Unravelling OTA-detoxification by the dioxin-mineralizing bacterium Rhizorhabdus wittichii RW1T

Abstract

Environmental pollution remains a critical concern for public health, necessitating innovative remediation strategies. In this regard, microorganisms play a pivotal role by naturally degrading and eliminating various pollutants. The Rhizorhabdus wittichii RW1^T strain is recognized for its ability to metabolize a broad spectrum of toxic and persistent environmental contaminants. Given the relevance of ochratoxin A (OTA) as a harmful mycotoxin affecting agricultural settings, this study investigates the capability of R. wittichii RW1^T (DSM 6014^T) in neutralizing OTA. Experimental results demonstrate that this strain effectively breaks down OTA by hydrolyzing its amide bond, leading to the production of ochratoxin α and L-β-phenylalanine, both of which are non-toxic. Computational genome analysis of R. wittichii RW1^T revealed genes encoding proteins homologous to known OTA-degrading amidohydrolases. This investigation identified a 438-amino acid protein (ABQ67280.1), whose recombinant form (RwOTA) efficiently hydrolyzes OTA and ochratoxin B through a catalytic mechanism involving a binuclear metal center. This center facilitates the polarization of the carbonyl group of the scissile amide bond of OTA and activates a water molecule for hydrolysis. Screening against a synthetic peptidase substrate library indicated a highly specific hydrolytic activity for RwOTA. Structural modeling and molecular docking simulations provided insights into the interaction of ochratoxins with RwOTA, shedding light on its substrate specificity. The gene encoding RwOTA presents a promising addition to the extensive repertoire of biodegradation-associated genes within R. wittichii RW1^T, reinforcing its potential in environmental pollutant detoxification.