Isolation of a diazinon-degrading strain Sphingobium sp. DI-6 and its novel biodegradation pathway

Diazinon is one of the most widely used organophosphate insecticides, one that is frequently detected in the environment. In this study, a diazinon-degrading bacterium, DI-6, previously isolated from diazinon-contaminated soil in China has been subsequently identified as Sphingobium sp. on the basis of its physiological and biochemical characteristics, as well as by virtue of a comparative analysis of 16S rRNA gene sequences. This strain is capable of using diazinon as its sole carbon source for growth and was able to degrade 91.8% of 100 mg L^-1 diazinon over a 60-h interval. During the degradation of diazinon, the following seven metabolites were captured and identified by gas chromatography/mass spectrometry (GC-MS) analysis: diazoxon, diazinon aldehyde, isopropenyl derivative of diazinon, hydroxyethyl derivative of diazinon, diazinon methyl ketone, O-[2-(1-hydroxyethyl)-6-methylpyrimidin-4-yl] O-methyl O-hydrogen phosphorothioate, and O-(6-methyl pyrimidin-4-yl) O,O-dihydrogen phosphorothioate. Based on these metabolites, a novel microbial biodegradation pathway of diazinon by Sphingobium sp. DI-6 is proposed. This research provides potentially useful information for the application of the DI-6 strain in bioremediation of diazinon-contaminated environments.