Investigation of heat-resistant antifungal agents from Bacillus amyloliquefaciens and Bacillus subtilis for biocontrol of mycotoxigenic fungi

Fungal infections of food and feed with toxigenic strains results in the accumulation of harmful metabolites. In this study, the antifungal activity of two indigenous bacterial strains Bacillus amyloliquefaciens and Bacillus subtilis isolated from camel feed was investigated. The potential of the bacterial cell free supernatant (CFS) to reduce mycotoxins synthesis was evaluated, and the impact of their antifungal metabolites on the fungal hyphae was examined. High antagonistic activity was exhibited by both bacterial strains. The best activity was observed against two mycotoxigenic A. niger strains (Sp31 and Sp33) with inhibition zones of 36.75 ± 0.7 mm and 35.75 ±1.5 mm, by strains B. amyloliquefaciens and B. subtilis, respectively. The effects of these bacterial strains' CFSs on mycotoxins synthesis were investigated, and both CFSs were found to reduce the mycotoxins synthesis by A. parasiticus, A. niger and Penicillium spp., in a dose-dependent manner. Moreover, the fungal cell wall morphology was significantly altered by the bacterial CFS at a very low concentration of 1 %. The heat stability of the antifungal metabolites was evaluated at various temperatures ranging from −20 °C to 100 °C, and the metabolites were found to be highly stable, retaining their antifungal activity against A. niger. The antifungal activity of B. amyloliquefaciens and B. subtilis was stable at −20 °C for 236 and 34 days of storage, respectively. These findings suggest that both bacterial strains are exceptional candidates in the biocontrol of mycotoxigenic fungi and in the reduction of their toxic metabolites.