Rhodococcus rhodochrous K37, a Gram-positive bacterium grown under alkaline conditions, was isolated for its ability to metabolize PCBs. Analysis revealed that it has eight genes encoding extradiol dioxygenase, which has 2,3-dihydroxybiphenyl 1,2-dioxygenase activity, and these genes were designated
bphC1 to
bphC8. According to the classification of extradiol dioxygenases [Eltis, L. D., and Bolin, J. T.,
J. Bacteriol.,
178, 5930–5937 (1996)], BphC3 and BphC6 belong to the type II enzyme group. The other six BphCs were classified as members of the type I extradiol dioxygenase group. BphC4 and BphC8 were classified into a new subfamily of type I, family 3. Two linear plasmids, 200 kb and 270 kb in size, were found in K37, and the
bphC6 and
bphC8 genes were located in the 200 kb linear plasmid. Northern hybridization analysis revealed that the
bphC1,
bphC2, and
bphC7 genes were induced in the presence of testosterone, the
bphC6 gene was induced by fluorene, and the
bphC8 gene was induced by biphenyl. All eight BphC products exhibited much higher substrate activity for 2,3-dihydroxybiphenyl than for catechol, 3-methylcatechol, or 4-methylcatechol.
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