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The organophosphate compound, chlorpyrifos, is widely used as an insecticide. Excessive use of these pesticides is disturbing the ecosystems and using biodegradation for their removing is a persistent need. In the present study, chlorpyrifos contaminated soil samples were collected from several agricultural fields in Baghdad city and the bacterial isolates were obtained by enrichment culture technique. Based on morphological, biochemical characteristics, 24 isolates were identified as Xanthomonas sp. The effect of different concentrations (100, 200, 300, 400, 500 and 1000 ppm) of chlorpyrifos on the total viable count of the isolates and their tolerance was carried out in this study. Four isolates (KNX5, KNX12, KNX21 and KNX23) could tolerate up to 400-1000 ppm of chlorpyrifos amended in minimal salt medium plates. The isolate KNX5 demonstrated heavy growth even at the highest concentration of 1000 ppm and used for further studies. The different culture conditions like carbon sources, the concentration of chlorpyrifos, pH and inoculum densities were used to evaluate the biodegradation potential of KNX5 strain. The good carbon source for chlorpyrifos metabolizing was glucose. The most efficient biodegradation results were obtained by using the inoculum density (108 CFU/ml) and pH (8). The strain KNX5 showed a high degradation potential of chlorpyrifos (93.1%) at the concentration of 400 mg/L after 10 days of incubation. This study indicated the importance of Xanthomonas local strains as a tool of bioremediation in the contaminated soil with chlorpyrifos.
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