Isolation And Characterization Of A Novel Diphenyl Ether Degrading Bacterium And A Degrading Fungi

Polybrominated diphenyl ethers(PBDEs) are man-made flame-retardant chemicals that are widely used to decrease the flammability of plastics, electronic appliances, textiles and polyurethanes. Because of the widespread production and improper disposal of materials that contain PBDEs, there has been an increasing accumulation of these compounds in the environment. The toxicity of PBDEs are variable for different congeners with several showing neurotoxic toxicity in mice and dioxin-like endocrine disruption. Bioremediation of contaminated soil is green, economical and promising, which can make up for the deficiency of physical and chemical technology.In this study, an enrichment culture is domesticated from activated sludge of a wastewater treatment plant and high-efficiency degradation strains were isolated. The patterns of the degaradation of diphenyl ether, biphenyl and4-brominated by DE-degrading bacteria and mixed cultures were studied afterwards. We also studied the degradation of diphenyl ether by Phanerochaete Chrysosporium and the degradation product. Meanwhile the degradation of DE in the polluted soil adding the exterior microorganism was studied by lab simulation. It can provide theory basis and experience about engineering application for bioremediation of DE and PBDEs polluted sites. The main results of this research are as follows:(1) Isolation and identification of DE-degrading bacterial. An efficient diphenyl ether degrading bacterium strain DZ-3was isolated which was able to utilize DE as a sole source of carbon, nitrogen and energy under aerobic condition. In addition, the other strain CZ-3was also isolated, which can’t degrade DE but the mixed cultures of the two strains could enhance the degradation of DE compared with DZ-3culture. DZ-3and CZ-3were identified as Sphingomonas sp. DZ-3and Ochrobactrum sp. CZ-3based on16S rDNA gene sequencing.(2) The degradation properties of DE-degrading bacterium and mixed culture. Diphenyl ether degradation experiments using high performance liquid chromatograph (HPLC) showed that strain DZ-3could degrade71%of DE (initial concentration of835mg L-1) within6days, while the mixture of DZ-3and CZ-3can degrade90%within4days. To further investigate the degree of metal ions affecting the biodegradation of Sphingomonas sp. DZ-3, a background propagation artificial neural network(ANN) was used to conduct a sensitive analysis on the individual variables. The ANN model showed satisfactory fits for the experimental data. The result indicated that Mg2+appeared to be the most important metal ions for the biodegradation of DZ-3with a relative importance of31%, followed by Co2+(25.5%), Ni2+(15.1%),in which Mg2+had a positive effect on the degradation while Co2+and Ni2+had negative ones. In addition, the strain DZ-3even catabolized biphenyl and monobrominated diphenyl ether.(3) The degradation properties of DE by Phanerochaete Chrysosporium.The result showed that Phanerochaete Chrysosporium could degrade93.4%of DE (initial concentration of835mg L-1) and the production was identified as4-hydroxy-diphenyl ether. The production was toxic and could decrease the activity of Phanerochaete Chrysosporium,The enzyme catelizing the degradation was indicated to be P450by P450inhibitors.(4) The degradation of DE by bacterium and Phanerochaete Chrysosporium in lab simulation. The degradation of DE in the polluted soil adding the exterior microorganism was studied by lab simulation. The result showed that the bacterium culture and mixed culture of degrading bacterium and Phanerochaete Chrysosporium can both degraded98%of DE in the soil in6days, and the degading rate of DE by Phanerochaete Chrysosporium was40%.