Biodegradation Of Dioxin By Rhodococcus Sp. Strain P52

Dioxins include polychlorinated dibenzo-p-dioxin (PCDDs) and polychlorinated dibenzofuran (PCDFs) are widespread environmental pollutants which were the contaminating by-products formed during the manufacture of pesticides or the incineration of industrial and domestic wastes. They can cause a wide range of serious health effects. The conventional physical and chemical treatment methods for dioxins are diseconomy since the complex of the equipments and costly energy. Microorganisms play important roles in the degradation and mineralization of dioxins in natural environments as their wide distribution, generally adapt to variety conditions and versatile catabolic ability which will be very suitable for environmental pollutants degradation or mineralization and incomparable to any other methods.In this study, a new dibenzofuran-degrader, strain p52was isolated from the soils which were polluted by crude oil and identified as a Rhodococcus sp. on the basis of its16S rRNA gene sequence. Strain p52could aerobically utilize dibenzofuran as the sole source of carbon and energy, and completely remove dibenzofuran at500mg/L and dibenzo-p-dioxin at250mg/L within48h. Besides dibenzofuran, about70%of100mg/L2-chlorodibenzofuran was removed within96h and39%of100mg/L2,8-dichlorodibenzofuran could be removed within60h. It was also able to metabolize a variety of aromatic compounds, such as dibenzothiophene, biphenyl, naphthalene, phenanthrene, anthracene, fluoren, and carbazole. The strain metabolizes dibenzofuran by initial angular dioxygenation and characterized with the products of2,2’,3-trihydroxybiphenyl and gentisic acid. Two distinct gene clusters encoding for dioxygenase with different substrate range for these aromatic compounds were amplified and sequenced, which share high homology with two conserved gene clusters(dfdA and dbfA) for angular dioxygenase distributed in some actinomycetes strains. Several plasmids harboring in strain p52were isolated with alkaline lysis method and detected by PFGE. The two gene clusters for two dibenzofuran dioxygenases were detected to be located on plasmids pDF01and pDF02respectively. The plasmids pDF01and pDF02were self-transmissible, which could conjugatively transfer to the Gram positive bacteria, such as Bacillus cereus. Thus, Rhodococcus sp. strain p52exhibited versatility and application potential in removal of dioxin and other aromatic compounds in environment.