We have cloned and sequenced the dit gene cluster encoding enzymes of the catabolic pathway for abietane diterpenoid degradation by Pseudomonas abietaniphila BKME-9. The dit gene cluster is located on a 16.7-kb DNA fragment containing 13 complete open reading frames (ORFs) and 1 partial ORF. The genes ditA1A2A3 encode the ␣ and  subunits and the ferredoxin of the dioxygenase which hydroxylates 7-oxodehydroabietic acid to 7-oxo-11,12-dihydroxy-8,13-abietadien acid. The dioxygenase mutant strain BKME-941 (ditA1::Tn5) did not grow on nonaromatic abietanes, and transformed palustric and abietic acids to 7-oxodehydroabietic acid in cell suspension assays. Thus, nonaromatic abietanes are aromatized prior to further degradation. Catechol 2,3-dioxygenase activity of xylE transcriptional fusion strains showed induction of ditA1 and ditA3 by abietic, dehydroabietic, and 7-oxodehydroabietic acids, which support the growth of strain BKME-9, as well as by isopimaric and 12,14-dichlorodehydroabietic acids, which are diterpenoids that do not support the growth of strain BKME-9. In addition to the aromatic-ring-hydroxylating dioxygenase genes, the dit cluster includes ditC, encoding an extradiol ring cleavage dioxygenase, and ditR, encoding an IclR-type transcriptional regulator. Although ditR is not strictly required for the growth of strain BKME-9 on abietanes, a ditR::Km r mutation in a ditA3::xylE reporter strain demonstrated that it encodes an inducer-dependent transcriptional activator of ditA3. An ORF with sequence similarity to genes encoding permeases (ditE) is linked with genes involved in abietane degradation.The pulping of wood to extract fibers used to make paper produces toxic wastewaters (23). The majority of the acute toxicity can be attributed to resin acids found in these wastewaters (18). Resin acids, a class of diterpenoids found in wood extractives, can be grouped into abietanes and pimeranes. Abietane-type acids have an isopropyl chain at the C-13 carbon atom, while pimerane-type acids have methyl and vinyl substituents at this position. Although these compounds are abundant in nature, they are problematic in the pulp and paper industry because of their unnaturally high concentrations in wastewaters. Therefore, resin acids must be removed from wastewater prior to its discharge to the environment. Biological treatment using aerated lagoons is the most common method used for detoxifying the wastewater (19). Several bacteria isolated from such biotreatment systems have been reported to use resin acids as growth substrates, and this catabolic activity appears to be widespread (22,25).Pseudomonas abietaniphila BKME-9, a bacterium isolated from a pulp and paper wastewater treatment system, is able to use dehydroabietic acid, an abietane-type resin acid, as a sole source of carbon and reductant (4). A novel three-component aromatic-ring-hydroxylating dioxygenase from this strain has been cloned and expressed (21). In strain BKME-9, dehydroabietic acid is first oxidized by an unidentified enzyme at the C-7 positi...