Isolation And Characteristics Of A Dimethoate-degradation Bacterium

Dimethoate are widely used for insects control in many countries. However it caused serious problems to the environment and agricultural products because of its toxicity and refractoriness, which has become a public concern. Degradation of pesticides by microorganism is one of the most important methods.A Dimethoate- resisting bacterium XI—11, identified as Pseudomonas cichorii,w&s isolated from the soil around pesticide factory, where pesticide-polluted waste water passed through frequently. It was a high dimethoate-resisting bacterium which still showed tolerance when the concentration of dimethoate was up to 8g/L in separate substrate. The strain was unable to use dimethoate as the sole carbon source for growth. The optimum temperature for growth was 30°C while the optimum pH was 6.8 in LB medium. It was resistant to ampicillin, erythromycin, streptomycin.In this study, sodium citrate, a -ketoglutaric, succinic, malic acid, aspartic and glutamic acid as cometabolism materials facilitated degradation, so the degradation route was related to tricarboxylic acid cycle (TCA). Degradation rate was proportional to sodium citrate, NH4N03, KH2PO4 concentration to some extent, but a little higher concentration of them may inhibit the degradation. The optimum content of citrate sodium(1.10%),NH4N03 (0.043%) and KH2PO4 (0.090%) was obtained by the method of quadratic regressive revolution design. The regression model of degradation was estimated in which the square of carbon content and nitrogen content had extremely significant influence on degradation.. XI-11 can degrade 74. 28% dimethoate(200mg/L )within a week at 30°C with shaking (150r/min) o The preferable condition of degradation was as follows: 30°C, pH=6. 8~8, inoculate quantity 12%. The organism also can degrade other organophosphate pesticides such as methamidophos, omethoate and trichloroform.Three large plasmids were isolated and detected in strain XI-11 by using alkali lysis extraction and agarose gel electrophoresis. After transfer of culture for 20 generations without dimethoate as selection pressure , plasmids was still maintained and the bacterium still can degrade dimethoate. When the plasmids were partly deleted by treatment of OA and EB , the bacterium still had the ability of degrading dimethoate. The plasmid of XI-11 can be transformed...