Microbial Metabolism Of Neonicotinoid Insecticide Thiamethoxam And Thiamethoxam Oxazine Research

This study conducted the isolation and identification of microorganisms with the ability of degradation of neonicotinoid insecticides thiacloprid (THI) and thiamethoxam (TMX) from the rapid degradating THI and TMX soil, then the degrading conditions and metabolic pathways have been further studied. The bacterial diversity in the mineral salt broth inoculated with soil extract which was capable of degradation of TMX has been also examined.1. Two bacteriums were isolated from the soil which exhibited high THI biodegradability:strain THI-A and strain THI-B. The isolates were identified by BLAST analysis of16S rDNA sequences, the THI-A isolate were identified as a species of genus Ochrobactrum; the THI-B isolate identified as a species of genus Acinetobacter.The accession numbers in Genebank were JF414756、 JN098518,respectively. Ochrobactrum sp. THI-A and Acinetobacter sp. THI-B can transform THI in cyanoimine group with hydrolysis to form amide metabolite. Both the growing cells and resting cells of Ochrobactrum sp.THI-A and Acinetobacter sp. THI-B can degradate THI, but the transforming activities are very low. The impact of soil extract on the Ochrobactrum sp.THI-A and Acinetobacter sp.THI-B transforming THI activity was studied.The results showed that the soil extract can not promote the growing cells of Ochrobactrum sp.THI-A and Acinetobacter sp.THI-B transforming activity,but it did to resting cells,and the transforming activities were increased by2.5times and1.5times, respectively. But the overall conversion efficiency was still low, the degradation ratio was13.8%、.6.6%, respectively.2. In the mineral salts medium, the soil from Hainan could rapidly degradate TMX which was the sole carbon and nitrogen sources, and31bacteriums were isolated from plate.But only11had the degradation activity, strain TMX-23had the highest degradation of the TMX. Strain TMX-23was identified as a species of genus Ensifer adhaerens. Accession numbers in Genebank was JN098520.E. adhaerens TMX-23could transform TMX in Nitro-amino group with deoxidization to form Nitroso and Carbonyl metabolites by LC-MS analysis. The resting cells of E.adhaer-ens TMX-23could not degrade TMX in Phosphate buffer solution, but the growing cells did in mineral salts medium, the degradation ratio was38.6%, with half-lives of8.2d.1%Glucose could significantly promote the increase of E.adhaerens TMX-23biomass (seven times than not plus glucose group), but did not promote the degradation of TMX, the degradation ratio was only15%in15days. This metabolism was different from the microorganisms reported in the literature, Leifsonia sp.PC-21, Pseudomonas sp.Gl, R.mucilaginosa IM-2and Stenorophomonas maltophilia CGMCC1.1788, with the cometabolic mechanism in neonicotinoid insecticides. E.adhaerens TMX-23had the capacity of biological nitrogen fixation. The concentration of l’Omg/L TMX could significantly promote the increase of E.adhaerens TMX-23biomass, biomass increased by1.3times to the control group.The diversity of the bacterial consortia degrading TMX was studied by16S rDNA PCR-DGGE method.Nine bands were sliced from the gel, amplified by PCR and sequenced. The blast analysis results showed that band5and band6belonged to Achromobacter sp. and E. adhaerens, respectively.And the rest7bands were all uncultured bacterium. Thus, we concluded that the uncultured bacterium in the mixed bacteria played an important role in the rapid degradation of TMX.