Influences Of Organic Phosphorous Chlorpyrifos On Microecosystem In Soils And Isolation, Identification, Characterization Of Chlorpyrifos-degrading Bacteria DSP3

Chlorpyrifos (CP), O, O-diethyl-O- (3, 5, 6-trichloro-2-pyridyl) phosphorothioate, a phosphorothioate insecticide, was commercially used for more than a decade, particularly to control foliar insects on cotton, paddy fields, pasture and vegetable crops. When it is applied to plants or mixed with soil, it will produce hazardous effects to the environment, especially to the ozone layer in the atmospheres. Leaching of the applied pesticide may pollute the surface /ground water, ultimately resulting in adverse effects on the biological systems. There is an increasing need to develop new methods to detect, isolate and characterize the strains playing a part in these degradation processes.The study was undertaken to look for some strains that were able to degrade chlorpyrifos. For the present work, the authors studied the effect of the bacterium DSP3 on chlorpyrifos in liquid culture and in soils, characterized the strain DSP3, and studied the ecological factors that govern chlorpyrifos degradation in soil. The mian results of the experiment are as fellows:1. It was found that influences of chlorpyrifos on the cultural microorgansisms in soil were studied based on the culture-dependent counting methods. It was found that the influences of chlorpyrifos varied on different microorganism populations in soil. The results showed that the numbers of actinomycetes were stimulated; however, aerobic bacteria and fungi were inhibited after application of chlorpyrifos. The activity of dehydrogenase was enhanced, however, urease, catalase and phosphorylase was strongly depressed.2. Three chlorpyrifos-degrading bacteria were isolated from soil samples from a vegetable plot in Huajiachi Campus of Zhejiang University, which are capable of using chlorpyrifos as sole carbon and energy sources. One of them named DSP3 was the best one on growth and chlorpyrifos degradation among the three strains. DSP3 was indentified to be belonged to Alcaligenes, with degradation rate of 94% within 14d at concentration of 100mg/kg chlorpyrifos in MM medium.3. The optimal temperature was 30°C, and the optimal pH was 8.5 for growth of DSP3 strain. As increasing chlorpyrifos content, substrate saturation appeared in medium at initial pH8.5. The effects of NH₄NO₃,(NH₄)₂SO₄,NaNO₃ and (NH4)₂HPO₄ were weaker on growth of DSP3 strain,but the degradation rate of chlorpyrifos was larger when utilized NH4NO3 as nitrogen source than utilized other nitrogen sources. Addition of yeast extraction, or peptone or glucose could promote the growth of DSP3 strain at different degree, but would arrearage chlorpyrifos degraded at first three days. When these organic compounds used up, there would be a degrading peak subsequently and all of these compounds promoted the degradation of DSP3 strain at different degree.4.Comparing to the pure culture of single DSP3 strain, the mixture of DSP3 strain and DSP11 strain had very little effective on total biomass, but could enhance the chlorpyrifos degradation rate remarkably. It could promote the degradation of DSP3 on chlorpyrifos, using chlorpyrifos as the sole source of carbon and phosphorus. DSP3 strain also could degrade chlorpyrifos more rapidly if added nitrogen source appropriately and none of phosphorus source into MM. The results showed that reducing the source of phosphorus, added the source of nitrogen and multi-strain mixture is probably more effective and feasible for bioremediation of chlorpyrifos contaminated environments.5. Some of the organophosphorus insecticides tested in the cross-feeding experiment were degraded by the isolate. All of those degraded organophosphorus insecticides have diethyl phosphorothionate side chains, which may explain the reason for their degradation. There was a phosphotriester bond in all compounds. It maybe concluded that the compounds were hydrolyzed at a phosphotriester bond. Due to its broad specificity against a range of organophosphorus compounds the isolated Alcaligenes faecalis strain possesses a great potential to be used for the remediation of highly toxic organophosphate nerve agents.