Genome mining and heterologous expression reveal two distinct families of lasso peptides highly conserved in endofungal bacteria.
Genome mining identified the fungal-bacterial endosymbiosis Rhizopus microsporus-Mycetohabitans (previously: Burkholderia) rhizoxinica as a rich source of novel natural products. Yet, most of the predicted compounds have remained cryptic. In this study we employed heterologous expression to isolate and characterize three ribosomally-synthesized and post-translationally modified peptides (RiPPs) with lariat topology (lasso peptides) from the endosymbiont M. rhizoxinica: burhizin-23, mycetohabin-16 and mycetohabin-15. Through coexpression experiments it was shown that an orphan gene product results in mature mycetohabin-15, albeit encoded remotely from the core biosynthetic gene cluster. Comparative genomics revealed that mycetohabins are highly conserved trait among M. rhizoxinica and related endosymbiotic bacteria. Gene knockout and reinfection experiments indicated that the lasso peptides are not crucial for establishing the symbiosis; instead, the peptides are exported into the environment during endosymbiosis. This is the first report on lasso peptides from endosymbiontic bacteria.