Molecular basis of quorum sensing signal-response systems in bacteria

Bacteria use quorum sensing (QS) to conduct gene expression programmes connected with collective behaviors. QS indicates on the capacity of bacteria to monitor their population density and regulate gene expression. QS activates from tens to hundreds of genes that underlie different biological processes. The QS-regulated processes organize horizontal gene transfer, the formation of biofilms, multicellular behaviors, microbe–host and microbe–microbe relations. The QS signaling requires the production, release, detection, exchange and perception of bacterial compounds, known as autoinducers or QS signals. Recently, new autoinducers have been discovered in bacteria and it has been shown how these molecules are recognized by the respective receptors. Autoinducers belong to three major classes: acyl-homoserine lactones (AHLs) used by Gram-negative bacteria, specific oligopeptides used by Gram-positive bacteria and universal autoinducers. The aim of this paper is to provide an overview of molecular basis of the QS phenomenon, characterization of intra- and interspecies QS signaling molecules and biological processes regulated by these molecules.