Offshore Marine Sediment Microbiota Respire Structurally Distinct Organohalide Pollutants

Marine sediments are a major sink
of organohalide pollutants, but
the potential for offshore marine microbiota to transform these pollutants
remains underexplored. Here, we report dehalogenation of diverse organohalide
pollutants by offshore marine microbiota. Dechlorination of polychlorinated
biphenyls (PCBs) was observed in four marine sediment microcosms,
which was positively correlated with in situ PCB
contamination. Three distinct enrichment cultures were enriched from
these PCB-dechlorinating microcosms using tetrachloroethene (PCE)
as the sole organohalide. All enrichment cultures also dehalogenated
polybrominated diphenyl ethers (PBDEs), tetrabromobisphenol A (TBBPA),
and 2,4,6-trichlorophenol (2,4,6-TCP). Particularly, two enrichments
completely debrominated penta-BDEs, the first observation of complete
debromination of penta-BDEs in marine cultures. Multiple Dehalococcoides and uncultivated Dehalococcoidia
were identified in the initial sediment microcosms, but only Dehalococcoides was dominant in all enrichments.
Transcription of a gene encoding a PcbA5-like reductive dehalogenase
(RDase) was observed during dehalogenation of different organohalides
in each enrichment culture. When induced by a single organohalide
substrate, the PcbA5-like RDase dehalogenated all tested organohalides
(PCE, PCBs, PBDEs, TBBPA, and 2,4,6-TCP) in in vitro tests, suggesting its involvement in dehalogenation of structurally
distinct organohalides. Our results demonstrate the versatile dehalogenation
capacity of marine Dehalococcoidia and contribute to a better understanding
of the fate of these pollutants in marine systems.