Isolation And Characterization Of Bacterial Strains Capable Of Degrading Hexachlorocyclohexane And P-Nitrophenol

HCH(Hexachlorocyclohexane,HCH)as an organochlorine pesticide,is persistent, semi-volatile,bioaccumulation and high toxicity and is one of the first controlled persistent organic pollutants(Persistent Organic Pollutants,POPs).Because they are toxic to many living organisms and may accumulate in the food chain,nitrophenols have been rated as priority pollutants by the United States Environmental Protection Agency.P-nitrophenol (PNP)is probably the most important among the mono-nitrophenols in terms of the quantities used and potential environmental contamination.The toxicity and pollution treatment technology of PNP is an important research topic.Two bacterial strains(HY1 and HY2),capable of using PNP as a sole source of carbon and energy,were isolated from the pesticide-polluted soil.Analysis of the 16s rDNA gene sequence suggested that HY1 had a close relationship to Pseudomonas putida and was designated as Pseudomonas sp.HY1.Meanwhile,HY2 had a close relationship to Arthrobacter ureafaciens DSM 20126 and was designated as Arthrobacter sp.HY2. Unfortunately we failed to get the strain that had HCH degradation activity from soil samples.Nitrite was detectable during incubation,and was simultaneously released in stoichiometric quantities with PNP depletion.When PNP was degradated completely,the strain was at maximum growth.HY1 and HY2 had activity of degradating PNP under the conditions of 15-40℃and pH 5-10.HY1 had the highest degradation activity in alkaline pH (pH 8-10)and 30℃,while HY2 in alkaline pH(pH 7-9)and 30℃.HY2 has an unusually high substrate tolerance for PNP degradation in MSM.Effective degradation rates slowed as the concentration of PNP was increased.Addition of glucose from 0.1%to 0.5%generally enhanced the degradation of PNP at high concentration(400 mg/L)although acidification as a result of glucose metabolism had a negative effect on PNP depletion.The optimum concentration of glucose was 1 g/L.In our biodegradation system,adding different concentrations of urea did not have an impact on the growth of HY2 and the degradation of PNP.Maybe the urea is relatively stable in the alkaline conditions.β-cyclodextrin could not only shorten the extension of demurrage and enhancing effect on PNP degradation,but also increase the tolerance range of the strain to PNP.When the concentration of PNP was over the strain's tolerance range,higher concentrations ofβ-cyciodextrin had a significantly more powerful enhancing effect on PNP degradation.