Enhanced biocontrol of postharvest blue mold in apple by phytopathogen targeted Bacillus subtilis 507

Postharvest blue mold in apples caused by Penicillium expansum poses a great risk to food safety. Here, we report on a phytopathogen targeted enrichment strategy that led to the isolation of an endophytic biocontrol agent (BCA), Bacillus subtilis 507, with strong antagonism against P. expansum. Using a unique dual application approach that combines both live BCA and its crude metabolites (Bac + CM), our result showed an enhanced efficacy. Relative to the control, the disease incidence of blue mold in apples was reduced by 45.95% and lesion diameter was limited to 19.18 mm. Untargeted metabolomics identified bioactive compounds, including 3-phenyllactic acid, pipecolic acid, and spermine, suggesting direct antifungal activity and host based modulation. The mechanistic investigations showed that Bac + CM inhibited spore germination up to 37.3%, and depletion of ergosterol with 97.09% cellular membrane leakage. Fungal hyphal deformation and structural collapse were confirmed by SEM. The BCA rapidly colonized apple fruit wounds and surfaces up to 9.4 log10CFU and reduced natural decay to 5.13% without affecting fruit quality. This study presents a combined, metabolite-enhanced biocontrol strategy that positions B. subtilis 507 as a promising candidate for sustainable management of postharvest food diseases such as blue mold in apples.