Enantioselective Dechlorination of Polychlorinated Biphenyls in Dehalococcoides mccartyi CG1

Abstract

Reductive dehalogenation mediated by organohalide-respiring bacteria plays a critical role in the global cycling of organohalides. Nonetheless, information on the dehalogenation enantioselectivity of organohalide-respiring bacteria remains limited. In this study, we report the enantioselective dechlorination of chiral polychlorinated biphenyls (PCBs) by CG1. CG1 preferentially removed halogens from the (-)-enantiomers of the three major environmentally relevant chiral PCBs (PCB174, PCB149, and PCB132), and the enantiomer compositions of the dechlorination products depended on their parent organohalides. The assays with crude cell extracts or concentrated whole cells and the experiments with living cells showed similar enantioselectivities, in contrast with the distinct enantiomeric enrichment factors (ε) of the substrate chiral PCBs. Additionally, these results suggest that concentrated whole cells might be an alternative to crude cell extracts in tests of reductive dehalogenation activities. The enantioselective dechlorination of other chiral PCBs that we resolved via gas chromatography further confirmed the preference of CG1 for the (-)-enantiomers. A variety of agrochemicals and pharmaceuticals are chiral. Due to the enantioselectivity in biological processes, enantiomers of chiral compounds may have different environmental occurrences, fates, and ecotoxicologies. Many chiral organohalides exist in anaerobic or anoxic soils and sediments, and organohalide-respiring bacteria play a major role in the environmental attenuation and global cycling of these chiral organohalides. Therefore, it is important to investigate the dehalogenation enantioselectivity of organohalide-respiring bacteria. This study reports the discovery of enantioselective dechlorination of chiral PCBs by CG1, which provides insights into the dehalogenation enantioselectivity of and may shed light on future PCB bioremediation efforts to prevent enantioselective biological side effects.

Iron acquisition system of Sphingobium sp. strain SYK-6, a degrader of lignin-derived aromatic compounds

“…A recent study has suggested that Synechocystis sp. strain PCC 6803 does not produce siderophores, and its TBDRs mediate the uptake of free iron and ferric-siderophores produced by other bacteria (xenosiderophore) 48 . In addition to all of the above, considering there are 74 TBDR-like genes in the SYK-6 genome, TBDRs of SYK-6 may mediate the uptake of free iron and xenosiderophore.…”

Insights into the Occurrence, Fate, and Impacts of Halogenated Flame Retardants in Municipal Wastewater Treatment Plants

“…More recently, Zhao et al reported a high abundance of organohalide-respiring bacteria, including Dehalococcoides , Dehalobium , Dehalobacter , Desulfitobacterium , and Sulfurospirillum , in a conventional WWTP. Debromination of PBDEs has been previously reported by at least one member of each of these genera. , These findings indicate that wastewater sludge likely contains diverse anaerobic PBDEs-debrominating microorganisms; additional work is needed to identify and characterize these microorganism as well as the biological processes responsible for anaerobic biotransformation of PBDEs in wastewater sludge.…”

“…Debromination of PBDEs has been previously reported by at least one member of each of these genera. 170,171 These findings indicate that wastewater sludge likely contains diverse anaerobic PBDEs-debrominating microorganisms; additional work is needed to identify and characterize these microorganism as well as the biological processes responsible for anaerobic biotransformation of PBDEs in wastewater sludge.…”

Spatial Distribution, Bioconversion and Ecological Risk of PCBs and PBDEs in the Surface Sediment of Contaminated Urban Rivers: A Nationwide Study in China

“…For the enantioselective analyses of chiral PCBs, two different enantioselective columns were utilized to separate PCB enantiomers as previously described. , A CP-Chirasil-Dex CB column (25 m × 0.25 mm × 0.25 μm film thickness; Agilent J&W Scientific) was used for the separation of PCB-84, PCB-91, PCB-95, PCB-132, PCB-135, PCB-136, PCB-149, PCB-174, and a BGB-172 column (30 m × 0.25 mm × 0.18 μm film thickness; Boecten, Switzerland) was used for the separation of PCB-183. The composition of chiral PCB enantiomers was quantified by using the enantiomeric fraction (EF) according to the following equation: EF = E1/(E1+E2), where E1 and E2 represented the peak areas of (+)-enantiomers and (−)-enantiomers, respectively.…”