Isolation Of Malathion Degrading Stains And Degradation Of Malathion

The residue and pollutant of pesticides were attended by the whole world. Themalathion that are produced and used in large scale in China, has caused pollution indifferent regions of soil and water due to its widely use scope, excessive quantity andmuch larger water-solubility than other pesticides. Based on the threaten to the healthof human beings and the environment, the study of the residue and degradation ofmalathion were significantly. On the degradation of malathion, the following contentswere performed in the present thesis.1. A total of312strains degrading chlorpyrifos were screened and isolated fromsoils simulated with residual malathion for a long time.2. As the isolated312strains in selective medium plate (containing500mg·L-1malathion) did not show significantly the physiological characteristics change toindicate the degradation of malathion, gas chromatography (GC) was used todetermine the degradation activity of the isolated strains one by one. The resultsshowed that4strains, named as B20、I2、I4、L19, had ability to degrade malathion.When20mg·L-1malathion was used as the only carbon source, the degradation ratesof malathion were8.9%,15.4%,27%and87.32%for the4stains within48h,respectively.3. By morphological, physiological and biochemical characteristics of the strainB20, I2, I4and L19, were identified as Aeromonas sp, Escherichia sp, Micrococcussp and Brevundimonas sp, respectively. Strain L19was identified as Brevundimonasdiminuta according to16S rDNA sequence analysis.4. The degradation characteristics of strain L19were studied. Under thecondition of30℃, pH6.5, malathion of20mg·L-1and shaking at160r·min-1, thedegradation rate of L19strain for malathion was87.32%after cultured for48h. Thedegradation ability of strain L19on malathion was positively correlated to inoculatedamount.5. The optimal growth condition of strain L19was studied. The optimal growthtemperature and pH was studied by single-factor test, with tests of the temperaturefrom15℃,20℃,25℃,30℃to35℃, and acidity from pH6.0, pH6.5, pH7.0, pH7.5to pH8.0. Finally, the optimal growth conditions were determined as25℃and pH7.0respectively.