Quorum sensing in Gram-negative bacteria: Small-molecule modulation of AHL and AI-2 quorum sensing pathways

Numerous species of bacteria employ a mechanism of intercellular communication known as quorum sensing. AHLs are the most common class of autoinducer used by Gram-negative bacteria; indeed quorum sensing mediated by AHLs represents one of the best-understood bacterial systems at the molecular level. In addition, all small molecules can be used in a conditional manner; that is, they are added at any time point in the experiment, allowing for temporal control of a biological system. Homologues of LuxI and LuxR have been identified in a large number of bacterial genomes with a variety of different AHLs regulating a range of physiological functions. In general, each bacterial species responds specifically to its own unique AHL autoinducer; the same general structure is maintained, but the length and functionality of the acyl chain vary. This orphan receptor, termed QscR has been shown to play a regulatory role within the larger AHL quorum sensing network of this bacterium, including the control of virulence.