Bacterial Communication Systems

Like multicellular organisms, bacteria can regulate gene expression at the multicellular level. The coordination of multicellular bacterial behavior occurs via a chemically mediated process known as quorum sensing (QS). Currently, there are five well-defined classes of chemical signals in bacteria that support the concept of QS. By coupling an extracellular bacterial signal with gene expression, bacteria can control gene expression in such a way that the majority of the population expresses the same phenotype simultaneously. In this chapter, the molecular mechanisms of QS, the effective range of QS-regulated processes, and the ecological role of quorum quenching, namely the inhibition of QS, are discussed. QS occurs most frequently in bacterial species that associate with surfaces or higher organisms, either as a pathogen or as a beneficial associate. Three seminal examples of QS-mediated cross-kingdom signaling in the marine environment are reviewed: (i) the chemical defense of the red seaweed Delisea pulchra; (ii) the mutualistic association of Vibrio fischeri with the Hawaiian bobtail squid; and (iii) the exploitation of bacterial QS during settlement of marine spores and invertebrate larvae.