Solo acylhomoserine lactone synthase from predatory myxobacterium suggests beneficial participation in interspecies cross talk

The prototypical intraspecies quorum signaling systems mediated by acylhomoserine lactones are abundant in proteobacteria, and considerable efforts have provided insight into the regulated physiological features impacted by such systems. However, the high occurrence of orphaned AHL receptors present in bacterial species that do not produce cognate AHL signals suggests the involvement of AHL signals in interspecies interactions within polymicrobial communities. The specific benefits of these interactions are mostly unknown. Considered a key taxon in microbial communities, myxobacteria exist as coordinated swarms that utilize an excreted combination of lytic enzymes and specialized metabolites to facilitate predation of numerous microbial phyla. Of all the biosynthetic gene clusters associated with myxobacteria deposited in the antiSMASH database, only one putative acylhomoserine lactone synthase, agpI, was observed in genome data from the myxobacterium Archangium gephyra. Without a cognate AHL receptor, we consider AgpI an orphaned AHL synthase. Herein we report the bioinformatic assessment of AgpI and discovery of a second myxobacterial AHL synthase from Vitiosangium sp. strain GDMCC 1.1324. Heterologous expression of each synthase in Escherichia coli provided detectible quantities of 3 AHL signals including 2 known AHLs, C8-AHL and C9-AHL. The functional, orphaned AHL synthase, AgpI, from the predatory myxobacterium A. gephyra provides unique support for beneficial interspecies crosstalk within polymicrobial communities.