Editing Quorum sensing (section)

==== ''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>