| Endosulfan is a broad-spectrum cyclodiene insecticide that has been used extensively on variety of vegetables, fruits, cereal grains, and cotton as well as shrubs, trees, vines, and ornamentals. Contamination and persistence of endosulfan in aquatic and soil environments lead to accumulation in crop, tea, phytoplankton, zooplankton, fishes and vegetables. It is extremely toxic to fish and aquatic invertebrates and affects the central nervous system. These health and environment concerns have led to an interest in biodegradation and detoxification of endosulfan by microbiology.In this study, two endosulfan-degrading strains were isolated by enrichment culture and screening. Their growth characteristics, degrading abilitieswere also investigated in aqueous medium and soil. Furthermore, detoxification of endosulfan and their degrading enzymes were also studies. The main results are as follows:1. From three activated sludge samples, two bacterial strains CS5 and C7 were isolated. Based on the results of phenotypic features, physiological-biochemical properties, and phylogenetic similarity of 16S rRNA gene sequences, these isolates were designated as Achromobacter xylosoxidans CS5 and Ochrobacterum sp.. Their 16S rDNA partial sequences were deposited into the GenBank under accession EU266588 and EU647578.2. The strain CS5 could tolerate 500 mg/L of technical grade endosulfan, so it was selected for further research. The growth and degrading abilities of each pure culture for endosulfan degradation was investigated by HPLC. Under the condition of 30?C and pH 7, strain CS5 could degrade endosulfan 50 mg/L to more 80% in MM, NSM and MSM, respectively for 8 days. Effects of total inocula biomass amount, incubation temperatures, initial pH and endosulfan as the sole carbon or sulfur source were investigated to determine the optimal biodegradation conditions. Results showed that these isolates could effectively degrade endosulfan when provided as the sole carbon or carbon source, with total inocula 15%～25%, at 25℃～35℃, pH 7~9. 3. More than 74.2%α-endousulfan and73.5%β-endousulfan, respectively, were removed in soil inoculated with strainCS5 after 30 d of incubation. Therefore, endosulfan removal improved significantly in soils inoculated with strain CS5, which indicated their high potential use in bioremediation of contaminated environment.4. Possible intermediate metabolites of endosulfan biodegradation were analyzed by HPLC, and TLC. Endosulfan diol was detected as the major intermediate metabolites, the result suggest that strain CS5 might degrade endosulfan by a hydrolysis pathway.5. In the biodegradation process, the potential genotoxicities of residual endosulfan and the formed metabolites in aqueous medium and soil were evaluated using Salmonella typhimurium TA1535/pSK1002. In 8days decomposition processes, the degradation of endouslfan was accompanied by the significant decrease and final disappearance e of genotoxicity. The induction ratios decreased to 1.28 from 3.5 in MM, to 1.14 from 3.47 in NSM and to 1.15 from 3.47 in MSM after 8 days, respectively. In controls without incubation, genotoxicity decrease was negligible throughout all studies. Similarly, the degradation of endouslfan was accompanied by the significant decrease in soil after 30 days.6. SDS-PAGE and Native-PAGE analysis of the total proteins of strains under induced and noninduced cultures indicated that the degrading enzymes in strain CS5 might be constitutively expressed. Enzymetic degradation assays indicated that crude enzyme extracts could rapidly degrade 50mg/L endosulfan; they were effective at 30℃～45℃and pH 5.5～7.5, with the optimum pH 7 and temperature at 40℃. These enzyme extracts might be useful in rapid detoxification and cleanup of pesticide residues on the surface of farm produce.
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