Screening And Degrading Characterization Of Dominant Bacteria For The Degradation Of Cypermethrin

Pesticides are used to control plant diseases, insect pests, weeds and regulate plant growth, and play an important role in agricultural production. However, due to large number of long-term and extensive application, pesticides cause pesticide residues in the soil environment and endanger plants, animals and human's health. While it is generally considered that pyrethroid pesticides have the characteristics of high efficiency and low toxicity, but they also have optical and thermal stability characteristics, therefore, they have long half-life period in environment, and very difficult to degrade rapidly under natural conditions. Cypermethrin is more hydrophobic and more difficult to be degraded in pyrethroid pesticides. Because of the physical and chemical degradation of pesticides of the traditional method will still bring secondary pollution, in recent years, as a low-cost and environmental-friendly technology of contaminated soil, bioremediation has become a hot research and use microbial degrade pesticides has also become the development trend of harmless technology.In this study six cypermethrin degrading-bacteria were isolated from the soil prayed with cypermethrin, and one of them named L0, which could degrade cypermethrin stably and had the highest rate of degradation. By studying its morphology and physiological-biochemical characteristics, the strain L0 was initial identified belong to Bacillus bacteria (Bacillus sp.).Further study of L0 strain of the best growth conditions were as follows:in the general medium, L0 could reach the maximum amount of growth after 72 hours, but in the inorganic salt medium, it only used 48 hours; the optimum growth temperature was 26℃, the best initial pH was 7, the best source of nitrogen was peptone and the best carbon source was glucose; when the glucose concentration was 1%, the optimum C:N was 20:1; best inorganic ion concentrations:Na+ 0.2g/L, K+ 0.6g/L and Mg2+ 0.5g/L. This study used gas chromatography to analysis the degradation of cypermethrin of Lo. Grew in the best conditions, the degradation rate of cypermethrin of Lo could reach 87.5%. The best conditions of cypermethrin degradation of Lo were as follow:temperature 26℃, pH 7, substrate concentration 100 mg/L; added a small amount of additional carbon source (glucose) could promote Lo to degrade cypermethrin, the best plus carbon concentration was 200 mg /L.Preliminary studied the effect of microbial remediation to the cypermethrin contaminated soil by Lo. After it was augmentative cultured, added the strain to the simulated soil which was contaminated by cypermethrin, and let it degrade cypermethrin in the natural conditions. The residual quantity of cypermethrin in the soil was detected by UV spectrophotometry. After 15 days degradation rate could reach 57.67%. The results showed that the bioremediation technology of using microbe treat pesticide-contaminated soil has broad application prospects.