Multi-omic investigation identifies key antifungal biochemistry during fermentation of a Streptomyces biological control agent.

The use of multi-omic approaches has significantly advanced the exploration of microbial traits, leading to the discovery of new bioactive compounds and their mechanisms of action. Streptomyces sp. MH71 is known for its antifungal properties with potential for use in crop protection. Using genomic, transcriptomic, and metabolomic analyses, the antifungal metabolic capacity of Streptomyces sp. MH71 was investigated. After 96 hours of liquid fermentation, cell-free spent media showed inhibitory activity against the fungal phytopathogen Verticillium dahliae, with the lowest IC value being 0.11 % (v/v) after 144 h. Through whole-genome sequencing, we obtained a near-complete genome of 11 Mb with a G+C content of 71 % for Streptomyces sp. MH71. Genome mining identified 50 putative biosynthetic gene clusters, six of which produced known antimicrobial compounds. To link antifungal activity with candidate biosynthetic pathways, a transcriptomic approach was applied to understand antifungal induction in MH71 cells during the observed increase in antifungal activity. This approach revealed 2774 genes that exhibited differential expression, with significant upregulation of genes involved in biosynthesis of secondary metabolites during the stationary growth phase. Metabolomic analyses using LC-MS and GC-MS of secreted compounds identified a cocktail of potent antifungal metabolites, including volatiles with antifungal activity. By combining genome mining, bioactivity data, transcriptomics, and metabolomics, we describe in detail the gene expression and metabolite products driving antifungal activity during microbial fermentation.