Quorum sensing and the cell-cell communication dependent regulation of gene expression in pathogenic and non-pathogenic bacteria

Although it has been clear for some time that individual bacterial cells em ploy intra-cellular signalling systems to sense, integrate and process info rmation from their surroundings, their widespread capacity to perceive info rmation from other bacterial cells is only just beginning to be recognised. Recent work has established that diverse bacteria exploit a cell-cell comm unication device to regulate the transcription of multiple target genes. Th is communication device termed 'quorum sensing', depends on the production of one or more diffusible signal molecules termed 'autoinducers' or 'pherom ones' which enable a bacterium to monitor its own cell population density. Quorum sensing is thus an example of multicellular behaviour in prokaryotes and regulates diverse physiological processes including bioluminescence, s warming, antibiotic biosynthesis, plasmid conjugal transfer and the product ion of virulence determinants in animal, fish and plant pathogens. In Gram- negative bacteria, the best understood family of signal molecules are the N -acylhomoserine lactones (AHLs) which vary predominantly in the presence or absence of an acyl chain C3 substituent (oxo- or hydroxy-) and length of t he N-acyl side chain. However not all quorum sensing signal molecules are A HLs; in Gram-positive bacteria, they are often post-translationally modifie d peptides. irrespective of the chemical 'language' employed, interference with either the synthesis or transmission of a quorum sensing signal molecu le in pathogenic bacteria offers an exciting new strategy for controlling i nfection.