N-Acyl homoserine lactone
N-Acyl homoserine lactones (Abbreviated as AHLs or N-AHLs) are a class of signaling molecules involved in bacterial quorum sensing. Quorum sensing is a method of communication between bacteria that enables the coordination of group-based behavior based on population density. They signal changes in gene expression, such as switching between the flagella gene and the gene for pili for the development of a biofilm.
In bacterial signalling, N-AHLs are produced within the bacterial cell and released into the environment. N-AHLs produced by different bacteria differ in the length of the R-group side-chain. Chain lengths vary from 4 to 18 carbon atoms and in the substitution of a carbonyl at the third carbon.
Homoserine lactone is also a product of the proteolytic reaction of cyanogen bromide (CNBR) with a methionine residue in a protein. This reaction is important for chemical sequencing of proteins, as the Edman degradation process is unable to sequence more than 70 consecutive residues.
The production signaling molecules are produced within the cell and are released into the environment. The resulting concentration of signaling molecules in the environment is dependent upon population density. Once the population density has reached a particular threshold, gene expression can begin. This allows bacteria to coordinate group-based behavior. It has also been suggested that N-AHLs alter local surface tension enough to create Marangoni flows which facilitate swarming and colony motility. 
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