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

Abstract

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 B-12 (B-12) is provided. Strain FL2 cultures that received 50 mu g L-1 B-12 completely dechlorinated VC to ethene at rates of 14.80 +/- 1.30 mu M day(-1) and attained 1.64 +/- 0.11 x 10(8) cells per mu mol of VC consumed. Strain 195 attained similar growth yields of 1.80 +/- 1.00 x 10(8) cells per mu mol 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.