Chlorpyrifos degrading Pseudomonas stutzeri isolated from pesticide contaminated soil

Pesticides have been continuously used by farmers worldwide, including Thailand leading to their accumulation in agricultural soils. Bioremediation using microorganisms to degrade pesticides in soils has currently become of interest because it is considered to be cost effective and safe. The main objectives of this study were to isolate and characterize bacteria degrading chlorpyrifos, an organophosphate pesticide commonly used in Thailand. The characterization of the isolated bacteria included chlorpyrifos tolerance study. The most chlorpyrifos tolerant isolate was further subjected to the determination of a gene responsible for chlorpyrifos degradation and molecular identification. For the isolation of chlorpyrifos degrading bacteria from soils, M9 minimal medium supplemented with 100 ppm was used. Of all 6 isolated chlorpyrifos degrading bacteria, the most chlorpyrifos tolerant bacterial isolate was a gram negative bacterial isolate CHL3. It was tolerant to chlorpyrifos as high as 2,000 ppm. From plasmid isolation, it was found that the bacterial isolate CHL3 had no plasmid, indicating that a gene responsible for chlorpyrifos degradation was on the chromosome. When it was subjected to the 16S rDNA sequence analysis, it was identified as Pseudomonas stutzeri. The bacterium obtained from this study might be useful for its application in bioremediation of agricultural soils contaminated with chlorpyrifos and organophosphate pesticides.