Bacterial gene regulation by α-hydroxyketone signaling

Bacteria produce diffusible, small signaling molecules termed autoinducers to promote cell–cell communication. Recently, a novel class of signaling molecules, the α-hydroxyketones (AHKs), was discovered in the facultative human pathogens Legionella pneumophila and Vibrio cholerae. In this review, we summarize and compare findings on AHK signaling in these bacteria. The L. pneumophila lqs (Legionella quorum sensing) and V. cholerae cqs (cholera quorum sensing) gene clusters synthesize and detect Legionella autoinducer 1 (3-hydroxypentadecan-4-one) or cholera autoinducer-1 (3-hydroxytridecan-4-one), respectively. In addition to the autoinducer synthase and cognate sensor kinase encoded in the cqs locus, the lqs cluster also harbors a prototypic response regulator. AHK signaling regulates pathogen–host cell interactions, bacterial virulence, formation of biofilms or extracellular filaments, and expression of a genomic island. The lqs/cqs gene cluster is present in several environmental bacteria, suggesting that AHKs are widely used for cell–cell signaling.