| Chlorimuron-ethyl,is a sulfonylurea herbicide that is used to control broad-leaved weeds and some grasses in soybean at very low application rates i.e.1-13 g ha-1.Because of their high phytotoxicity and the likelihood of their transportation in surface runoff,there is concern about their possible impact on aquatic ecosystems.Because of its low cost and high efficiency, Chlorimuron-ethyl has been used worldwide,ultimately resulting into more serious environment pollution.Microbialactivity has been deemed to be the most influential and significant cause of sulfonylurea herbicide removal and biotransformation.Microbial remediation has been deemed to be much more advantageous method than the others.So it has been animportant research item for us to exploit and utilize microbial resource to remove environment pollution.In this study,one bacterial strain capable of degrading Chlorimuron-ethyl were isolated, identified and phylogenetically analyzed.The results will be valuable to build up alert index systems in acetamiprid-contaminated upland soil and virtual utilization of acetamiprid-degrading bacterium in upland soil.The main results of this study are as follows:One soil Chlorimuron-ethyl-degrading bacteria,strain LW-3,was isolated from sludge collected from the bottom soil of a cropland which is polluted by Chlorimuron-ethyl.It can use Chlorimuron-ethyl as sole nitrogen resource rather than sole carbon resource.Based on physiological characteristics,biochemical tests and a partial analysis of the 16S rRNA gene sequence,the strain LW-3 was identified as pseudomonas sp..In addition,Strain LW-3 showed the resistance to AMP,CHL,ACH,CAZ and SXT.This bacterium could degrade 70%-80%of 50mg L-1 Chlorimuron-ethyl within 7 days.Biological properties of LW-3 were alsostudied.The optimal growth temperature and initial pH are 30℃and 7.0-8.0, respectively.The aeration had a positive effect on the growth of strain LW-3. The optimum carbon sources for LW-3 was glucose,and theoptimal nitrogen source was organic nitrogen,and the most optimal C/N（mol atom） ratio was 8/1.It grew well under conditions of 30℃-40℃and pH 7-8.Its resting cells degraded Chlorimuron-ethyl well at 30℃-35℃and pH6-8.Besides Chlorimuron-ethyl,LW-3 could also growon Sulfometuron-methyl,Pyrazosulfuron-Ethyl,Metsulfuron-methyl,Thifensulfuron-methy and sulfosulfuron using as sole nitrogen sources.The Chlorimuron-ethyl -degrading crude enzyme was extracted from LW-3 and analysis showed that it was an intracellular enzyme.It was a inductive enzyme.The best reaction system was as following:incubate 30μL crude enzyme in 3 mL PBS with a pH value 7.0 for 140 min at 30℃.The effect of temperature and pH on the crude enzyme were determined,the optimal condition of enzymatic degradation activity is 30℃and pH 6.5. Bioassay of Chlorimuron-ethyl has been conducted under laboratory conditions,with theindicator of growth inhibition of maize roots.Growth inhibition of maize roots in water samples was correlative with Chlorimuron-ethyl’s residual concentration,and the relationship between them in water sample is y=-0.0031x+0.1145,R=0.9682,and in soil sample,it is y=-0.0033x+0.1104,R=0.9575,（y means the height of the fresh roots,x means concentration of the Chlorimuron-ethyl）.The conclusion was applied to a case study of Chlorimuron-ethyl polluted soil to provide primary evidence for the bioremediation of Chlorimuron-ethyl by LW-3.The inoculation of strain LW-3 to soil treated with Chlorimuron-ethyl resulted in a higher degradationrate than in non-inoculated soil regardless of the soil is sterilized or non-sterilized.Organic carbon,opportune soil moisture and neutral or week acidic condition canstimulate strain LW-3 to degrade Chlorimuron-ethyl in soil sample.The Chlorimuron-ethyl degradation of strain LW-3 was restrained in flood condition or the soil with moisture less than 5%.In the optimum laboratory condition,the Chlorimuron-ethyl -polluted soil resumed to the safe level after 15 days of inoculation with strain LW-3.Finally, we believe strain LW-3 could be applied to bioremediation of environment,water body or soil,polluted by Chlorimuron-ethyl orsome other sulfonylurea herbicide after further investigation. |
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