Acetylene fuels TCE reductive dechlorination by defined Dehalococcoides/Pelobacter consortia

Acetylene (C₂H₂) can be generated in contaminated groundwater sites as a consequence of chemical degradation of trichloroethene (TCE) by in situ minerals, and C₂H₂ is known to inhibit bacterial dechlorination. In this study, we show that while high C₂H₂ (1.3 mM) concentrations reversibly inhibit reductive dechlorination of TCE by Dehalococcoides mccartyi isolates as well as enrichment cultures containing D. mccartyi sp., low C₂H₂ (0.4 mM) concentrations do not inhibit growth or metabolism of D. mccartyi. Cocultures of Pelobacter SFB93, a C₂H₂-fermenting bacterium, with D. mccartyi strain 195 or with D. mccartyi strain BAV1 were actively sustained by providing acetylene as the electron donor and carbon source while TCE or cis-DCE served as the electron acceptor. Inhibition by acetylene of reductive dechlorination and methanogenesis in the enrichment culture ANAS was observed, and the inhibition was removed by adding Pelobacter SFB93 into the consortium. Transcriptomic analysis of D. mccartyi strain 195 showed genes encoding for reductive dehalogenases (e.g., tceA) were not affected during the C₂H₂-inhibition, while genes encoding for ATP synthase, biosynthesis, and Hym hydrogenase were down-regulated during C₂H₂ inhibition, consistent with the physiological observation of lower cell yields and reduced dechlorination rates in strain 195. These results will help facilitate the optimization of TCE-bioremediation at contaminated sites containing both TCE and C₂H₂.