Genome-led discovery of novel microbial natural products

Microorganisms have been increasingly exploited for their remarkable ability to produce diverse natural products, which display bioactivities ranging from antimicrobial and anticancer to signalling and developmental. Genome sequencing has revealed that bacteria harbour many more biosynthetic gene clusters (BGCs) for natural products than are currently characterised. Whilst several genome mining tools have been developed to aid discovery, some classes of BGCs remain difficult to identify. One such class is ribosomally-synthesised and post-translationally modified peptides (RiPPs). RiPP BGCs are small with few regions of homology, and the short precursor peptides are rarely annotated in genomes. After developing a targeted genome mining approach for RiPPs, we identified a novel family of BGCs spanning over 200 actinobacterial genomes. The presence of diverse biosynthetic enzymes and sequence variation of the precursor peptides suggest that these BGCs may produce several structurally diverse molecules. We have successfully TAR cloned one such BGC from Streptomycesand expressed it heterologously, and metabolomic analysis led to identification of the pathway product. Gene deletion experiments have also confirmed the involvement of individual biosynthetic enzymes. The compound has been purified and the structure elucidated by NMR. Further work will focus on exploring RiPP BGCs from other species and investigating the biological role of these molecules. The discovery of such a diverse and highly conserved group of BGCs highlights that we are still scratching the surface of the huge biosynthetic capacity of microorganisms, and the use of more sophisticated genome mining tools could help unveil many more important molecules in the future.