Isolation Of Beta-cypermethrin Degrading Bacterium And Studies On Its Degrading Enzymes Characteristics

Pyrethroids have become one of the most widely employed insecticides in the world because of their high insecticidal activity but low mammalian toxicity,largely supplanting acutely toxic organophosphorus and organochlorine pesticides.However,continuous or excessive applications may lead to many environmental issues and potential risks to human health.Bioremediation is acknowledged as an economic,efficient,and environment riendly treatment approach to clean up pyrethroid contamination in the environment.Several studies have been conducted on the microbial degradation of pyrethriods and its major pathway of degradation has been prelimimarily demonstrated.But several microorganisms which could degrade beta-cypermethrin have been reported.A bacterium DL-4 was isolated from pyrethroid-contaminated soil of a pesticide manufactory by liquid enrichment culture,limiting concentration culture and multi plate linked method.It could utilize 100 mg/L beta-cypermethrin(?-CP)as the sole source of carbon and energy for growth,and degrade 67%of ?-CP after 5 d.Based on physiological and biochemical properties,Sherlock MIS and 16S rDNA gene sequence analysis,strain DL-4 was gram-negative,strictly aerobic,rod shaped and forming a flagellum,so the isolate was identified as Bacillus sp.Studies on degradation characteristics of Bacillus sp.DL-4 showed that the optimal fermentation conditions for degradation was 37 ? and pH 7.0.Pyrethroids degradation of DL-4 was positively influenced by the presence of the supplementary carbon sources and nutrients,and the percentage of ?-CP degradation was 85%,78%and 87.5%in the presence of glucose,tryptone and yeast extract,respectively.Strain Bacillus sp.DL-4 was also found having ability to degrade 100 mg/L cypermethrin with 65%degradation rate,but no degradation was oberserved on fenpropathrin,fenvalerate and deltamethrin.In addition,Bacillus sp.DL-4 could survive and degrade initial ?-CP concentration of 50-200 mg/L,but optimal substrate concentration was 100 mg/L,Pesticide degradation was slightly enhanced caused by incease in ventilation.Pyrethroid-degrading enzyme from cell-free extract of strain DL-4 was intracellular enzyme after purifying by organic solvents ultrasonic extraction and organic solvents method.The results showed that the temperature and pH range of the degrading enzyme activity were 40-55 ? and 6.0-8.0,and the optimal temperature and pH were 45?and pH 6.5,respectively.The enzyme was strongly activated by K2+ and Mg2+ irons,and inhibited by Ca2+ and Pb2+ irons,where as less pronounced effects were observed in the presence of Fe3+?Fe2+?Cu2+ and Zn2+ cations.