Characterization of Bacillus stercoris JK-6 as an Antifungal Agent Against Crop Fungal Diseases

Biological control is one of the most effective strategies for managing crop fungal diseases such as rice blast, which severely threatens global food security. However, the limited availability of microbial biocontrol resources and incomplete understanding of their mechanisms hinder the development of practical biocontrol technologies for rice blast. In this study, a Bacillus stercoris strain, JK-6, isolated from the rhizosphere soil of rice, was identified as a promising biocontrol agent with strong antagonistic activity against multiple fungal pathogens. The fermentation broth of JK-6 yielded inhibition rates of 94.96% against Magnaporthe oryzae (rice blast), 75.83% against Bipolaris maydis (maize southern leaf blight), and 70.46% against Fusarium graminearum (wheat head blight). Whole-genome sequencing of JK-6 revealed 12 biosynthetic gene clusters, one of which was responsible for the biosynthesis of the lipopeptide surfactin. Further assays showed that 200 μM surfactin exhibited broad-spectrum antifungal activity, with inhibition rates of 82.90%, 66.76%, and 52.54% against M. oryzae, B. maydis, and F. graminearum, respectively. Mechanistically, surfactin suppresses fungal growth by downregulating genes involved in integral and intrinsic membrane components and oxygen transport, as validated by transcriptomic analysis. Our discoveries not only advance the conceptual understanding of the surfactin-mediated JK-6 antagonistic activity against fungal diseases but also offer an effective new approach for the practical control of crop fungal diseases.