| It is well known to us that herbicide always makes a great contribution to assure a bumper crop of agricultural products.. The sulfonylureas herbicides, discovered by Dupont co., Ltd (USA) in the 1970s, have been used on an exponential increase for controlling broad-leaved weeds due to their special characteristics such as high herbicidal activity, broad action spectrum, good crop selectivity, low toxicity etc. However, continued widespread use and release of such syntheties has resulted in negative effects, not only to environment pollution but to people's health. Moreover, a few studies even evidenced that the residues of some types; of sulfonylureas could show great damages in crop rotation.Bensulfuronmethyl, one type of sulfonylureas, widely used in rice field in China and southeast Asia was selected for this study because researches made so far to evaluate the effects of sulfonylureas mainly centered on chorsulfuronmethyl, sulfometuronmethyl, metsulfurorimethyl, rimsulfon. Biological community assessments including cuturable bacteria and soil enzyme activities were carried out in laboratory condition to investigate the effects of bensulfuronmthyl at different concentrations on soil micro ecosystem. A bacterium with good capability to degrade bensulfuronmethyl was also isolated and identified in this study. These results will be useful reference to building up alert index systems in bensulfuronmethyl-polluted paddy soil, environmental quality evaluation and bioremediation of bensulfuronmethyl-polluted paddy soil. The main results are reported as follows:1. Changes, on the amounts of three aerobic and five anaerobic microbes in soil polluted with bensulfuronmethyl, were simultaneously numerated during 5-week period. Results showed that different from the fact that actinomycetes could be easily stimulated by bensulfuronmethyl, aerobic bacteria and fungi were reduced to a lower level after treatment. However, the inhibitory effects to aerobic bacteria by bensulfuronmethyl were more remarkable, for instance, the number of aerobic bacteria was inhibited maximally by 76.34% in the soil treated with 0.40 mg · kg~-1 herbicide. Anaerobic bacteria in soil samples also responded differently after bensulfuronmehyl was applied. According to the data from the experiment, the hydrolytic-fermentive bacteria were activated to a high point at first stage of treatment, while hydrogen-producing acetogenic bacteriawere reduced mostly during the metaphase. Although in general, the numbers of these two microorganisms changed distinctly during incubation phase, the concentration was determined as the minor factor in comparison with time. Methanogenic-producing bacteria could increase to a high level in soil after bensulfuronmethyl treatment, but too high herbicide concentration (4.00 mg·kg~-1) made a negative effect to their numerbers. Other microorganisms: anaerobic nitrogen-fixing bacteria and sulfate-reducing bacteria were inhibited by bensulfuronmethyl, and the higher concentrations the herbicide used, the more notable inhibitory effects appeared.2. The activities of four types of enzymes, including dehydrogease, catalase, phosphorylase and urease were also measured in this study to evaluate the effect of bensulfuronmethyl to soil environment. Different results of enzyme-activities were acquired from soil samples treated with different bensulfuronmthyl concentrations. The dehydrogease activities were simulated at 7d after bensulfuronmethyl treatment, coming up to 176.31 % -480.78% higher than that in control. A similar trend was observed that the activities of catalase and phosphorylase were simulated in soil with low doses of bensulfuronmethyl while inhibited when higher concentrations were used. Dose-effect curve with R2 value was conducted to further estimate the herbicide's toxicities to the activities of two enzymes respectively (catalase activity at 21 d and phosphorylase activity at 35d). The activity of phosphorylase was considered as an index to denote the pollution caused by bensulfuronmethy based on the conclusion that the phosphorylase activity was notably influenced by both factors (time and concentration) using analysis of ANVOA. As for urease activity, no obvious changes were found after bensulfuronmethyl treatment.3. An aerobic bacterium named BH capable of degrading bensulfuronmethyl was isolated from soil samples collected from rice field polluted by this herbicide. The cells of the strain were non-motile, non-sporulating, short-rod and gram-positive; the colonies formed on agar medium were round, smooth, sticky, white-yellow in color and of butyrous consistency. Analyses of nutritional utilization in Biolog microplates, conventional phenotypic characteristics and 16S rRNA gene squencing were consistent with assigning strain BH to a member of the genera Brevibacterium.Strain BH is more sensitive to gentamicin and amikacin than erythromycin, pencicillinum and chloramphenicol within the tested concentrations but it has a strong resistance tobenzylpenicillinum. The optimal temperature for its growth is ranging from 25°C to 35 °C and the optimal pH, 7.0~7.5. During 7-day incubation, the isolate could degraded bensulfuronmethyl from 100 mg I'1 to 70.6 mg I"1 in mineral M9 medium while exhibiting more effective degradation in the presence of yeast extract, completely removing an initial of 100 mg I"1 of bensulfuronmethyl and at best 80% of an initial of 200 mg I"1. Further studies are required to determine the potential use of the isolate in the disposal of bensulfuronmethyl residues in agriculture and industry.
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