Modeling the effect of environmental factors on growth and toxin production of Aspergillus versicolor in wheat and the potential biocontrol effect of Bacillus subtilis HJ4

Sterigmatocystin (STC), a mycotoxin that pollutes wheat and other grains and is related to health risks, has attracted increasing attention. In this study, we have explored the toxicity conditions of Aspergillus versicolor in wheat and identified a potential biological control method. By constructing a water activity (Aw)-water content curve, the effects of temperature, Aw, and culture time on toxin production by A . versicolor in wheat were determined. The Aw was found to be 0.96, and the concentration of STC in wheat reached the maximum (105.7 mg/kg) after 10 d of culture at 28 degrees C. Biocontrol bacteria were screened using plate confrontation, agar diffusion, and co-culture in wheat. The results showed that Bacillus subtilis HJ4 has significant antifungal activity against A. versicolor in vitro and in vivo. In vivo experiments showed that B. subtilis HJ4 significantly reduced the toxicity of A. versicolor to wheat (51%) on day-7, but the control effect was weakened (10%) on day-20. Finally, research on the antifungal mechanism of B. subtilis HJ4 revealed that its action primarily relies on competition for space and nutrients, destroying the cellular structure of the fungus and secreting substances with antifungal activity, such as proteins, cyclic lipopeptides, and oligosaccharides, aiding in control against A. versicolor. In summary, this study has emphasized the influence of environmental factors on the growth and toxin production of A. versicolor in wheat and evaluated the potential of B. subtilis HJ4 in reducing the pollution caused by A. versicolor and STC in wheat.