Polybrominated diphenyl ethers (PBDEs) are persistent, highly toxic, and widely distributed environmental pollutants. The microbial populations and functional reductive dehalogenases (RDases) responsible for PBDEs debromination in anoxic systems remain poorly understood, which confounds bioremediation of PBDE-contaminated sites. Here we report a PBDE-debrominating enrichment culture dominated by a previously undescribed
Dehalococcoides mccartyi
population. A
D. mccartyi
strain, designated TZ50, whose genome contains 25 putative RDase encoding genes, was isolated from the debrominating enrichment culture. Strain TZ50 dehalogenated a mixture of penta- and tetra-BDE congeners (total BDEs 1.48 μM) to diphenyl ether within two weeks (0.58 μM Br
-
/d) via o
rtho
- and
meta
- bromine elimination; strain TZ50 also dechlorinated tetrachloroethene (PCE) to vinyl chloride and ethene (260.2 μM Cl
-
/d). Results of native-PAGE, proteomic profiling, and
in vitro
enzymatic activity assays implicated involvement of three RDases in PBDEs and PCE dehalogenation. TZ50_0172 (PteA
TZ50
) and TZ50_1083 (TceA
TZ50
), were responsible for debromination of penta- and tetra-BDEs to di-BDE. TZ50_0172 and TZ50_1083 were also implicated in dechlorination of PCE to TCE and of TCE to vinyl chloride/ethene, respectively. The other expressed RDase, TZ50_0090 (designated BdeA), was associated with debromination of di-BDE to diphenyl ether, but its role in PCE dechlorination was unclear. Comparatively few RDases are known to be involved in PBDE debromination and the identification of PteA
TZ50
, TceA
TZ50
, and BdeA provides additional information for evaluating debromination potential at contaminated sites. Moreover, the ability of PteA
TZ50
and TceA
TZ50
to dehalogenate both PBDEs and PCE makes strain TZ50 a suitable candidate for remediation of co-contaminated sites.
Importance
The ubiquity, toxicity, and persistence of polybrominated diphenyl ethers (PBDEs) in the environment have drawn significant public and scientific interest to the need for remediation of PBDEs-contaminated ecosystems. However, the low bioavailability of PBDEs in environmental compartments typically limits bioremediation of PBDEs and has long impeded the study of anaerobic microbial PBDEs removal. In the current study, a novel
Dehalococcoides mccartyi
, dubbed strain TZ50, that expresses RDases that mediate organohalide respiration of both PBDEs and chloroethenes was isolated and characterized. Strain TZ50 could potentially be used to remediate multiple co-occurring organohalides in contaminated systems.
Perfluorooctanoic acid (PFOA) electrochemical elimination systems usually focus on anodic processes, while the cathodic reactions are generally neglected. In this study, an anodic oxidation system aided by cathodically produced bubbles was proposed for enhanced PFOA oxidation, by simply rotating the electrode orientation by 90°with the cathode at the bottom and the anode at the top (abbreviated as AO/ Rotation). In the AO/Rotation system, hydrogen bubbles that were inevitably generated at the cathode could concentrate PFOA and bring it to the anode for further oxidation; thus, PFOA removal increased by 50% at 4.5 V/standard hydrogen electrode. The first-order rate also increased from 2.7 × 10 −2 h −1 cm −2 for anode oxidation alone to 3.8 × 10 −2 h −1 cm −2 for AO/Rotation. N 2 sparging promoted the defluorination rate from 31% to 100% (100 mL/min) at 3 h, further proving the dominant contribution of bubble enrichment. The aerosol release is negligible in this system according to fluoride mass balance. Energy consumption of this new system was only 7 kWh•m −3 •log −1 , half of that in the direct AO process. These results demonstrate that cathodically produced bubbles for improved mass transfer should be well-utilized during the reactor design for energy-efficient PFOA removal.
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