Biodegradation of dioxin by a newly isolated Rhodococcus sp. with the involvement of self-transmissible plasmids.

A newly isolated Rhodococcus sp. strain p52 could aerobically utilize dibenzofuran as the sole source of carbon and energy, and completely remove dibenzofuran at 500 mg l(-1) within 48 h. The strain metabolizes dibenzofuran by initial angular dioxygenation to yield 2,2',3-trihydroxybiphenyl. Strain p52 could also remove 70 % of 100 mg l(-1) 2-chlorodibenzofuran within 96 h and could metabolize a variety of aromatic compounds, namely dibenzo-p-dioxin, 2,8-dichlorodibenzofuran, dibenzothiophene, biphenyl, naphthalene, fluorene, phenanthrene, anthracene, carbazole, indole, xanthene, phenoxathiin, xanthone, and 9-fluorenone. Two distinct gene clusters encoding angular dioxygenases (DbfA and DfdA) were amplified and sequenced. The dbfA and dfdA gene clusters are located on two circular plasmids, pDF01 and pDF02, respectively. Both plasmids are self-transmissible; that is, they can transfer to the Gram-positive bacterium Bacillus cereus by conjugation.