Isolation, Identification Of A Quinclorac-degrading Bacterium QC06and Its Bioremediation For Tobacco Phytotoxicity Caused By Quinclorac

Quinclorac (3,7-dichloro-8-quinolinecarboxylic acid)is a highly selective herbicide developed by BASF (Germany), which is widely applied in controlling the paddy fields barnyard grass[Echinochloa crusgralli (L.) Beauv]. Because of unreasonably application, the residues of quinclorac in the soil leaded to phytotoxicity of the next crop species, and causing heavy economic losses. For present, there is an urgent to solve the problem of phytotoxicity which caused by the residual herbicide quinclorac.To screen microorganisms with capable of degrading quinclorac,128strains were isolated from the soil of long term applied with quinclorac and outfall sludge, sewage from the herbicide company by enrichment culture. QC06, a bacterium which was able to efficiently degrading quinclorac among128strains was obtained.Then identification of quinclorac degrading strain QC06and degradation characteristics in different condition was studied. Finally, tobacco phytotoxicity caused by quinclorac and bioremediation effect of QC06were tested by the pot experiment. The main results were as follows:1. The efficiency of128strains degradation the quinclorac were detected by HPLC method. A bacterium QC06which was able to efficiently degrade quinclorac was obtained. Base on physiological and biochemical characteristics and16S rRNA sequence homology analysis, the strain QC06was identified as Pantoea agglomerans.2. The effects of temperature, inoculation amount, pH value and initial concentration of quinclorac on degradation rate were studied by degradation characteristics test. The strain QC06could decompose95.31%of quinclorac at the7th day after inoculating under the optimal degrading conditions, i.e., inoculation amount of4%(OD600=0.060),30℃for their growth, pH7.0, initial concentration of quinclorac50mg·L-1, respectively.3. Phytotoxicity trial results showed that tobacco was extremely sensitive to the quinclorac and easily cause tobacco deformity. The dosage of quinclorac in the tobacco fields need to be controlled in less than5.0×<10-2mg·kg-1(the recommended amount of25%). The results of the bioremediation by QC06showed that:at the20th, the bioremediation effect was obvious to tobacco deformity by the strain QC06, but not obvious at the40th day and60th day.A quinclorac-degrading bacterium strain QC06was isolated, and the degradation rate was test in the laboratory and natural environment in this study. There is a certain theoretical and application value in reduction the residual phytotoxicity of quinclorac in soil.