ARTICLE Biphenyl and Ethylbenzene Dioxygenases of Rhodococcus jostii RHA1 Transform PBDEs

Polybrominated diphenyl ethers (PBDEs) are a class of flame retardants that have been widely used in consumer products, but that are problematic because of their environmental persistence and endocrine-disrupting properties. To date, very little is known about PBDE degradation by aerobic microorganisms and the enzymes involved in PBDE transformation. Resting cells of the polychlorinated biphenyl-degrading actinomycete, Rhodococcus jostii RHA1, depleted nine monothrough penta-BDEs in separate assays. Extensive depletion of PBDEs occurred with cells grown on biphenyl, ethylbenzene, propane, or styrene, whereas very limited depletion occurred with cells grown on pyruvate or benzoate. In RHA1, expression of bphAa encoding biphenyl dioxygenase (BPDO) and etbAa1 and etbAc encoding ethylbenzene dioxygenase (EBDO) was induced 30to 3,000-fold during growth on the substrates that supported PBDE depletion. The BPDO and EBDO enzymes had gene expression profiles that matched the PBDE-depletion profiles exhibited by RHA1 grown on different substrates. Using the non-PBDE-degrading bacterium Rhodococcus erythropolis as a host, two recombinant strains were developed by inserting the eth and bph genes of RHA1, respectively. The resultant EBDO extensively depleted monothrough penta-BDEs, while the BPDO depleted only mono-, di-, and one tetra-BDE. A dihydroxylated-BDE was detected as the primary metabolite of 4bromodiphenyl ether in both recombinant strains. These results indicate that although both dioxygenases are capable of transforming PBDEs, EBDO more potently transforms the highly brominated congeners. The availability of substrates or inducing compounds can markedly affect total PBDE removal as well as patterns of removal of individual congeners. Kristin R. Robrocka’s present address is Exponent, Inc., 500 12th St, Oakland, CA 94607. Correspondence to: Lisa Alvarez-Cohen Contract grant sponsor: University of California Center for Water Resources Contract grant sponsor: NIEHS Superfund Basic Research Program; ES04705–19 Contract grant sponsor: Chang-Lin Tien Scholarship for Biodiversity Contract grant sponsor: Natural Sciences and Engineering Research Council of