Screening Of Cypermethrin Degrading Bacterium And Studies On Its Characteristics

A cypermethrin degrading strain TR2 was isolated from tea-plant. It was identified to be Bacillus cereus and proved to be able to colonize inside of tea-plant. The optimal conditions for the aerobic degradation of cypermethrin by the strain should be Nutrition Agar substrate with the content of 25mg/L cypermethrin, at 36°C, with pH 7.8 and 96 hours after inoculation. 3-phenoxy benaldehyde and benzoic acid were proved to be the metabolites of cypermethrin. Strain TR2 was found to degrade befenthrin and fenpropathrin efficiently, and also to be able to degrade methamidophos, dichlorvos and chlorpyrifos. The extracellular crude enzyme of the strain was proved to have no degradation to cypermethrin, while the intracellular one had high degradation to cypermethrin. The suitable pHs and temperatures for the crude enzyme were 5.5-9.0 and 30-45°C respectively, and the optimal pH and temperature were 8.0 and 35°C respectively. The crude enzyme was also proved to be stable at pH6.0-9.0 and below 40°C. The Michaelis-constant (K_m) and maximum velocity (V_max) were 692.39nmol/mL and 89.29nmol/min respectively. The optimal conditions for the degradation of cypermethrin in the pot experiment were that spraying cypermethrin should be one day after spraying bacteria, each tea-plant was sprayed with 1mg/kg cypermethrin and 5 mL culture liquid and kept for 10 days. The degrading rate of cypermethrin by strain TR2 was tested to be 83.4% in the plot experiment of tea-garden, and the cypermethrin residue was below 0.15mg/kg.