Study On The Characteristics Of Beta-Cypermethrin Degrading Bacteriaand Degrading Enzyme

Great concerns have been raised on the residues and degradation of pyrethroid insecticide in the environment. Biodegradation is an effective way to eliminate the pyrethroid residues in soil, sediment and agricultural products. Therefore, in this study, pyrethroid degrading bacteria were isolated from the environment, and the degrading enzymes were partially purified and characterizied. The results are as follows:9 soil samples were collected from the environment treated with SPs. More than 110 strains were screened by two kinds of screening procedures: the enrichment screening method and the multi-plate screening method, in both methods theβ-cypermethrin is as a carbon source (100 mg / L). As the results, 18β-cypermethrin-degrading bacteria were obtained. Theβ-cypermethrin degradation rate of these strains were analyzed by High Performance Liquid Chromatography. Theβ-cypermethrin degradation rates of seven strains were above 50%. The strain E1 has the highest degradation rate of 80.07%. The strains C1, E1 and I3 have higher rate of degradation, the preliminary identification of these three strains were carried out by morphological, physiological and biochemical tests, and the optimization of culture conditions were also studied.Strain CY22-7 was isolated by our labolatory and have been identified as Sinorhizobium sp.. It is the first report that Sinorhizobium sp. strain can degradeβ-cypermethrin, therfore this strain was selected for further study. The time of strain CY22-7 cultured in LB medium and in the cypermethrin medium to achieve stability was 36 h, 72 h, respectively. In order to verify the stability of degrading ability of strain CY22-7, the subculture of 1st generation, 5th generation, 10 generations, showed a similar growth curve cultured in LB medium, and also in enriched medium; after cultured in cypermethrin(100 mg / L) medium for 5 d the cypermethrin pesticide degradation rates were close, indicating that the cypermethrin degrading bacteria CY22-7 has good ability of degradation and stability.The domain of the cypermethrin degrading enzyme from bacteria CY22-7 were determined. Extracellular enzymes were extracted by ammonium sulfate precipitation, and intracellular enzyme were extracted by cell disruption and centrifugation. Measured by the degradation that extracellular enzyme activity was higher in the degradation of cypermethrin while intracellular enzyme activity is lower. Shown that the cypermethrin degrading enzyme is extracellular.According to the total protein intracellular and extracellular produced by degradation cypermethrin bacteria CY22-7 in the cypermethrin medium within 1⁶ d, the fourth day is determined as the best enzyme production time.The optimum pH is 7.0; enzyme activity has better stability in pH6 8; the optimum temperature is 42℃; enzyme activity has better stability when the temperature is below 30℃. Different metal ions have different effects on the activity of cypermethrin degrading enzymes. Mg²⁺ has little effect on the enzyme ability to degrade cypermethrin. Mn²⁺ and Cu²⁺ have a certain extent effect on the enzyme degradation of cypermethrin. And Zn²⁺, Fe²⁺ can strongly inhibit the enzyme on the degradation of cypermethrin.