FIG. 1.

Components and functions of BDO and proposed pathway for aerobic degradation of biphenyl (A) and organization of the bph, etb, and ebd genes (B) in Rhodococcus sp. strain RHA1. (A) The proposed electron transfer reactions and the conversion of biphenyl to benzoate and 2-hydroxypenta-2,4-dienoate are indicated. The BDO consists of three components, including a terminal oxygenase complex of large and small subunits, a ferredoxin, and a ferredoxin reductase. The complex catalyzes the dihydroxylation of biphenyl and is preferentially involved in the determination of substrate specificity. Ferredoxin and ferredoxin reductase promote electron transfer from NADH to the large- and small-subunit complex. Compounds: I, biphenyl; II, cis-(2R,3S)-dihydroxy-1-phenylcyclohexa-4,6-diene (dihydrodiol); III, 2,3-dihydroxybiphenyl (2,3-DHBP); IV, 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate (meta-cleavage compound [HOPD]); V, benzoate; VI, 2-hydroxypenta-2,4-dienoate. Enzymes: BphB, dihydrodiol dehydrogenase; BphC, 2,3-DHBP 1,2-dioxygenase; BphD, HOPD hydrolase. (B) Arrows indicate ORFs. The filled arrows represent the ORFs encoding BDO subunits. The names of the genes are indicated below the arrows. The etbA4 gene is located 6.0 kb upstream from etbA1. The bphA1, ebdA1, and etbA1 genes encode the large subunit of BDO, the bphA2, ebdA2, and etbA2 genes encode the small subunit of BDO, bphA3 and ebdA3 encode the ferredoxin, and bphA4 and etbA4 encode the ferredoxin reductase. The plasmid location of each gene segment is indicated on the right. Abbreviations: B, BamHI; E, EcoRI; H, HindIII; M, MluI; P, PstI; S, StuI.