Isolation And Immobilization Of Diethylstilbestrol-Degrading Bacteria Strain S

Environmental estrogen pollution has been the third largest environmental problems after ozone depletion and global warming, and it has been described as a time bomb to human survival. Nowadays it has become a hot issue whether microbes could be used to degrade estrogens efficiently to reduce environmental estrogen pollution.A DES-degrading bacteria strain S was isolated from activated sludge of a sewage treatment plant. The growth and DES-degrading features of strain S was studied. The immobilized conditions of strain S were optimized. The application effects of immobilized strain were evaluated preliminary. Main novel findings are shown as follows:(1) Strain S was identified as Serratia sp. based on physiological characteristics and 16S rDNA Sequence homology analysis. It could degrade 68.3% of DES in 7 days under laboratory culture conditions. Strain S was aerobic, and its optimum growth conditions were 30?, pH 7.0 and no added salt. It was observed that strain S could resist erythromycin, streptomycin, tetracycline and spectinomycin, and the low concentration of chloramphenicol and ampicillin, but it was sensitive to gentamicin and kanamycin. The optimum conditions for DES biodegradation by the obtained strain were 30?,40?60 mg·L-1 DES, pH 7.0,5% of inoculation amount, Og·L-1 of added NaCl, and 10 mL of liquid medium volume in 100 mL flask.(2) With sodium alginate as the embedding agent, immobilized strain S showed obvious superiority to free degrading bacteria. Under laboratory culture conditions, the degradation rate of immobilized strain S was 83.1%, which was 14.8% higher than free degrading bacteria. The best immobilization conditions were determined through orthogonal test, which were 4% of SA, bacterium suspension:SA 1:2,4%of CaCl2 and 6 h. The proper inoculation of immobilized strain S was 300 g·L-1, and the optimum initial concentration of DES was 20?40 mg·L-1.(3) DES was detected in a lake in Nanjing, and the detection concentrations of three sewage outfalls were 40.01,37.90 and 33.52?g·L-1, which were much higher. Immobilized strain S was added to water samples to evaluate its effect. Immobilized strain S showed good DES-degradation effects on polluted water, and the degradation rate of 7 d was over 90%. As a result, application of immobilized strain S was effective.