Bacillus Subtilis B-FS06 Inhibition Of Aspergillus Flavus And Investigation Of Its Antifungal Compounds

Aspergillus flavus is a plant and human pathogen. It can invade crops (such as peanuts and maize) and produce aflatoxins during corn storage. Aflatoxins can cause acute hepatitis, immunosuppression and hepatocellular carcinoma. It's one of the main reasons to induce to live cancer. China is one of the major countries of peanut production, consumption, and export. Toxic effect of A. flavus contamination is disastrous for Chinese peanut industry.At present, internal studies on A. flavus are focusing on improving aflatoxins determine method. There are few reports about control of A. flavus. While external studies on A. flavus are focusing on biological control, which include directly using antagonistic microbes and extracting antifungal compounds from plants and microorganisms to inhibit A. flavus growth and spore germination. Although many antifungal compounds have been found against A. flavus up to now, few of them could be used in practice.As A. flavus contamination causes tremendous economic loss, it is urgent to find a valid method to control A. flavus contamination. Many studies focus on biological control of A. flavus recently. Our group devotes to using microbes to inhibit A. flavus and we have isolated several antagonistic microbes. The strain B-FS06 was investigated in this study as having the highest antifungal activity. The results were described as below:(1) Strain B-FS06 was identified as B. subtilis by its morphological characters and its 16S rDNA sequence. (2) Antifungal test results showed that the cell-free culture filtrate (CCF) of B-FS06 could inhibit many phytopathogens, and significantly inhibit the growth and spore germination of A. flavus. Its antifungal activity was insusceptible after treatment under different temperature and pH. The active compounds could be precipitated by ammonium sulfate, and were insusceptible to proteinase K, pepsin and PMSF. Microtitre plate assay showed the (MIC) against A. flavus is 31.2μg/mL and disc plate diffusion assay showed the MIC is 12.5μg/well. (3) After purification, two lipopeptides surfactin and bacillomycin D were determined by MS. Comparing those previous studies, we consider that bacillomycin D acted the anti-A. flavus activity. It was noted that the growth of A. flavus could be inhibited completely at the compounds concentration of 200μg/g on peanuts.Antifungal compound bacillomycin D was found in strain B-FS06 culture in this study. This is the first report to study bacillomycin D inhibiting the spore germination in vitro and the growth of A. flavus on peanuts. A. flavus is widely occurred during food storage. Our research suggested that bacillomycin D would be an ideal candidate to control peanut contamination by A. flavus during food storage.