Comparative analysis of three tetrachloroethene to ethene halorespiring consortia suggests functional redundancy

Three anaerobic, dechlorinating consortia were enriched from different sites using methanol and tetrachloroethene (PCE) and maintained for approximately 3 years. These consortia were evaluated using chemical species analysis including distribution of dechlorination products, production of organic acids and methane, and using qualitative and quantitative PCR (qPCR), terminal restriction fragment length polymorphism (TRFLP), and denaturing gradient gel electrophoresis (DGGE) with primers specific to Dehalococcoides 16S rRNA gene sequences. TRFLP and analysis of organic acids revealed differing fermentative populations in each consortium, which were dominated by acetogens. Monitoring methane production combined with qPCR for archaea showed that complete dechlorination of PCE-to-ethene occurred in the presence and absence of methanogens. The 16S rRNA gene-based analyses demonstrated that enrichment with PCE resulted in dechlorinating communities dominated by Dehalococcoides and Dehalobacter, and that up to four different PCE-dechlorinating organisms coexisted in one consortium. Further, the DGGE analysis suggested that at least one consortium contained multiple Dehalococcoides strains. The combined analysis of 16S rRNA and reductive dehalogenase genes suggested that one consortium contained a member of the Dehalococcoides "Cornell" group with the ability to respire VC.