Isolation And Characterization Of Buprofezin-Degrading Strain YL-1:Metabolic Pathway And Application

Buprofezin is a widely used insecticide. Great concerns have been raised about the migration, transformation, degradation of buprofezin in the environment and its potential danger to human body. Therefore, a microorganism capable of degrading buprofezin and study its degradation mechanism have very important theoretical and practical values.A bacterium YL-1capable of degrading buprofezin was isolated from rice plant soil. Based on the morphology, physiological and biochemical characteristics and the homology analysis of its16S rDNA sequence, YL-1was identified preliminarily as Rhodococcus sp.Strain YL-1could grow well from pH5.0-9.0, the optimal pH for its growth was7.0; the optimal temperature was30℃. Glucose and yeast extract were the optimal carbon source and nitrogen source for its growth; ammonium nitrate is the best inorganic nitrogen sources; strain YL-1could also utilize buprofezin as the sole carbon and nitrogen source for growth.Under the conditions of30℃and incubation amount of5%, strain YL-1was able to degrade over90%of buprofezin within48h.30℃and pH7.0was determined as the optimum temperature and pH value for degradation by strain YL-1, respectively. Strain YL-1had a low degradation rate (32.8%) under high concentration of buprofezin (200mg L-1). Based on the analysis of the metabolites appeared during the degradation, we proposed a transformation pathway of buprofezin in Rhodococcus sp. YL-1. The first step of buprofezin degradation in YL-1was to generate catechol and2-tert-butylimino-3-isopropyl-1,3,5-thiadiazinan-4-one, which then subsequently transformed to N-tert-butyl-thioformimidic acid formylaminomethyl ester and2-isothiocyanato-2-methyl-propane followed by conversion to2-isothiocyanato-propane. In our further study, we induced YL-1with different carbon sources, it showed that catechol2.3-dioxygenase activity was strongly induced during the degradation of buprofezin, suggesting that catechol2,3-dioxygenase is a critical enzyme in the multistep biodegradation of buprofezin by Rhodococcus sp. YL-1. The results indicating that buprofezin might be converted into catechol.The bioremediation of buprofezin contaminated soil by inoculating YL-1was studied under laboratory conditions. After addition of108cells g-1dry soil into soil,85.3%of buprofezin at concentration of10mg kg-1dry soil was degraded at25d, whereas only12.1%of buprofezin was degraded in uninoculated soil; after25d, strain YL-1that added to the soil was still able to detected (1.9×107cfu g-1), indicating exogenous degrading bacterium YL-1could significantly improve the degradation rate of buprofezin in soil, and strain YL-1could also sustain itself in the natural environment for a long period. The degradation rate was related positively to the amount of inoculation. When the initial concentration of buprofezin was50mg kg-1in the soil, the degradation rate was only40.6%. The optimal temperature for buprofezin degradation by YL-1in soil was30℃. Adding glucose and organic fertilizer materials to the soil could increase the degradation rate of buprofezin by strain YL-1.