Isolation, Characterization, Hydrophobicity And Mineralizing Mechanism Of Beta-cypermethrin Degrading Strains

Beta-cypermethrin is one of the most widely used insecticides belonging to the synthetic pyrethroid group; its wide contamination to the environment has given rise to much public concern. Several studies have been conducted on the microbial degradation of beta-cypermethrin; its major pathway of degradation has been prelimimarily demonstrated. However, no microorganisms that could completely mineralize beta-cypermethrin efficiently have been reported to date.In this study, three beta-cypermethrin-degrading strains were isolated by enrichment culture and screening. They could grow on beta-cypermethrin as the sole carbon and nitrogen sources. Their growth characteristics, degrading abilities and mineralizing mechanisms were also investigated. Furthermore, the relationship between cell surface hydrophobicity and the degradation ability were also studied. The main results were as follows:1. From activated sludge samples, three bacterial strains JC1, CH7 and JCN13 were isolated. Based on the results of phenotypic features, physiological-biochemical properties and phylogenetic similarity of 16S rDNA gene sequences, these isolates were designated as Serratia sp. JC1, Pseudomonas aeruginosa CH7 and Serratia sp. JCN13. Their 16S rDNA partial sequences were deposited into the GenBank under accession No. FJ009445, FJ009446 and FJ009447, respectively.2. Each pure culture could effectively degrade beta-cypermethrin with total inocula biomass 0.1~0.3g/L, at 20~38°C, pH 6~9 and initial beta-CP 25~1000 mg/L. Box-behnken design and response surface methodology (RSM) were used to optimize degradation conditions of the two strains. Their optimal degradation conditions were biomass 0.15g/L, T 31℃, pH 7.6(strain JC1); biomass 0.15g/L, T 29.4℃, pH 7.0(strain CH7) and biomass 0.15g/L, T 34℃, pH 8.0(strain JCN13), separately.3. The growth and degrading abilities of each strains for the beta-cypermethrin degradation were investigated by UV-Vis, TLC, HPLC, GC-FID and GC-MS. Under their optimum degrading conditions, strain CH7 could degrade 65% and 90% beta-cypermethrin(100mg/L) within 4 days and 12 days, separately; strain JC1 could degrade 92% beta-cypermethrin(100mg/L) within 10 days and mainly metabolize it within 12 days; strain JCN13 has higher degradation ability than strain JC1, it could degrade 89% beta-cypermethrin(100mg/L) within 4 days and completely mineralize it within 7 days.4. There was a fact that isomers transformation of cypermethrin in the process of beta-cypermethrin biodegradation by GC-MS analysis. Beta-cypermethrin was not directly degraded by strains, but transformed into another two low efficient isomers of cypermethrin and then all of them was completely degradated. It means that the isomers transformation coexisted with the beta-cypermethrin degradation by microbes.5. During bacteria growth of the two strains and beta-CP degradation, the time curves of cell surface hydrophobicity(CSH) were plotted respectively. The results indicated that the hydrophobicity of Serratia spp. JC1 and JCN13 associated with the concentration and toxicity of beta-CP and the bacteria growth. Obviously, strain JCN13 not only had higher hydrophobicity but also had stronger degradation ability than strain JC1. The results in this study suggested that there was a direct relationship between high CSH and strong degradation ability.