Low-dose gamma irradiation enhances the enzymatic ochratoxin A detoxification potential of a soil-derived Bacillus thuringiensis

Contamination of food by Aspergillus niger is a serious global food safety issue due to ochratoxin A (OTA). This study evaluates the use of low-dose gamma irradiation to maximize the mycotoxin-detoxifying properties of a native Bacillus thuringiensis biocontrol agent isolated from soil. A soil-derived B. thuringiensis strain demonstrated significant intrinsic antifungal activity against an OTA-producing A. niger isolate, which was correlated with the production of chitinases, glucanases, and proteases. To maximize this biocontrol potential, gamma irradiation of bacterial cell-free filtrates was performed. A 0.2 kGy dose of radiation optimally increased the bioactivity of the filtrate, increasing the inhibition of A. niger radial growth (from 82.8 to 88.3% compared to the untreated control) and the enzymatic breakdown of OTA into the less toxic ochratoxin α (OTα) in both liquid cultures and contaminated wheat grains. Enzymatic activity tests showed that the 0.2 kGy irradiation exposure produced an 18.06% increase in carboxypeptidase activity. Moreover, FTIR analysis and in silico molecular docking were used to provide supportive mechanistic information about the increased activity observed following irradiation. The findings indicate that the structural alterations caused by mild radiation stimulated enzyme-substrate interactions and increased the binding affinity of the carboxypeptidase enzyme to OTA, without destroying its structural scaffold. These results indicate that low-dose gamma irradiation can be an extremely useful method for enzymatic activity improvement, which can be considered a promising and feasible biotechnological solution for mycotoxin mitigation in agricultural matrices.