Analysis of the subtype I amidohydrolase responsible for Ochratoxin A degradation in the Sphingomonas genus

Ochratoxin A (OTA) is a mycotoxin that contaminates the agricultural environment, food and feed, leading to substantial economic losses. Among the alpha-proteobacteria, certain strains from the Sphingomonas genus are known to degrade a wide range of naturally occurring and synthetic compounds, including OTA. In this work, type strains for 17 Sphingomonas species were tested for their ability to detoxify OTA in culture. Most of them demonstrated OTA-detoxification capabilities. We observed that all OTA-degrading strains possessed an amidohydrolase homologous to others identified in gamma-proteobacteria. Conversely, strains that did not degrade OTA lacked this enzyme. This strong correlation suggests that the OTA-degrading phenotype exhibited by Sphingomonas cultures is directly linked to the presence of this enzyme. A PCR-based detection method was designed to identify strains possessing the amidohydrolase-encoding gene, marking them as potential OTA-degrading strains. Additionally, the OTA-transforming amidohydrolase from S. dokdonensis DSM 21029^T (SdOTA) was identified and biochemically characterized. In silico prediction of the SdOTA structure with AlphaFold, combined with molecular docking simulations, revealed the structural basis of the substrate specificity and insights into the mycotoxin-binding mechanism. The ability Sphingomonas strains to detoxify OTA, coupled with the collection of genes enabling bioremediation, positions them as highly versatile bacteria for pollutant detoxification.