| A bacterial strain YN2, capable of utilizing nicosulfuron as sole carbon, was isolated from activated sludge collected from wastewater-treating system of a pesticide manufacturer. This strain was identified as Pseudomonas sp. according to its morphological, physiological and biochemical analysis and the analysis of its 16S rRNA gene sequence.The stain YN2 grew well in LB liquid medium with growth periods in logarithmic phase at the time of 3-22 h and in stable phase after 22 h. The optimum temperature and pH for the strain YN2 were 30℃ and 7.0, but when the pH was too acid or alkali, the growth of strain was distinctly inhibited. The strain could grow better when the liquid volume became smaller. The strain could grow well in NaCl solution in the range of 0-15 g·L-1, but the strain was inbibited when the concentration of NaCl is over 15 g·L-1. The optimum NaCl concentration was 15 g·L-1.In all the carbon sources, the strain could highly utilize glucose and fructose. For nitrogen source using experiments, the strain could highly utilize peptone and followed are ammonium sulfate and carbamide, while nitrite and nitrate have only little effects. The strain was resistant to chloramphenicol, ampicillin, tetracycline hydrochloride, streptomycin and carbenicillin, and was sensitive to kanamycin and gentamicin.The strain YN2 could use nicusulfuron as the sole carbon source for growth and could degrade 65.4% of 100 mg·L-1 nicusulfuron in 7 days. The optimum temperature, pH, inoculums, liquid volume and concentration for nicusulfuron degradation by strain YN2 were 30℃,7.0,5%,50 mL and 100 mg·L-1, respectively.In the tested metal ions, in the concentration at 0.1 mmo/L, Zn2+、Cu2+、Mn2+ had no influence on the degradation of nicosulfuron and Co2+ and Ni2+ could inhibit the nicosulfuron degradation efficiency. When the concentration of metal ions increased to 1 mmo/L, all the metal ions including Co2+ and Ni2+ will inhibit the nicosulfuron degradation. Orthogonal test studied the pH value, liquid volume, inoculums size and concentration on the degradation of nicusulfuron by strain YN2.The optimum pH, liquid volume, inoculums and concentration for nicusulfuron degradation by strain were 6.0,15%,50 mL and 100 mg·L-1, respectively based on orthogonal test. And the degradation efficiency of strain YN2 is 75.7% in 7 days in the optimal condition. The soil bioremediation experiment results show that:the exogenous strains YN2 can promote the degradation of nicosulfuron in the soil because the indigenous and the exogenous degradation bacteria degraded nocosulfuron in a synergy way and improved the degradation efficiency of nicosulfuron in soil.The metabolites from the degradation of nicosulfuron by strain YN2 were detected by HPLC-MS. We propose the following pathway for the biodegradation:cleavage of the the sulfonylurea bridge, yielding the corresponding 3-(dimethylcarbamoyl) pyridin-2-ylsulfonylcarbamic acid and 2-Amino-4,6-dimethoxypyrimidine. The conditions of embedding in sodium alginate immobilized strain were investigated. The results showed that when the concentration of sodium alginate was 2%, the concentration of CaCl2 being 3%, immobilized time was 4 h and the encapsulated strain mass was 5%, the mechanical strength and the mass transfer performance of the obtained immobilized beads were the best. The optimum pH, temperature and initial nicosulfuron concentration for nicusulfuron degradation by strain YN2 were 7.0,30℃ and 100 mg·L-1 respectively. The immobilized bacteria could tolerance pH and temperature in a wider range than the free bacteria. |
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