Bacillus velezensis 802 with antagonistic activity against Aspergillus flavus: genome characterization, secondary metabolites and antifungal mechanism.

BACKGROUND

Aspergillus flavus causes severs postharvest spoilage and aflatoxins contamination of agricultural commodities, posing major threats to food safety and human health and underscoring the need for safe, effective biocontrol strategies. This study aimed to identify an antagonistic endophytic bacterium against A. flavus and to integrate whole-genome mining, metabolomics, and mechanistic assays to elucidate the molecular basis of its antifungal activity.

METHODS

An endophytic isolate was identified as Bacillus velezensis 802. Its crude extract was evaluated in vitro, and SEM, CLSM, and physiological assays were used to assess hyphal morphology, membrane integrity, mitochondrial function, energy metabolism, and apoptosis. Bioinformatic analysis of the whole-genome sequence was used to predict biosynthetic gene clusters (BGCs) and their associated pathways. UHPLC-MS/MS was used to identify metabolites in the active extract.

RESULTS

Bacillus velezensis 802 inhibited A. flavus by 70.16%. The crude extract induced hyphal wrinkling and swelling, disrupted membrane integrity, reduced mitochondrial membrane potential, suppressed key energy-metabolism enzymes, and activated the Caspase-9-mediated apoptotic pathway. Genome analysis revealed a 3,951,806 bp circular chromosome containing 13 BGCs. Metabolomics identified six secondary metabolites, among which isobutyric acid showed the strongest antifungal activity.

CONCLUSION

By coupling whole-genome mining with metabolomic profiling and mechanistic validation, this study demonstrates that B. velezensis 802 suppresses A. flavus through multi-target interference with cell structure, energy metabolism, and apoptosis. The strain and its metabolites, especially isobutyric acid, are promising biocontrol candidates for improving grain storage safety.