Enhancing biological control of apple rot: Unveiling the antifungal potential and mechanism of Bacillus amyloliquefaciens HZ-12′s lipopeptide

Abstract

Rot caused by fungal pathogen Aspergillus niger is an important postharvest disease of apples. To control the apple rot resulting from A. niger, five Bacillus strains with antagonism against A. niger were screened by Oxford cup diffusion method. Among them, Bacillus amyloliquefaciens HZ-12 had the most prominent antifungal activity, and its control effect reached 89.0 % on apple rot caused by A. niger. Moreover, the antifungal substances from B. amyloliquefaciens HZ-12 were analyzed, and the lipopeptide was suggested to be the key substance due to strong antifungal stability and surface activity. The lipopeptide extract was confirmed to damage the cell wall and membrane of A. niger, leading to leakage of intracellular nucleic acids and cell death. Further genetic engineering by insertion of a strong promoter significantly improved the iturin A yield by 4.2-fold, and corresponding antifungal effect of B. amyloliquefaciens was obviously increased. This study provided a new strain for biological control of apple rot disease, and also indicated the lipopeptide as antifungal and its corresponding antifungal mechanism.