Biotransformation of thianicotinyl neonicotinoid insecticides: Diverse molecular substituents response to metabolism by bacterium Stenotrophomonas maltophilia CGMCC 1.1788

The carbon atom that neighbors the tertiary amine attached to the 6-chloro-3-pyridinylmethyl moiety is the key active site in the hydroxylation of the neonicotinoids imidacloprid and thiacloprid as well as in the demethylation of acetamiprid by Stenotrophomonas maltophilia CGMCC 1.1788. In this study, thianicotinyl neonicotinoid insecticides having diverse molecular substituents were biotransformed by S. maltophilia CGMCC 1.1788. The results indicated that the substitution of 6-chloropyridyl in imidacloprid with 2-chlorothiazol in imidaclothiz did not affect the hydroxylation of imidaclothiz and its hydroxylated site, while the oxadiazinane ring in thiamethoxam was not hydroxylated or opened. Moreover, the N-methyl group in clothianidin and thiamethoxam was not demethylated by S. maltophilia CGMCC 1.1788. The biotransformation of imidaclothiz was inhibited by piperonyl butoxide, implying that both hydroxylation and dehydrogenation are mediated by a P450 monooxygenase. The bioassay results suggested that the activity of 5-hydroxy and olefin imidaclothiz was similar but less than that of imidaclothiz against the horsebean aphid Aphis craccivora and mosquito larva Culex pipiens, while 5-hydroxy IMT showed weak activity against the brown planthopper Nilaparvata lugens.