Occidiofungin Is the Key Metabolite for Antifungal Activity of the Endophytic Bacterium sp. MS455 Against .

Aflatoxin is a secondary metabolite produced by fungi and presents a major food safety concern globally. Among the available methods for prevention and control of aflatoxin, the application of antifungal bacteria has gained favor in recent years. An endophytic bacterium MS455, isolated from soybean, exhibited broad-spectrum antifungal activity against economically important pathogens, including . MS455 was identified as a strain of based on genomic analysis. Random and site-specific mutations were used in discovery of the genes that share high homology to the gene cluster of strain MS14, which is responsible for production of the antifungal compound occidiofungin. RNA sequencing analysis demonstrated that , a homolog to the LuxR-type regulatory gene, regulates occidiofungin biosynthesis in MS455. Additionally, 284 differentially expressed genes, including 138 upregulated and 146 downregulated genes, suggesting that, in addition to its role in occidiofungin production, is involved in expression of multiple genes, especially those involved in ornibactin biosynthesis. Plate bioassays showed the growth of was significantly inhibited by the wild-type strain MS455 as compared with the mutant. Similarly, corn kernel assays showed that growth of and aflatoxin production were reduced significantly by MS455 as compared with buffer control and the mutant. Collectively, the results demonstrated that production of occidiofungin is essential for antifungal activity of the endophytic bacterium MS455. This research has provided insights about antifungal mechanisms of MS455 and development of biological approaches to prevent aflatoxin contamination in plant production.