Study On Toxicological Effect Of Atrazine On Microbe Of Black Soil

In the black soil zone of in northeast region of China, atrazine has been an important agricultural pollutant and caused black soil degeneration. Microorganism can earily predict changing process of soil environment pollution, so we chose microbes in black soil as research object in this paper. Toxicological effects of atrazine on microbes in black soil were investigated, using modern molecular biological methods, from the aspects of microbial community diversity, microbial biomass, oxidative stress and microbial DNA damage caused by atrazine. It will provide a scientific basis for effective and safe application and environmental pollution reduction of atrazine. The main results are as follows:1) We analyzed microbial community structure of black soil contaminated by atrazine, using PCR-DGGE molecular biological methods, from the two porfiles of atrazine concentration and acting time of atrazine. PCR-DGGE analysis showed that:microbial community richness (S), Shannon-Wiener index (H) and evenness (E) of black soil had no significant difference with increasing concentration of atrazine and had fluctuation tendency with the passage of time, but microbial community richness (S), Shannon-Wiener index (H) and evenness (E) were lower than the control groups, respectively, and throughout the experiment the overall trend is down. The results indicated that under the condition of atrazine stress the growth of some microbial populations in the black soil was inhibited, and microbial diversity decreased by the analysis of their bands in DGGE gel during the incubation.2) We determinated microbial biomass carbon, nitrogen and phosphorus of black soil contaminated by atrazine, using the chloroform fumigation extraction method, from the two porfiles of atrazine concentration and acting time of atrazine, and analyzed the dynamic changes of microbial biomass. The results showed that:high concentration atrazine of50mg/kg had a greater impact on microbial biomass carbon, nitrogen and phosphorus of black soil. In the end of the experiment (95d), microbial biomass carbon and nitrogen of black soil treated with high concentration atrazine of50mg/kg were lower than the control group, whereas the microbial biomass phosphorus were higher than the control group. Microbial biomass carbon, nitrogen, phosphorus had fluctuation tendency with the passage of time. Compared to the control group, microbial biomass carbon, nitrogen, phosphorus are higher than the control groups throughout the experiment. The results indicated that atrazine stimulated microbial activity of black soil.3) The effect of atrazine stress on oxidative stress enzymes in the representative bacteria E. coli K12and B. subtilis B19was investigated. The results showed that:atrazine affected the growth of bacteria and decreased bacterial growth rate. SOD, CAT, GST activities and T-AOC were induced upon exposure to atrazine, indicating that the concentration of reactive oxygen species was increased and oxidative stress induced by atrazine formed in bacteria. Oxidative stress induced by atrazine may be due to imbalance of redox potential in bacterial cells, which cause bacterial metabolic disorder.4) The interaction between atrazine and microbial DNA of northeast cold black soil was tested, using fluorescence spectroscopy and UV absorption spectroscopy. We investigated fluorescence spectra, UV absorption spectroscopy, fluorescence inhibition rate and Fo/F in the system, using ethidium bromide (EB) as fluorescent probes. The results showed that:two modes of action, electrostatic interaction and intercalation, exist simultaneously between atrazine and microbial DNA of black soil. It can change the spatial structure of microbial DNA and cause DNA double-strand break damage. The fluorescence inhibition rate increased to96%or more with the increasing concentration of atrazine, indicating that there is a strong interaction force between atrazine and microbial DNA of cold black soil and interaction force increases with the increasing concentration of atrazine.In summary, this study demonstrated that atrazine caused oxidative stress in microbes of black soil, through electrostatic interaction and intercalation between atrazine and microbial DNA of black soil, resulting in DNA damage, reduction of microbial community diversity of black soil, stimulation of microbial biomass and elevation of microbial oxidative stress enzyme activiy. The genotoxicity and the oxidative damage caused by atrazine was the important internal mechanism that could cause the change of the microbial biomass and the community structure.