Recent advances in biology: intercellular communication and quorum sensing in micro-organisms

N-acyl-L-homoserine lactones are involved as intercellular signalling agents controlling a wide range of physiological responses in Gram-negative bacteria. They function especially in vibrios, pseudomonads and erwinias as well as in Rhizobium and Agrobacterium spp, particularly where the bacteria are in symbiotic or parasitic relationships with higher organisms. Several Gram-negatives, such as Escherichia coli, do not, however, appear to produce or respond to AHLs and they may have other intercellular signalling molecules. The present review reports that several stress related responses in E. coli can be induced by supernatant fluids from cultures which have already induced the response. In some cases at least, the active agents in the supernatant fluids are proteins rather than AHLs.