Three newly identified peptides from Bacillus megaterium strongly inhibit the growth and aflatoxin B1 production of Aspergillus flavus

Aspergillus flavus is one of the major moulds that infect crops, and produces the most carcinogenic and toxic compounds-aflatoxins. The previous research demonstrated that a marine bacterium, Bacillus megaterium, inhibited the growth of A. flavus and the biosynthesis of aflatoxin B1 in peanuts. In this study, five characterized peptides with distinct structures in three ion peaks were identified by LC-MS/MS and demonstrated to have anti-A. flavus activities from B. megaterium fermentation broth. Based on the structural information generated from the peptides, several derivatives (different composition and configuration) were synthesized and examined their efficacy in terms of inhibiting growth of A. flavus, spore germination, and aflatoxin production. Results showed three peptides L-Asp-L-Orn (D1O), L-Asp-L-Asn (D1N) and L-Asp-L-Asp-L-Asn (D2N) could significantly inhibit the growth of A. flavus. The results of confocal microscopy showed that D1O, D1N and D2N can spontaneously enter into the hyphae of A. flavus. Meanwhile, data of quantitative RT-PCR (qRT-PCR), aflatoxin production and spore germination assay demonstrated that after three peptides entered into the cells of A. flavus, they inhibited conidiation and aflatoxin production, but didn't inhibit hyphae vegetative growth and spore germination.