Exploiting a global regulator for small molecule discovery in Photorhabdus luminescens.

Bacterially produced small molecules demonstrate a remarkable range of structural and functional diversity and include some of our most useful biological probes and therapeutic agents. Annotations of bacterial genomes reveal a large gap between the number of known small molecules and the number of biosynthetic genes/loci that could produce such small molecules, a gap that most likely originates from tight regulatory control by the producing organism. This study coupled a global transcriptional regulator, HexA, to secondary metabolite production in Photorhabdus luminescens, a member of the Gammaproteobacteria that participates in a complex symbiosis with nematode worms and insect larvae. HexA is a LysR-type transcriptional repressor, and knocking it out to create a P. luminescens DeltahexA mutant led to dramatic upregulation of biosynthesized small molecules. Use of this mutant expanded a family of stilbene-derived small molecules, which were known to play important roles in the symbiosis, from three members to at least nine members.