An aryl-homoserine lactone quorum-sensing signal produced by a dimorphic prosthecate bacterium.

Abstract

Many species of <i>Proteobacteria</i> produce acyl-homoserine lactone (AHL) compounds as quorum-sensing (QS) signals for cell density-dependent gene regulation. Most known AHL synthases, LuxI-type enzymes, produce fatty AHLs, and the fatty acid moiety is derived from an acyl-acyl carrier protein (ACP) intermediate in fatty acid biosynthesis. Recently, a class of LuxI homologs has been shown to use CoA-linked aromatic or amino acid substrates for AHL synthesis. By using an informatics approach, we found the CoA class of LuxI homologs exists primarily in α-Proteobacteria. The genome of <i>Prosthecomicrobium hirschii</i>, a dimorphic prosthecate bacterium, possesses a <i>luxI-</i>like AHL synthase gene that we predicted to encode a CoA-utilizing enzyme. We show the <i>P. hirschii</i> LuxI homolog catalyzes synthesis of phenylacetyl-homoserine lactone (PA-HSL). Our experiments show <i>P. hirschii</i> obtains phenylacetate from its environment and uses a CoA ligase to produce the phenylacetyl-CoA substrate for the LuxI homolog. By using an AHL degrading enzyme, we showed that PA-HSL controls aggregation, biofilm formation, and pigment production in <i>P. hirschii</i> These findings advance a limited understanding of the CoA-dependent AHL synthases. We describe how to identify putative members of the class, we describe a signal synthesized by using an environmental aromatic acid, and we identify phenotypes controlled by the aryl-HSL.