Optimizing conditions for the production of antifungal agents using the native Bacillus cereus SB15

With regard to the occurrence of fungal infections, finding new antifungal agents is necessary. Due to its biologic properties Bacillus spp. are suitable sources for this purpose. The aim of this study was to find native bacillus species with potential of antifungal agent production.
Material and In this experimental study, bacillus species were isolated from heat-treated soil samples and following culturing in TSB, anti-fungal effects of their supernatants were determined by disc diffusion method. Minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) levels of the selected strains were obtained against two fungal pathogens. Growth curve of the isolate was obtained in different pH and temperatures. The effects of pH, temperature, carbon and nitrogen sources on antibiotic production by the isolate were also investigated. This isolate was identified through biochemical and molecular tests.
Three out of six bacillus isolates were able to produce the antifungal agents, among them Bacillus cereus strain SB15 showed the most significant antifungal effects against a wide range of fungi. Optimized conditions for antibiotic production by this isolate were: temperature=37˚C, pH=7, 48 h incubation and manitol and urea as the best carbon and nitrogen sources, respectively. The MIC and MFC of the produced antibiotic against Aspergillus niger were: 2 and 4 and against Aspergillus flavus 4 and 16 mg/ml, respectively.
Based on the obtained results it may be concluded that this bacillus strain has optimum potential for antifungal agent production. The strain can be used for the control of fungal infections and also fungal growth in food industry and environment.