Cell-Free Supernatant of Bacillus subtilis Suppresses the Mycelial Growth of Penicillium expansum by Destroying the Cell Membrane Integrity and Provoking Cell Death

<i>Penicillium expansum</i> inflicts significant economic damage in the fruit and vegetable industry due to its wide distribution and ability to infect a diverse range of hosts. Therefore, developing safe and environmentally sustainable strategies to suppress the growth of this pathogen is of critical importance. <i>Bacillus subtilis</i>, recognized for its broad antimicrobial activity and widespread occurrence, has been widely utilized in the biological management of plant diseases. This research seeks to assess the inhibitory potential of <i>B. subtilis</i> against <i>P. expansum</i>. The cell-free supernatant (CFS) derived from <i>B. subtilis</i> significantly suppresses the germination of spores, germ tube extension, and hyphal development of <i>P. expansum</i>. It also reduces disease incidence in grapes and citrus and suppresses the expansion of lesions. Further investigation had shown that it induced mycelium reactive oxygen species (ROS) accumulation, destroyed the cell membrane integrity, led to leakage of cytoplasmic contents and induced membrane lipid peroxidation. Moreover, exposure to high concentrations of CFS results in mycelial contraction and morphological abnormalities, triggering the disintegration of intracellular organelles and markedly upregulating the expression of apoptosis-like programmed cell death genes. The self-protective response elicited by 5% CFS is insufficient to counteract the extent of cellular damage, ultimately driving cells toward a dynamic, multistage, and disintegrative form of cell death. The findings of this study offer a theoretical foundation for managing <i>P. expansum</i> after harvest.