Isolation And Identification Of Atrazine-Degrading Bacteria And Degradation Characterization

Atrazine (referred to as AT) is a selective long residual period of herbicide with a stability benzene ring. In this research,15 atrazine-degradating strains were separated from 12 soil samples and 1 water sample from the seven provinces in China. The isolated strains were divided into three categories by identification of molecular biology, physiological and biochemical:The first category including 4 strains was Arthrobacter sp., among which the YS, SYM1(Y) and CS5 were Arthrobacter ureafaciens and the SH was A.aurescens. The degradation rates of the first category strains to AT were more than 98%. The second category including DY6, DY4, DY3(C), AS, KM(B) and KM4 was Klebsiella pneumoniae. The degradation rates of the second category strains to AT were between 56% and 71%. The third category including MJ2, SYM1(W), SYM2, CS4 and CS1 was Agrobacterium sp. Those strains could restore Nitrate and Nitrite, reduce 3-keto lactose and grow without auxin and amino acid. The degradation rates of the third category strains to AT were below 5%.The environmental pH value, temperature, metal ions and carbon sources had influence on the biodegradability to AT of Arthrobacter ureafaciens YS and of Klebsiella pneumoniae AS. At the condition of pH7.0 and 28℃, the time of degradating 100mg·L-1 AT was 168 h in the strain AS and was 84 h in the strain YS. The optimum degradation conditions for the strain AS was pH7.0 and 37℃, and glucose could increase its efficiency; The optimum degradation conditions for the strain YS was pH8.0 and 25℃. Fructose, glucose and lactose could increase the efficiency of its degradation, but metal ions had different effects on the degradation efficiency.Except atzA gene, TrzN and atzB, atzC genes were amplified from Arthrobacter ureafaciens YS genomic DNA and the research showed that this set of genes were on the chromosome. Only TrzN gene was amplified from the strain of Klebsiella pneumoniae AS genomic DNA. The expression vector of TrzN gene was built using the plasmid PHY300PLK which could shuttle between Escherichia coli and Bacillus sp. After the vector was introduced, it could express the AT chlorine hydrolase gene and the E coli obtained the AT biodegradability.The research of the environmental conditions on resting cells biodegradability of the AT degrading strain YS showed:The ions of Cu2+ significantly inhibited AT-degradation, while the ions of Mg2+ significantly promoted AT- degradation; The buffer solution significantly inhibited AT- degradation; The optimum degradation temperature was 25℃in the MgCl2 reaction system but it was 25℃～37℃in the BSM reaction system. Aerobic conditions, the resting cell of the strain YS could increase biological degradation to AT.The soil respiration and soil protease was stimulated by AT, whereas the activities of soil urease were inhibited. Strain YS had a significant effect on soil respiration and soil enzyme activity of AT contaminated soil. The CO2 emission quantity was promoted and soil protease activity and urease activity were increased by bacterium.