Multi-Pathway Antifungal Mechanism of Marine-Derived Bacillus sp. BAF143 Against Aspergillus flavus

Aspergillus flavus is a major fungal pathogen that causes postharvest spoilage and carcinogenic aflatoxin contamination in agricultural commodities, necessitating the development of novel biocontrol strategies. In this study, a bacterial strain of Bacillus sp. BAF143, isolated from a Martin medium plate used for marine fungal cultivation, exhibited potent antifungal activity against A. flavus. The crude extract of BAF143 demonstrated strong inhibition of mycelial growth (62.36 ± 1.00%) and spore germination (90.10 ± 0.21%). Transcriptomic analysis revealed a distinctive response pattern: genes involved in ribosome biogenesis, oxidative phosphorylation, ergosterol biosynthesis, cell cycle, DNA replication, and energy metabolism were significantly upregulated, whereas cell wall synthesis and MAPK signaling pathway genes were downregulated. This paradoxical transcriptional landscape indicates that A. flavus mounted a desperate compensatory response to counteract cellular damage, which was ultimately overwhelmed by excessive reactive oxygen species accumulation, lipid peroxidation, and mitochondrial dysfunction. Physiological assays confirmed membrane integrity loss, mitochondrial membrane potential collapse, and DNA fragmentation, leading to apoptosis-like cell death. On peanuts, the crude extract achieved a 96.18% reduction in A. flavus spore count after 21 days with sustained protection. These findings demonstrate that the BAF143 crude extract exerts a multi-pathway antifungal mechanism, positioning Bacillus sp. BAF143 as a promising biocontrol agent for mitigating A. flavus contamination and aflatoxin risks in postharvest agricultural products.