Isolation, Identification And Degrading Characters Of DDT Degrading Strain KK

In this dissertation, taking DDT as a model pollutant, a strain of bacterium KK capable of highly degrading DDT was screened from the soil sample collected from a pesticide plant after taming and enrichment. Based on analysis of phenotype, physiological and biochemical characters and 16S rDNA, KK was identified as Alcaligenes sp. Degrading-bacteria enrichment and isolation, characterization of biodegradation were studied systematically. The results could be summarized as follows:1. The author introduced the use situation, pollution, mobility in environment, degradation and metabolism, ecological toxicological characteristics and pollutant management of DDT, which has been applied extensively in the world and recently in China; accordingly author presents the issues that would be investigated.2. The DDT degrading-bacteria were isolated by direct way and selective enrichment from soil exposed to pesticides and soil of pesticides production, and then researched on the bacteria in our laboratory conservation. Three high efficiently degrading strains were isolated by selective enrichment, and their degrading rates under the condition of 30℃,pH 6.0 in culture media containing 10mg·L^-1 of DDT in 3d were all above 45%. In contrast, the degrading rates of strains KK was the highest, based on analysis of phenotype, physiological and biochemical characters and 16S rDNA, KK was identified as Alcaligenes sp., we choose the strain KK for further study.3. The effects of carbon source, pH, temperature and DDT concentration on degradation was determined. The results showed that the degradation rate of DDT by KK was 66.5% in 24h. The biodegradation rates were the highest when the additional carbon source was 0.5%, pH value was 6.0, DDT concentration was 10mg·L^-1 and cultivated temperature was 30℃. The growth of bacteria increased with carbon source concentration increased, higher with pH from 6.0 to 10.0, and the highest when temperature was 30℃, DDT concentration was 10mg·L^-1.The strain could survive when DDT concentration was 300mg·L^-1 and the removed amount of DDT increased with DDT concentration.4. Analysis of the extracted metabolites. In our research, DDT metabolites were identified in the test culture medium. Most of the applied pesticide was released in the form of DDE. However, it may not be a unique DDT biodegradation pathway since the identities of a number of additional metabolites remain to be determined.