Bacillus siamensis 3BS12-4 Extracellular Compounds as a Potential Biological Control Agent against Aspergillus flavus

Aspergillus flavus, the primary mold that causes food spoilage, poses significant health and economic problems worldwide. Eliminating A. flavus growth is essential to ensure the safety of agricultural products, and extracellular compounds (ECCs) produced by Bacillus spp. have been demonstrated to inhibit the growth of this pathogen. In this study, we aimed to identify microorganisms efficient at inhibiting A. flavus growth and degrading aflatoxin B₁. We isolated microorganisms from soil samples using a culture medium containing coumarin (CM medium) as the sole carbon source. Of the 498 isolates grown on CM medium, only 132 bacterial strains were capable of inhibiting A. flavus growth. Isolate 3BS12-4, identified as Bacillus siamensis, exhibited the highest antifungal activity with an inhibition ratio of 43.10%, and was therefore selected for further studies. The inhibition of A. flavus by isolate 3BS12-4 was predominantly attributed to ECCs, with a minimum inhibitory concentration and minimum fungicidal concentration of 0.512 g/ml. SEM analysis revealed that the ECCs disrupted the mycelium of A. flavus. The hydrolytic enzyme activity of the ECCs was assessed by protease, β-1,3-glucanase, and chitinase activity. Our results demonstrate a remarkable 96.11% aflatoxin B₁ degradation mediated by ECCs produced by isolate 3BS12-4. Furthermore, treatment with these compounds resulted in a significant 97.93% inhibition of A. flavus growth on peanut seeds. These findings collectively present B. siamensis 3BS12-4 as a promising tool for developing environmentally friendly products to manage aflatoxin-producing fungi and contribute to the enhancement of agricultural product safety and food security.