Identification of novel surfactin derivatives from NRPS modification of Bacillus subtilis and its antifungal activity against Fusarium moniliforme

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.