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

Jian Jiang, Ling Gao, Xiaomei Bie, Zhaoxin Lu, Hongxia Liu, Chong Zhang, Fengxia Lu, Haizhen Zhao

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, [∆Leu(3)]surfactin and [∆Leu(6)]surfactin showed evidence of reduced toxicity, while [∆Asp(5)]surfactin showed stronger inhibition than native surfactin against B. pumilus and Micrococcus luteus. These results showed that the minimum inhibitory concentration of [∆Leu(6)]surfactin for Fusarium moniliforme was 50 μg/mL, such that [∆Leu(6)]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 [∆Leu(6)]surfactin showed a significant antifungal activity against F. moniliforme and might successfully be employed to control fungal food contamination and improve food safety.