Fengycins, Cyclic Lipopeptides from Marine Bacillus subtilis Strains, Kill the Plant-Pathogenic Fungus Magnaporthe grisea by Inducing Reactive Oxygen Species Production and Chromatin Condensation

Rice blast caused by the phytopathogen Magnaporthe grisea poses a serious threat to global food security and is difficult to control. Bacillus species have been extensively explored for the biological control of many fungal diseases. In the present study, the marine bacterium Bacillus subtilis BS155 showed a strong antifungal activity against M. grisea. The active metabolites were isolated and identified as cyclic lipopeptides (CLPs) of the fengycin family, named fengycin BS155, by the combination of high-performance liquid chromatography (HPLC) and electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS). Analyses using scanning and transmission electron microscopy revealed that fengycin BS155 caused morphological changes in the plasma membrane and cell wall of M. grisea hyphae. Using comparative proteomic and biochemical assays, fengycin BS155 was demonstrated to reduce the mitochondrial membrane potential (MMP), induce bursts of reactive oxygen species (ROS), and downregulate the expression level of ROS-scavenging enzymes. Simultaneously, fengycin BS155 caused chromatin condensation in fungal hyphal cells, which led to the upregulation of DNA repair-related protein expression and the cleavage of poly(ADP-ribose) polymerase (PARP). Altogether, our results indicate that fengycin BS155 acts by inducing membrane damage and dysfunction of organelles, disrupting MMP, oxidative stress, and chromatin condensation, resulting in M. grisea hyphal cell death. Therefore, fengycin BS155 and its parent bacterium are very promising candidates for the biological control of M. grisea and the associated rice blast and should be further investigated as such. IMPORTANCE Rice (Oryza sativa L.) is the most important crop and a primary food source for more than half of the world's population. Notably, scientists in China have developed several types of rice that can be grown in seawater, avoiding the use of precious freshwater resources and potentially creating enough food for 200 million people. The plant-affecting fungus Magnaporthe grisea is the causal agent of rice blast disease, and biological rather than chemical control of this threatening disease is highly desirable. In this work, we discovered fengycin BS155, a cyclic lipopeptide material produced by the marine bacterium Bacillus subtilis BS155, which showed strong activity against M. grisea. Our results elucidate the mechanism of fengycin BS155-mediated M. grisea growth inhibition and highlight the potential of B. subtilis BS155 as a biocontrol agent against M. grisea in rice cultivation under both fresh- and saltwater conditions.