The lipopeptide antibiotic fengycin, produced by Bacillus subtilis, strongly inhibits growth of filamentous fungi. In this study, we evaluated the effects of fengycin treatment on apoptosis and necrosis in Rhizopus stolonifer by means of cell staining and epifluorescence microscopy. At fengycin concentrations less than 50 μg/ml, treated fungal cells demonstrated a dose-dependent increase in apoptosis-associated markers compared with the untreated control. These markers included chromatin condensation, reactive oxygen species accumulation, mitochondrial membrane potential depolarization, phosphatidylserine externalization, and the occurrence of DNA strand breaks. These results showed that fungal cells were impaired in a number of important functions and entered apoptosis upon treatment with low concentrations of fengycin. In contrast, high concentrations (>50 μg/ml) induced necrosis, indicating that the fungicidal action of fengycin operates via two modes: apoptosis at low concentrations and necrosis at high concentrations. Additionally, the apoptotic effect that we have shown suggests that lower concentrations of fengycin than previously thought may be effective for food preservation.

Bacillus subtilis strain PB2-L1 produces the lipopeptide surfactin, a highly potent biosurfactant synthesized by a large multimodular nonribosomal peptide synthetase (NRPS). In the present study, the modules SrfA-A-Leu, SrfA-B-Asp, and SrfA-B-Leu from surfactin NRPS in B. subtilis BP2-L1 were successfully knocked-out using a temperature-sensitive plasmid, pKS2-mediated-based, homologous, recombination method. Three novel surfactin products were produced, individually lacking amino acid Leu-3, Asp-5, or Leu-6. These surfactins were detected, isolated, and characterized by HPLC and LC-FTICR-MS/MS. In comparison with native surfactin, [∆Leu3]surfactin and [∆Leu6]surfactin showed evidence of reduced toxicity, while [∆Asp5]surfactin showed stronger inhibition than native surfactin against B. pumilus and Micrococcus luteus. These results showed that the minimum inhibitory concentration of [∆Leu6]surfactin for Fusarium moniliforme was 50 μg/mL, such that [∆Leu6]surfactin could lead to mycelium projection, cell damage, and leakage of nucleic acids and protein. These factors all contributed to stimulating apoptosis in F. moniliforme. The present results revealed that [∆Leu6]surfactin showed a significant antifungal activity against F. moniliforme and might successfully be employed to control fungal food contamination and improve food safety.