-adhesion and anti-bacteria approaches|journal=[[Journal of Membrane Science]]|volume=346|issue=1|pages=121–130|doi=10.1016/j.memsci.2009.09.028|year=2010}}</ref> Quorum quenching is recently studied for the control of fouling and emerging contaminants in electro membrane bioreactors (eMBRs) for the advanced treatment of wastewater.<ref name=":43">{{cite journal | vauthors = Borea L, Naddeo V, Belgiorno V, Choo KH | title = Control of quorum sensing signals and emerging contaminants in electrochemical membrane bioreactors | journal = Bioresource Technology | volume = 269 | pages = 89–95 | date = December 2018 | pmid = 30153550 | doi = 10.1016/j.biortech.2018.08.041 | bibcode = 2018BiTec.269...89B | s2cid = 52134789 }}</ref>  Extracts of several traditional medicinal herbs display quorum quenching activity, and have potential antibacterial applications.<ref>{{cite journal | vauthors = Moradi F, Hadi N | title = Quorum-quenching activity of some Iranian medicinal plants | journal = New Microbes and New Infections | volume = 42 | pages = 100882 | date = July 2021 | pmid = 34094582 | pmc = 8165558 | doi = 10.1016/j.nmni.2021.100882 }}</ref><ref>{{cite journal | vauthors = Moradi F, Hadi N, Bazargani A | title = Evaluation of quorum-sensing inhibitory effects of extracts of three traditional medicine plants with known antibacterial properties | journal = New Microbes and New Infections | volume = 38 | pages = 100769 | date = November 2020 | pmid = 33194208 | pmc = 7644747 | doi = 10.1016/j.nmni.2020.100769 }}</ref>

==Social insects==
Social insect colonies are an excellent example of a [[decentralized system]], because no individual is in charge of directing or making decisions for the colony. Several groups of social insects have been shown to use quorum sensing in a process that resembles collective decision-making.

===Examples===

====Ants====
Colonies of the ant ''[[Temnothorax albipennis]]'' nest in small crevices between rocks. When the rocks shift and the nest is broken up, these ants must quickly choose a new nest to move into. During the first phase of the decision-making process, a small portion of the workers leave the destroyed nest and search for new crevices. When one of these scout ants finds a potential nest, she assesses the quality of the crevice based on a variety of factors including the size of the interior, the number of openings (based on light level), and the presence or absence of dead ants.<ref>{{cite journal | vauthors = Franks NR, Dornhaus A, Metherell BG, Nelson TR, Lanfear SA, Symes WS | title = Not everything that counts can be counted: ants use multiple metrics for a single nest trait | journal = Proceedings. Biological Sciences | volume = 273 | issue = 1583 | pages = 165–169 | date = January 2006 | pmid = 16555783 | pmc = 1560019 | doi = 10.1098/rspb.2005.3312 }}</ref><ref>{{cite journal | vauthors = Franks NR, Hooper J, Webb C, Dornhaus A | title = Tomb evaders: house-hunting hygiene in ants | journal = Biology Letters | volume = 1 | issue = 2 | pages = 190–192 | date = June 2005 | pmid = 17148163 | pmc = 1626204 | doi = 10.1098/rsbl.2005.0302 }}</ref> The worker then returns to the destroyed nest, where she waits for a short period before recruiting other workers to follow her to the nest that she has found, using a process called [[tandem running]]. The waiting period is inversely related to the quality of the site; for instance, a worker that has found a poor site will wait longer than a worker that encountered a good site.<ref>{{cite journal | vauthors = Mallon EB, Pratt SC |title=Individual and collective decision-making during nest-site selection by the ant ''Leptothorax albipennis'' |journal=[[Behavioral Ecology and Sociobiology]] |volume=50 |issue=4 |pages=352–9 |year=2001 |doi=10.1007/s002650100377|bibcode=2001BEcoS..50..352M |s2cid=15360262 |display-authors=etal}}</ref> As the new recruits visit the potential nest site and make their own assessment of its quality, the number of ants visiting the crevice increases. During this stage, ants may be visiting many different potential nests. However, because of the differences in the waiting period, the number of ants in the best nest will tend to increase at the greatest rate. Eventually, the ants in this nest will sense that the rate at which they encounter other ants has exceeded a particular threshold, indicating that the quorum number has been reached.<ref>{{cite journal |author=Pratt, S.C. |title=Quorum sensing by encounter rates in the ant ''Temnothorax albipennis'' |journal=[[Behavioral Ecology (journal)|Behavioral Ecology]] |volume=16 |issue=2 |pages=488–96 |year=2005 |doi=10.1093/beheco/ari020|citeseerx=10.1.1.598.6340 }}</ref> Once the ants sense a quorum, they return to the destroyed nest and begin rapidly carrying the brood, queen, and fellow workers to the new nest. Scouts that are still tandem-running to other potential sites are also recruited to the new nest, and the entire colony moves. 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.

====Honey bees====
[[Honey bee]]s (''Apis mellifera'') also use quorum sensing to make decisions about new nest sites. Large colonies reproduce through a process called [[swarming (honeybee)|swarming]], in which the queen leaves the hive with a portion of the workers to form a new nest elsewhere. After leaving the nest, the workers form a swarm that hangs from a branch or overhanging structure. This swarm persists during the decision-making phase until a new nest site is chosen.

The quorum sensing process in honey bees is similar to the method used by ''[[Temnothorax]]'' ants in several ways. A small portion of the workers leave the swarm to search out new nest sites, and each worker assesses the quality of the cavity it finds. The worker then returns to the swarm and recruits other workers to her cavity using the honey bee [[waggle dance]]. However, instead of using a time delay, the number of dance repetitions the worker performs is dependent on the quality of the site. Workers that found poor nests stop dancing sooner, and can, therefore, be recruited to the better sites. 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. This vibration signal causes the swarm to take off and fly to the new nest location. In an experimental test, this decision-making process enabled honey bee swarms to choose the best nest site in four out of five trials.<ref>{{cite journal | vauthors = Seeley TD, Visscher PK |title=Group decision making in nest-site selection by honey bees |journal=[[Apidologie]] |volume=35 |issue=2 |pages=101–16 |year=2004 |doi=10.1051/apido:2004004|doi-access=free }}</ref><ref>{{cite journal | vauthors = Seeley TD, Visscher PK |title=Group decision making in honey bee swarms |journal=[[American Scientist]] |volume=94 |issue=3 |pages=220–9 |year=2006 |doi=10.1511/2006.3.220}}</ref>

==Synthetic biology==
Quorum sensing has been engineered using [[synthetic biological circuits]] in different systems. Examples include rewiring the AHL components to toxic genes to control population size in bacteria;<ref>{{cite journal | vauthors = You L, Cox RS, Weiss R, Arnold FH | title = Programmed population control by cell-cell communication and regulated killing | journal = Nature | volume = 428 | issue = 6985 | pages = 868–871 | date = April 2004 | pmid = 15064770 | doi = 10.1038/nature02491 | bibcode = 2004Natur.428..868Y | s2cid = 4426454 }}</ref> and constructing an auxin-based system to control population density in mammalian cells.<ref>{{cite journal | vauthors = Ma Y, Budde MW, Mayalu MN, Zhu J, Lu AC, Murray RM, Elowitz MB | title = Synthetic mammalian signaling circuits for robust cell population control | journal = Cell | volume = 185 | issue = 6 | pages = 967–979.e12 | date = March 2022 | pmid = 35235768 | doi = 10.1016/j.cell.2022.01.026|biorxiv=10.1101/2020.09.02.278564 | pmc = 8995209 | s2cid = 221510088 }}</ref> Synthetic quorum sensing circuits have been proposed to enable applications like controlling biofilms<ref>{{cite journal | vauthors = Hong SH, Hegde M, Kim J, Wang X, Jayaraman A, Wood TK | title = Synthetic quorum-sensing circuit to control consortial biofilm formation and dispersal in a microfluidic device | journal = Nature Communications | volume = 3 | issue = 1 | pages = 613 | date = January 2012 | pmid = 22215088 | pmc = 3272573 | doi = 10.1038/ncomms1616 | bibcode = 2012NatCo...3..613H | doi-access = free }}</ref> or enabling drug delivery.<ref>{{cite journal | vauthors = Din MO, Danino T, Prindle A, Skalak M, Selimkhanov J, Allen K, Julio E, Atolia E, Tsimring LS, Bhatia SN, Hasty J | display-authors = 6 | title = Synchronized cycles of bacterial lysis for in vivo delivery | journal = Nature | volume = 536 | issue = 7614 | pages = 81–85 | date = August 2016 | pmid = 27437587 | pmc = 5048415 | doi = 10.1038/nature18930 | bibcode = 2016Natur.536...81D }}</ref> Quorum sensing based genetic circuits have been used to convert AI-2 signals to AI-1 and then subsequently use the AI-1 signal to alter bacterial growth rate, thereby changing the composition of a consortium.<ref>{{cite journal | vauthors = Stephens K, Pozo M, Tsao CY, Hauk P, Bentley WE | title = Bacterial co-culture with cell signaling translator and growth controller modules for autonomously regulated culture composition | journal = Nature Communications | volume = 10 | issue = 1 | pages = 4129 | date = September 2019 | pmid = 31511505 | pmc = 6739400 | doi = 10.1038/s41467-019-12027-6 | bibcode = 2019NatCo..10.4129S }}</ref>

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.<ref name=":6">{{Cite journal |last=Bassler |first=Bonnie L |date=1999-12-01 |title=How bacteria talk to each other: regulation of gene expression by quorum sensing |url=https://www.sciencedirect.com/science/article/pii/S1369527499000259 |journal=Current Opinion in Microbiology |volume=2 |issue=6 |pages=582–587 |doi=10.1016/S1369-5274(99)00025-9 |pmid=10607620 |issn=1369-5274}}</ref> 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. It is also clear that intra- and inter-species cell–cell communication occurs and is regulated by quorum sensing systems. Further, there is mounting data demonstrating that autoinducer signals elicit specific responses from eukaryotic hosts.

==Computing and robotics==
Quorum sensing can be a useful tool for improving the function of self-organizing networks such as the SECOAS (Self-Organizing Collegiate Sensor) [[environmental monitoring]] system. In this system, individual nodes sense that there is a population of other nodes with similar data to report. The population then nominates just one node to report the data, resulting in power savings.<ref>{{cite conference |last1=Britton |first1=Matthew |last2=Sacks |first2=Lionel |title=The SECOAS Project: development of a self-organising, wireless sensor network for environmental monitoring |conference=International Workshop on Sensor and Actor Network Protocols and Applications |date=22 August 2004 |pages=1–7 |hdl=2440/66361 |url=http://www.cs.kent.ac.uk/projects/secoas/papers/SANPA-2004-Britton.pdf |url-status=dead |archive-url=https://web.archive.org/web/20081216223909/http://www.cs.kent.ac.uk/projects/secoas/papers/SANPA-2004-Britton.pdf |archive-date=2008-12-16 }}</ref> Ad hoc wireless networks can also benefit from quorum sensing, by allowing the system to detect and respond to network conditions.<ref>{{cite conference | vauthors = Peysakhov M, Regli W |book-title=Proceedings 2005 IEEE Swarm Intelligence Symposium, 2005. SIS 2005 |conference=Swarm Intelligence Symposium, Proceedings 2005 IEEE |year=2005 |pages=357–64 |title=Ant inspired server population management in a service-based computing environment |doi=10.1109/SIS.2005.1501643 |isbn=0-7803-8916-6}}</ref>

Quorum sensing can also be used to coordinate the behavior of autonomous robot swarms. Using a process similar to that used by ''Temnothorax'' ants, robots can make rapid group decisions without the direction of a controller.<ref>{{cite conference | vauthors = Sahin E, Franks N |title=Measurement of Space: From Ants to Robots |book-title=Proceedings of WGW 2002: EPSRC/BBSRC International Workshop |year= 2002 |citeseerx = 10.1.1.161.6407 }}</ref>

Despite recent advancements, the true nature of these back-and-forth conversations remains a mystery, and further rigorous research targeting inter- and intra- species communication is still necessary to maximize knowledge of quorum sensing and its potential to improve research and treatments of cancer and bacterial diseases. The code to understanding these complex bacterial languages is to decipher the impact of the words.<ref name=":6" />

== See also ==
{{col div|colwidth=30em}}
* [[Cell signaling]]
* [[Collective behavior]]
* [[Diffusible signal factor]]
* [[Interspecies quorum sensing]]
* [[Microbial intelligence]]
* [[Pheromone]]
* [[Signal transduction]]
* [[Swarm intelligence]]
{{colend}}

== References ==
{{Reflist|2|refs=

<ref name="Nealson-1977">{{cite journal | vauthors = Nealson KH | title = Autoinduction of bacterial luciferase. Occurrence, mechanism and significance | journal = Archives of Microbiology | volume = 112 | issue = 1 | pages = 73–79 | date = February 1977 | pmid = 843170 | doi = 10.1007/bf00446657 | publisher = [[Springer Science+Business Media|Springer Science and Business Media LLC]] | bibcode = 1977ArMic.112...73N | s2cid = 34239721 }}</ref>

<ref name="Bodman-et-al-2003">{{cite journal | vauthors = Von Bodman SB, Bauer WD, Coplin DL | title = Quorum sensing in plant-pathogenic bacteria | journal = Annual Review of Phytopathology | volume = 41 | issue = 1 | pages = 455–482 | year = 2003 | pmid = 12730390 | doi = 10.1146/annurev.phyto.41.052002.095652 | publisher = [[Annual Reviews (publisher)|Annual Reviews]] | s2cid = 3926735 }}</ref>

<ref name="Pierson-et-al-1999">{{cite book | veditors = Dunny G, Winans S | title=Cell-cell signaling in bacteria | publisher=[[American Society for Microbiology]] Press | publication-place=[[Washington, D.C.]] | year=1999 | isbn=978-1-55581-149-5 | oclc=40075829 | vauthors = Pierson III LS, Wood DW, Beck von Bodman S | chapter=Quorum sensing in other plant-associated bacteria | pages=101–15 }}</ref>

<ref name="Watson-et-al-2002">{{cite journal | vauthors = Watson WT, Minogue TD, Val DL, von Bodman SB, Churchill ME | title = Structural basis and specificity of acyl-homoserine lactone signal production in bacterial quorum sensing | journal = Molecular Cell | volume = 9 | issue = 3 | pages = 685–694 | date = March 2002 | pmid = 11931774 | doi = 10.1016/s1097-2765(02)00480-x | publisher = [[Elsevier]] BV | doi-access = free }}</ref>

<ref name="Vannini-et-al-2002">{{cite journal | vauthors = Vannini A, Volpari C, Gargioli C, Muraglia E, Cortese R, De Francesco R, Neddermann P, Marco SD | display-authors = 6 | title = The crystal structure of the quorum sensing protein TraR bound to its autoinducer and target DNA | journal = The EMBO Journal | volume = 21 | issue = 17 | pages = 4393–4401 | date = September 2002 | pmid = 12198141 | pmc = 126196 | doi = 10.1093/emboj/cdf459 | publisher = [[Wiley Publishing]] }}</ref>

<ref name="Zhang-et-al-2011">{{cite journal | vauthors = Zhang RG, Pappas KM, Pappas T, Brace JL, Miller PC, Oulmassov T, Molyneaux JM, Anderson JC, Bashkin JK, Winans SC, Joachimiak A | display-authors = 6 | title = Structure of a bacterial quorum-sensing transcription factor complexed with pheromone and DNA | journal = Nature | volume = 417 | issue = 6892 | pages = 971–974 | date = June 2002 | pmid = 12087407 | doi = 10.1038/nature10294 | publisher = [[Springer Science+Business Media|Springer Science and Business Media LLC]] | doi-access = free }}</ref>

<ref name="Lupp-et-al-2003">{{cite journal | vauthors = Lupp C, Urbanowski M, Greenberg EP, Ruby EG | title = The Vibrio fischeri quorum-sensing systems ain and lux sequentially induce luminescence gene expression and are important for persistence in the squid host | journal = Molecular Microbiology | volume = 50 | issue = 1 | pages = 319–331 | date = October 2003 | pmid = 14507383 | doi = 10.1046/j.1365-2958.2003.t01-1-03585.x | publisher = [[Wiley Publishing]] | doi-access = free }}</ref>

}}

== Further reading ==
* [http://rstb.royalsocietypublishing.org/content/362/1483 Dedicated issue of ''Philosophical Transactions B'' on quorum sensing] (2007). Some articles are freely available.
* High citation review: {{cite journal | vauthors = Waters CM, Bassler BL | title = Quorum sensing: cell-to-cell communication in bacteria | journal = Annual Review of Cell and Developmental Biology | volume = 21 | pages = 319–346 | year = 2005 | pmid = 16212498 | doi = 10.1146/annurev.cellbio.21.012704.131001 }}

== External links ==
* [http://www.nottingham.ac.uk/quorum The Quorum Sensing Website]
* [http://www.hhmi.org/research/investigators/bassler.html Cell-to-Cell Communication in Bacteria] {{Webarchive|url=https://web.archive.org/web/20130517045243/http://www.hhmi.org/research/investigators/bassler.html |date=2013-05-17 }}
* [https://web.archive.org/web/20081216223909/http://www.cs.kent.ac.uk/projects/secoas/papers/SANPA-2004-Britton.pdf The SECOAS project—Development of a Self-Organising, Wireless Sensor Network for Environmental Monitoring]
* [https://web.archive.org/web/20080907022141/http://www.media.mit.edu/resenv/classes/MAS965/readings/SwarmBots.pdf Measurement of Space: From Ants to Robots]
* [http://www.rsc.org/Publishing/Journals/cb/Volume/2008/6/Communicating_with_nature.asp Instant insight] into quorum sensing from the [[Royal Society of Chemistry]]
* [http://www.ted.com/index.php/talks/bonnie_bassler_on_how_bacteria_communicate.html Bonnie Bassler: Discovering bacteria's amazing communication system] {{Webarchive|url=https://web.archive.org/web/20111205033015/http://www.ted.com/index.php/talks/bonnie_bassler_on_how_bacteria_communicate.html |date=2011-12-05 }}
*[https://www.ibiology.org/microbiology/quorum-sensing/ Bonnie Bassler's seminar: "Cell-Cell Communication in Bacteria"]

{{Cell signaling}}
{{swarming}}
{{Microorganisms}}

{{DEFAULTSORT:Quorum Sensing}}
[[Category:Bacteriology]]
[[Category:Microbial population biology]]
[[Category:Cell communication]]
[[Category:Complex systems theory]]
[[Category:Superorganisms]]
[[Category:Environmental microbiology]]
[[Category:Gene expression]]