Surfactin Variants from Bacillus subtilis natto CSUF5 and Their Antifungal Properities Against Aspergillus niger

An antifungal Bacillus strain isolated from the traditional fermented food natto was identified and named as B. subtilis natto CSUF5. Antifungal metabolites of the strain were extracted from the medium of the inhibition zone on the dual culture plate. 2 V-7-surfactin isoforms (C-14-V-7, C-13-E-1(met) -V-7) and 3 I/L-7-surfactin isoforms (C-13-I/L-7, C-13,(14)-E-1(met)-I/L-7) were identified from the RP-HPLC isolations by MSn (n = 1,2,3) analysis. Both V-7-surfactins and I/L-7-surfactins showed slight antifungal activity against A. niger, and their MIC50 decreases in the order V-7 > I/L-7. EDTA was found to be an effective strengthening agent which could cooperate with the surfactin variants and enhance their antifungal activity greatly. Microscopic observations revealed that the surfactin variants could delay the fungal spore germination and inhibit the hyphae growth, mainly displayed in hyphal shriveling and distortion. Surfactin variants and EDTA together could lead the hyphae to severe helical warping and fracture. These results will provide promising references for the development of new antifungal products.