Acclimating, Screening And Degradation Characteristics Of Pentachlorophenol-degrading Bacterium

Pentachlorophenol (PCP) has been used extensively as wood preservative, herbicide, fungicide, pesticides in agricultural and industrial production. It threatens seriously human health and natural environment due to its physicochemical characteristics. International agency for research on cancer (IARC) has listed PCP as a potential carcinogen.At present, physical, chemical and biological treatment methods have been applied in dealing with PCP. Because biological treatment technology has lower costs and less pollution, it has aroused general concern to management of PCP.Activated sludge aeration and method of density gradient were used to acclimate the sludge. Using pentachlorophenol as a sole carbon source, it was increased step by step in continuous eight weeks. Three PCP degrading bacterial strains were isolated from the activated sludge. Then, using three strains respectively degraded PCP in the inorganic salt solution. High Performance Liquid Chromatography (HPLC) analysis revealed that all of them can degrade PCP. One of them (strain A) is best for it can degrade 200mg/L PCP in 48h with the degradation rate of 98.6%. The optimum growth temperature for the stain A was 30℃, pH was 7.0, and it was halotolerant bacteria. According to the morphological, physiological and biochemical characteristics and 16S rDNA sequence, it was identified as Pseudomonas stutzeri.The optimum degrading conditions were obtained by detecting the degradation effect of PCP under different conditions of bacteria inoculation amount, the PCP inital concentration, temperature, and pH. It was observed that the optimum inoculation amount of strain A for degrading PCP was 2～3ml(108cfu/ml), the concentration of PCP was 0.2～0.4g/L, the temperature was 30℃, pH was 6.0.The plasmid of strain A was extracted by alkali splitting technique. The result showed that strain A has a plasmid about 700bp by the method of agarose electrophoresis. After the plasmid elimination experiment, we found that the toleration for strain A to PCP was decreased significantly, and the degradation efficiency was decreased to 13.7%. The plasmid transformation experiment used E.coli as receptor bacterium. Transformant can use PCP as its sole carbon source. The test of degrading PCP by transformant indicated that the degradation rate was 84.3%, lower than strain A. The result showed that this plasmid might play an important role in the degradation of PCP.