| Polybrominated diphenyl ethers (PBDEs) are a class of widely used flame retardants that have recently been detected in environmental samples, diverse biota, human blood serum, and breast milk at exponentially increasing concentrations. Currently, little is known about the fate of these compounds, and in particular, about the ability of microorganisms to transform them.;To study the potential for anaerobic transformation of PBDEs, various dehalogenating cultures were exposed to deca-BDE and an octa-BDE mixture to determine their ability to debrominate PBDEs. Only one culture debrominated deca-BDE to hepta- and octa-BDEs. In contrast, many cultures debrominated the octa-BDE formulation, including Dehalococcoides species, three species in the Desulfitobacterium genus and Dehalobacter restrictus. Numerous products were detected and Dehalococcoides-containing cultures produced hepta- through di-BDEs over the course of a year.;To investigate the debromination pathways of PBDEs, three different representative cultures of anaerobic dehalogenating bacteria were exposed to seven environmentally relevant congeners. The samples were analyzed using comprehensive two-dimensional gas chromatography (GCxGC) for maximal separation and identification of debromination products. The analyzed congeners were the five major components of the industrially used octa-BDE mixture as well as the two most commonly detected PBDEs in the environment, penta-BDE 99 and tetra-BDE 47. The three representative debrominating cultures evaluated were a trichloroethene-enriched consortium containing multiple Dehalococcoides species, Dehalobacter restrictus PER-K23 and Desulfitobacterium hafniense PCP-1. All studied congeners were debrominated to some extent by the three cultures and all exhibited similar debromination pathways with preferential removal of bromines in the para and meta positions. Debromination of the highly brominated congeners was extremely slow, with usually less than 10% of the total mass of PBDEs transformed after three months. In contrast, debromination of the lesser brominated congeners, such as penta 99 and tetra 47, was faster, with some cultures completely debrominating most of the tetra 47 within weeks.;To study the potential for aerobic transformation of PBDEs, the polychlorinated biphenyl (PCB)-degrading species Rhodococcus jostii RHA1 and Burkholderia xenovorans LB400 as we well as Rhodococcus sp. RR1 and the ether-degrading Pseudonocardia dioxanivorans CB1190 were exposed to mono- through hexa-BDEs. The two PCB-degrading strains transformed all of the mono- through penta-BDEs. Strain LB400 transformed one of the hexa-BDEs, while RR1 and CB1190 transformed only mono- and di-BDEs. The extent of transformation was roughly inversely related to the degree of bromination. RHA1 released stoichiometric quantities of bromide while transforming mono- and tetra-BDE congeners, while LB400 instead converted most of a mono-BDE to a hydroxylated mono-BDE.;The ability of RHA1 to degrade PBDEs changes dramatically with growth substrate, from extensive transformation by biphenyl-grown cells to limited transformation of di- and tri-BDEs by benzoate-grown cells. The biphenyl and ethylbenzene 2,3,-dioxygenase enzymes are implicated in PCB degradation. The gene expression of these enzymes matched the transformation profiles exhibited by RHA1 grown on different substrates. Recombinant strains of the non-PBDE degrading bacterium Rhodococcus erythropolis were developed containing the bphA and etbA genes which are responsible for the first step in degradation of biphenyl. Extensive transformation of mono- through penta-BDEs was seen in the etb recombinant, while transformation of only mono-, di- and one tetra-BDE was observed in the bph recombinant. These results indicate that although both gene products transform PBDEs, Etb is more active towards highly brominated congeners. |
