Concurrent Ethene Generation and Growth of Dehalococcoides Containing Vinyl Chloride Reductive Dehalogenase Genes During an Enhanced Reductive Dechlorination Field Demonstration

Abstract

Dehalococcoides bacteria that produce catabolic vinyl chloride (VC) reductive dehalogenase enzymes have been implicated as a requirement for successful biological dechlorination of VC to ethene in groundwater systems. Therefore, the functional genes in Dehalococcoides that produce VC reductase (e.g., vcrA) may be important biomarkers for predicting and monitoring the performance of bioremediation systems treating chloroethenes via enhanced reductive dechlorination (ERD). As part of an ERD field demonstration, 45 groundwater samples were analyzed for vcrA using quantitative PCR. The demonstration delivered lactate continuously via groundwater recirculation over 201 days to an aquifer contaminated with cis-1,2-dichloroethene (cDCE, approximately 150 microM) and VC (approximately 80 microM). Ethene (approximately 4 microM) and Dehalococcoides containing vcrA (average concentration of 4 x 10(3) gene copies L(-1)) were detected a priori in the demonstration plot; however, aquifer materials in a bench treatability test were able to dechlorinate cDCE with only a 4-month lag period. Given the short (7-month) schedule for the field demonstration, the field plot was bioaugmented on Day 69 with a mixed culture (KB-1) that included Dehalococcoides containing vcrA. Stimulated ethene generation commenced within four weeks of donor addition. Ethene concentrations increased until Day 145, and reached maximum concentrations of 10-25 microM. Concentrations of vcrA increased concurrently with ethene production until Day 145, and plateaued thereafter at 10(7) to 10(8) gene copies L(-1). These results indicate simultaneous growth of Dehalococcoides containing vcrA and ethene generation in an ERD field application. The quantitative increase in concentrations of Dehalococcoides containing vcrA at this site provides further evidence that the vcrA gene is an effective biomarker for field-scale ERD systems.

Identification of abiotic and biotic reductive dechlorination in a chlorinated ethene plume after thermal source remediation by means of isotopic and molecular biology tools

“…Furthermore, assessing the presence of genes that encode for VC reductive dehalogenases (rdhA) known to catalyze VC reduction to ethene, such as vcrA, and measuring genes' mRNA level constitutes a stronger line of evidence to support complete reductive dechlorination. The vcrA and bvcA genes identified in Dhc are so far the only two functional genes described to encode VC rdhA (Krajmalnik-Brown et al, 2004;Müller et al, 2004) and their presence in field samples from sites contaminated with chlorinated ethenes was successfully related to complete dechlorination (Scheutz et al, 2008;van der Zaan et al, 2010;Damgaard et al, 2013a). It was moreover shown based on field samples that rdhA genes directly involved in dechlorination should be targeted in addition to Dhc, as different microbial species might harbour vcrA and bvcA genes due to horizontal gene transfer and are therefore also able to dechlorinate VC down to ethene (van der Zaan et al, 2010).…”

Stable carbon isotope analysis to distinguish biotic and abiotic degradation of 1,1,1-trichloroethane in groundwater sediments

“…Frequently, 1,1-DCA accumulate as a result of incomplete reductive dechlorination caused by an inadequate redox potential, the lack of available electron donor or absence of specific bacteria able to reductively dechlorinate these compounds (Scheutz et al, 2008). Theoretically, CA may be further reduced to ethane by reductive dechlorination.…”

Identification of chlorinated solvents degradation zones in clay till by high resolution chemical, microbial and compound specific isotope analysis

“…Natural and enhanced degradation of chlorinated ethenes in high permeability deposits (aquifers) is well known Major et al, 2002;Scheutz et al, 2008). In low permeability media, such as clay tills, little is known about how degradation by reductive dechlorination distributes between preferential flow paths such as sand lenses and fractures and the clay till matrix.…”