Degradation Of Chlorimuron-ethyl And Its Effect On Microecology

Chlorimuron-ethyl, as one of the most versatile class of herbicides, was widely used in agricultural production. However, during the using process, the residual of the herbicide had badly effect on the soil, and it might cause serious problems in agricultural production process. The purpose of this study was to solve this problem by using a series of research. In our study, we isolated chlorimuron-ethyl degrading bacteria from herbicide-contaminating soil, the growth characteristics of the strains and the degradation characteristics of chlorimuron-ethyl were investigated and effects of various factors on the degradation were studied. We investigated the application effects of the strains by adding them into the herbicide-contaminating soil environment. Moreover, we studied the enzymes and microbial structures in the contaminated soil. The main results were as follows:(1)We used the soybean field soil, which was using chlorimuron-ethyl as herbicide, as research material. We gradually increased the chlorimuron-ethyl concentration in the soil to let the microbes adapt the contaminated substrate. After several domesticated culture,24strains were finally isolated, including3bacteria,7fungi and4actinomycetes. Those strains laid the groundwork for the further work. The degradation rate of chlorimuron-ethyl was mesured by using the HPLC analysis, and four strains, which had the most degradation efficiency, were further used in our study. All of the four strains could degrade more than50%of chlorimuron-ethyl. We used several methods to identify the strains, and the results showed that strain D3belong to Bacillus subtilis, strain L1belong to Bacillus cereus, strain L1belong to Bacillus megaterium, strain C4a belong to Bacillus megaterium, Trichoderma longibrachiatum. We investigated the degrading characteristics of the strains and studied the effects of various environmental factors on the degradation. Moreover, we detected the efficiency by using L3to degrade chlorimuron-ethyl in the improved conditions.(2) We used the most effective degradation strain-L3to investigate the degrading details of chlorimuron-ethyl. The results showed that the enzyme, which was responsible for chlorimuron-ethyl degrading, was intracellular enzyme. With chlorimuron-ethyl as substrate, the optimal temperature and pH for the enzyme were35℃and7.5, respectively. The enzyme was stable and high activity was maintained from pH6to10. The activity of the enzyme was inhibited by Cu2+, Ba2+and Ca2+, when the concentration of these three ions increased, the enzyme activity decreased. The enzyme activity appeared to be almost unaffected by K+and Mn2+. When the concentration of Zn2+, Fe2+and Fe3+was increased to5mM, the degrading rate decreased suddenly.(3) Chlorimuron-ethyl had great effect on all the six kinds of enzyme from the soil, and it could activate catalase, polyphenol oxidase, saccharase, dehydrogenase activity. Both catalase and polyphenol oxidase showed the highest activity at the medium term of the test, and then the stimulation effect disappeared. Saccharase got the highest activity when it was first stimulated by chlorimuron-ethyl, and then the stimulation effect decreased. Both protease and urease were inhibited by chlorimuron-ethyl. The two kinds of enzyme could be inhibited greatly at the earlier stage of the test. However, the inhibition effect disappeared at the later stage of the test. In conclusion, low concentration of chlorimuron-ethyl had little effect on the enzyme in the soil, most of the enzyme activity could be recovery at the end of the test. However, when the system contained high concentration of chlorimuron-ethyl, the enzyme activities were not easy to recover.(4) PCR-DGGE analyses indicated that the microbial community had changed significantly with adding chlorimuron-ethyl to the soil. Comparatively speaking, the low concentration of chlorimuron-ethyl had small effect on microbial community, while high concentration of chlorimuron-ethyl had great influence on microbial community. With adding chlorimuron-ethyl to the soil, the changes of relative quantities of various microbes were detected in the profiles. The quantities of some microbes increased, whereas others decreased. Some microbes maintained their populations. The consortia which could grow quickly might be responsible for chlorimuron-ethyl degradation, and more degrading strains could be found after the consortia be further analysed.