| The dissertation is composed of two parts, the studies on microbial toxicology caused by quinclorac, bensulfuron-methyl and their mixture and on microbial degradation of quinclorac bensulfuron-methyl.1. To analysis whether and how antioxidant enzymes in bacteria responded to virulence caused by quinclorac or bensulfuron-methyl, the superoxide dismutase (SOD) and catalase activities in quinclorac-degrading effectively strain Stenotrophomonas maltophilia WZ2 and Gram negative representative Escherichia coli K12 were characterized and quantified using spectrophotometric methods and native polyacrylamide gel electrophoresis (PAGE) followed activity staining. Results showed Mn-SOD and two additional catalase isozymes were induced by quinclorac or bensulfuron-methyl in 5. maltophilia WZ2, but no new type of SOD or catalase was induced in E. coli K.12. In exponential-phase cells of both strains studied, SOD activity was induced by quinclorac and bensulfuron-methyl with various concentrations, while no significant increase of catalase was observed. Both SOD and catalase activities increased in 5. maltophilia WZ2 cells treated with herbicides at stationary phase, but catalase level unvaried in E. coli K12. Quinclorac showed to be a more sensitive inducer for SOD synthesis while bensulfuron-methyl for catalase, and their mixture paid a similar effect on antioxidant enzymes as quinclorac. Antioxidant properties of two strains involved indicate that catalase has a limited role in the defense against oxidative stress induced by quinclorac or bensulfuron-methyl, whereas superoxide dismutases could be critical.2. Strain LS capable of degrading both quinclorac and bensulfuron-methyl was isolated from the soil in a herbicide manufactory. The almost complete 16S rDNA sequences (1 411 bases compared) of LS was 100% similar with representatives of genus Ochrobactrum, indicating that LS is a strain of Ochrobactrum. Phylogenetic analysis using neighbour-jioning (NJ) treeing algorithms and bootstrap evaluation with the software of MEGA showed LS is most closely related to the type strain of Ochrobactrum anthropi. Results of physio-biochemical properties analysis with Vitek auto microbic system (AMS) and Biolog microbial identification system showed 99% similarity and a similarity index of 0.345 between LS and O. anthropi, respectively, confirming LS is a strain of O. anthropi most probably. However, no flagellum was observed in the test of flagellum staining and electron microscope observation of strain LS, which is out of accord with previous reports.Strain LS could decompose 90% quinclorac and 67% bensulfuron-methyl when single kind of herbicides was used as the sole carbon source, and decompose 95.2% quinclorac and 67.5% bensulfuron-methyl when mixed herbicides quinclorac bensulfuron-methyl as the sole carbon source. High linearity correlativities between strain LS growth and single herbicide degradation were observed, with correlation coefficients of 0.9859 for quinclorac and 0.9471 for bensulfuron-methyl, respectively. Whereas, when mixed herbicide as carbon source, both correlation coefficients between strain LS growth and quinclorac or bensulfuron-methyl degradation decreased, from 0.9859 to 0.9123 and 0.9471 to 0.7869, respectively. Whole cell protein SDS-PAGE maps of LS strain induced by quinclorac, bensulfuron-methyl and their mixture displayed special bands, which might be relative with degradation and detoxification of relative herbicides in strain LS.Strain LS was also able to degrade some other herbicides and aromatic compounds, including phenol, hydroquinone, dihydroxybenzene, benzoicum acid, propisochlor, MCPA-NA, imazethapyr and tricyclazole, etc. Strain LS was sensitive to chloramphenicol (240μg·mL-1), erythromycinwhile (240μg·mL-1), amikacin (80μg·mL-1), clindamycin (480μg·mL-1), while was insensitive to cephalosporin (960μg·mL-1), ampicillin (1200μg·mL-1), penicillin (640μg·mL-1), gentamycin sulfate (60μg·mL-1).The optimal temperature for strain LS growth is 37℃. Strain LS grows well at pH 6 to 9 and had highest degradation level at initial pH 7 and 8 of medium for quinclorac and bensulfuron-methyl, respectively. Supplement of 0.00625 g·L-1 manganese ion, 0.005 g·L-1 zinc ion, 0.003 g·L-1 iron ion, 0.001 g·L-1 cobalt ion and 0.01 g·L-1 calcium ion was most available for growth of strain LS, and addition of 0.25 g·L-1 yeast extract could speedup the growth of strain LS and increase the degradation rate of quinclorac and bensulfuron-methyl by the strain.
|
PDF Full Text Request