Isolation And Identification Of Chlorpyrifos-degrading Bacterium And Its Biological Characters

Microbial degradation of organophosphate pesticides is of particular interest because of the high mammalian toxicity of such compounds and their widespread and extensive use. It has been relatively easy for some organophosphates such as parathion to isolate degrading bacteria. However, it has been problematic isolating a degrading strain for chlorpyrifos, which has been widely used for agricultural and household pest control since 1965. The objectives of the experiments were to isolate degrading strains from the polluted soils, characterize chlorpyrifos-degrading isolates, and investigate the pathway of degradation. The results were as follows:Thirty isolates of chlopyrifos-degrading bacteria were isolated from the soils around the wastewater outlets of chlorpyrifos-produced factories in Shandong and Heibei provinces or soils exposed to organophosphate pesticides in the fields of Beijing. All of the isolates utilized chlorpyrifos as the sole source of carbon or nitrogen, but varied in the abilities to degrading this pesticide. And among them, one isolate named JHY01 was selected for further analysis for its high degrading efficiency. This isolate was identified as Pseudomonas stutzeri by 16s rDNA sequence analysis and morphological, physiological and biochemical characters.The isolate grows well in much wider temperature and pH ranges, with 38 ℃ and 7 as the optimum. The optimal ratio in liquid fermentation is 1:1 with 1% maltose as carbon source and 1% beef peptone as nitrogen source .This strain hydrolyzed chlorpyrifos to TCP and diehylthiophophate(DETP), for TCP was detected in the liquid culture medium by HPLC. The isolate also degraded methyl parathion, cypermethrin and cyhalothrin, but not deltamethrin. And the strain degraded methyl-parathion to p-nitrophenol which was identified by GC-MS.The ability of the isolate to mineralize chlorpyrifos was investigated under different culture condition. The results suggested that chlorpyrifos concentration, inoculating quantity, culture temperature, pH and culture period had great effects on the degradation of chlorpyrifos. The rate of degradation varied between 10.94% and 100% according to different influencing factors. The strain removed 97.8% of the 100mg/L chlorpyrifos in the mineral liquid medium within 3days when the inoculating concentration reached 4.41×l0~8cfu/ml.These results highlight the isolate of this bacterium to be used in the contamination control of pesticide pollution in agricultural environment.