Enzymatic degradation of mycotoxin patulin by a short-chain dehydrogenase/reductase from Bacillus subtilis and its application in apple juice

Patulin (PAT), a notorious mycotoxin widely found in fruits and their derived products, poses serious health risks to humans and animals due to its high toxicity. Biodegradation based on microbial enzymes has shown broad application prospects in controlling PAT contamination due to its environmental friendliness, high efficiency, strong specificity, and mild conditions of action. Bacillus subtilis is a cosmopolitan probiotic bacterium with an extensive enzymatic profile, which could serve as a valuable resource for the effective production of a range of enzymes utilized in various industrial processes and production applications. In this work, we demonstrated that a short-chain dehydrogenase/reductase from B. subtilis (BsSDR) that can effectively convert PAT to the non-toxic E-ascladiol. Multiple sequence alignment results revealed that BsSDR displayed less than 30% identity with the previously reported PAT-degrading enzymes, indicating that it is a novel PAT-degrading enzyme. BsSDR exhibited a powerful PAT-degrading ability and strong PAT tolerance, as it was capable of degrading over 95% of PAT at initial concentrations of 50–500 μM. In addition, BsSDR exhibited the highest activity at pH 8.0 and 40 °C, and retained more than 60% residual activity after incubation at 40 °C for 3 h, indicating a remarkable thermostability of BsSDR. Molecular docking and site-directed mutagenesis indicated that the catalytic triad formed by the residues (S, Y, and K) was the key for short-chain dehydrogenase/reductase activity and this conserved catalytic mechanism was followed in BsSDR catalysis. More importantly, BsSDR is able to eliminate 83.61% of PAT in apple juice without compromising its quality during the biodegradation process. These results suggest that BsSDR may serve as a promising detoxification agent for the degradation of PAT in food processing.