Synergistic degradation of organophosphorus insecticide xiaochongthion and its hydrolysate 2,4-dichloro-6-nitrophenol via Cupriavidus nantongensis X1

As highly toxic varieties of organophosphorus insecticides are gradually banned in some countries, medium and low toxicity varieties such as xiaochongthion (XCT) have become substitutes. However, the synergistic toxicity of XCT and its main hydrolysis product 2,4-dichloro-6-nitrophenol (DCNP) for non-target organisms has attracted attention. In this study, we reported a XCT and DCNP degrading strain, Cupriavidus nantongensis X1. Strain X1 could remove 95.29 % of 10 mg/L XCT within 12 h and further degrade DCNP. Two novel metabolites (M187 and M160) were detected and identified via high-resolution mass spectrometry. The structure of two metabolites showed that DCNP could be degraded through a stepwise oxidative dechlorination and denitrification pathway. Meanwhile, the acute and chronic toxicity of metabolites M187 and M160 to aquatic organisms was significantly lower than that of XCT and DCNP. Indicating that the degradation of XCT by strain X1 was a detoxification process. Genomic analysis and enzyme kinetics identified fedA and tcpA were the key genes for strain X1 to degrade XCT and DCNP, respectively. Furthermore, homology modelling and molecular docking were used to determine the catalytic mechanism of TcpA for the dehalogenation and detoxification of DCNP. This study provides a strain resource and a theoretical basis for the efficient and harmless remediation of XCT and its hydrolysis product DCNP residuals.