Bacillus velezensis A4 Against Fungal Pathogens via Membrane Integrity Disruption and Cellular Dysfunction in Fungal Pathogens

Fruit decay caused by pathogenic fungi result in serious economic and quality losses during the postharvest stage. Biological control has evolved as a promising solution to these issues due to its environmentally friendly and safe characteristics. This study investigated the inhibitory effect of the biological control agent <i>Bacillus velezensis</i> A4 on various fungi and elucidated its antifungal mechanism. The strain demonstrated an antagonistic effect against 12 pathogenic fungi to different degrees, as well as the primary antifungal substances present in the cell-free supernatant (CFS). CFS induces the deformation of pathogenic hyphae and disrupts the permeability of hyphal cell membranes for effective biological control. Transcriptome and metabolome analysis showed that CFS disrupted lipid homeostasis and intracellular organization. In addition, the application of CFS leads to upregulation of membrane oxidation-related genes and the caspase gene family, thereby initiating the process of apoptosis. Our findings suggest that the broad-spectrum antifungal activity exhibited by <i>B. velezensis</i> A4 in CFS is due to the disruption of fungal cell membrane integrity and induction of fungal cell apoptosis-related pathways.