1. Department of Microbiology, University of Washington, Washington 98195, USA
2. Molecular Pharmacology and Cancer Therapeutics Program, Roswell Park Cancer Institute, State University of New York at Buffalo, Buffalo, New York 14263, USA
3. Danisco Genencor, Palo Alto, California 94304, USA
4. Institute of Molecular Biosciences, University of Frankfurt, Frankfurt 60438, Germany

Correspondence to: Caroline S. Harwood¹ Correspondence and requests for materials should be addressed to C.S.H. (Email: csh5@u.washington.edu).

Abstract

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.

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