Biochemical degradation pathway of dimethoate by Paracoccus sp. Lgjj-3 isolated from treatment wastewater

Dimethoate is a widely used organophosphorus insecticide often detected in the environment. A highly effective dimethoate-degrading Paracoccus sp. strain Lgjj-3 was isolated from treatment wastewater. Strain Lgjj-3 can utilize dimethoate as its sole carbon source for growth and degrade an initial concentration of 100 mg l−1 dimethoate to non-detectable levels within 6 h in liquid culture. During the degradation of dimethoate, seven metabolites, including dimethoate carboxylic acid, 2-(hydroxy(methoxy)phosphorylthio)acetic acid, O,O,S-trimethyl thiophosphorothioate, O-methyl O,S-dihydrogen phosphorothioate, phosphorothioic O,O,S-acid, O,O,S-trimethylphosphorothiate and O,O,O-trimethyl phosphoric ester, were successfully detected and identified based on MS/MS and GC–MS analysis. A biochemical degradation pathway of dimethoate by Paracoccus sp. Lgjj-3 is proposed for the first time. Dimethoate is first hydrolyzed by the scission of the amide bond to form dimethoate carboxylic acid, which is subsequently decarboxylated into O,O,S-trimethyl thiophosphorothioate. The produced O,O,S-trimethyl thiophosphorothioate is oxidized to form O,O,S-trimethylphosphorothiate and then further oxidized to form O,O,O-trimethyl phosphoric ester. O,O,S-trimethylphosphorothiate can also be hydrolyzed at the C–O bond to release a CH3 group and cleavaged at the S–C bond through a hydrolytic pathway to form O-methyl O,S-dihydrogen phosphorothioate. Dimethoate carboxylic acid can also be oxidated at the PS bond to form the corresponding oxon derivative. Next, hydrolysis can occur at the C–O bond to form 2-(hydroxy(methoxy)phosphorylthio)acetic acid, which can be further hydrolyzed at the S–C bond to form O-methyl O,S-dihydrogen phosphorothioate. Phosphorothioic O,O,S-acid is finally formed by the hydrolysis of the C–O bond of O-methyl O,S-dihydrogen phosphorothioate to lose another CH3 group.