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

Abstract

Many species ofProteobacteriaproduce 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 ofProsthecomicrobium hirschii, a dimorphic prosthecate bacterium, possesses aluxI-like AHL synthase gene that we predicted to encode a CoA-utilizing enzyme. We show theP. hirschiiLuxI homolog catalyzes synthesis of phenylacetyl-homoserine lactone (PA-HSL). Our experiments showP. hirschiiobtains 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 inP. hirschii. 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.