A new class of homoserine lactone quorum-sensing signals

Quorum sensing is a term used to describe cell-to-cell communication that allows cell-density-dependent gene expression. Many bacteria use acyl-homoserine lactone (acyl-HSL) synthases to generate fatty acyl-HSL quorum-sensing signals, which function with signal receptors to control expression of specific genes. The fatty acyl group is derived from fatty acid biosynthesis and provides signal specificity, but the variety of signals is limited. Here we show that the photosynthetic bacterium Rhodopseudomonas palustris uses an acyl-HSL synthase to produce p -coumaroyl-HSL by using environmental p -coumaric acid rather than fatty acids from cellular pools. The bacterium has a signal receptor with homology to fatty acyl-HSL receptors that responds to p -coumaroyl-HSL to regulate global gene expression. We also found that p -coumaroyl-HSL is made by other bacteria including Bradyrhizobium sp. and Silicibacter pomeroyi . This discovery extends the range of possibilities for acyl-HSL quorum sensing and raises fundamental questions about quorum sensing within the context of environmental signalling. Bacterial chit-chat Many bacteria use quorum sensing as a means of cell-to-cell communication, allowing population-dependent control of gene expression. The signal molecules involved are usually acyl-homoserine lactones (acyl-HSLs), incorporating fatty acid groups to provide specificity via a series of different signal receptors acting on subsets of genes. Only a few such signals are known so far, but the discovery of a new variation on the HSL theme in the photosynthetic bacterium Rhodopseudomonas palustris suggests that many more such signals might exist. The bacterium uses an enzyme similar to fatty acyl-HSL synthase to produce p -coumaroyl-HSL from environmental p -coumaric acid rather than using fatty acids from cellular pools. The bacterium has a signal receptor that responds to p -coumaroyl-HSL to regulate global gene expression. Other bacterial species also make p -coumaroyl-HSL, raising the possibility of intraspecies communication in an environmental context. Acyl-homoserine lactone (AHL) quorum sensing allows population-dependent control of gene expression in numerous bacterial species. Many AHL quorum-sensing systems are known, all of which use fatty acid groups to provide AHL specificity. This paper reports the discovery that some bacteria make a non-fatty AHL by using enzymes related to the fatty AHL synthase pathway, thus greatly expanding the realm of sign