Respiratory Vinyl Chloride Reductive Dechlorination to Ethene in TceA-Expressing Dehalococcoides mccartyi

Bioremediation of chlorinated ethenes
in anoxic aquifers hinges
on organohalide-respiring Dehalococcoidia expressing vinyl chloride (VC) reductive dehalogenase (RDase). The tceA gene encoding the trichloroethene-dechlorinating RDase
TceA is frequently detected in contaminated groundwater but not recognized
as a biomarker for VC detoxification. We demonstrate that tceA-carrying Dehalococcoides mccartyi (Dhc) strains FL2 and 195 grow with VC as an electron
acceptor when sufficient vitamin B12 (B12) is
provided. Strain FL2 cultures that received 50 μg L–1 B12 completely dechlorinated VC to ethene at rates of
14.80 ± 1.30 μM day–1 and attained 1.64
± 0.11 × 108 cells per μmol of VC consumed.
Strain 195 attained similar growth yields of 1.80 ± 1.00 ×
108 cells per μmol of VC consumed, and both strains
could be consecutively transferred with VC as the electron acceptor.
Proteomic analysis demonstrated TceA expression in VC-grown strain
FL2 cultures. Resequencing of the strain FL2 and strain 195 tceA genes identified non-synonymous substitutions, although
their consequences for TceA function are currently unknown. The finding
that Dhc strains expressing TceA respire VC can explain
ethene formation at chlorinated solvent sites, where quantitative
polymerase chain reaction analysis indicates that tceA dominates the RDase gene pool.