Editing Quorum sensing (section)

===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" />