Assessment and monitoring tools for aerobic bioremediation of vinyl chloride in groundwater

Abstract

Direct aerobic biodegradation of vinyl chloride (VC) offers a remedial solution for persistent vinyl chloride plumes that are not amenable to the anaerobic process of reductive dechlorination because of either prevailing geochemical conditions or the absence of active Dehalococcoidesethenogenes. However, tools are needed to evaluate and optimize aerobic VC bioremediation. This article describes the development and testing of two techniques-a microbiological tool and a molecular tool-for this purpose. Both methods are based on detection of bacteria that can use vinyl chloride and ethene as growth substrates in the presence of oxygen. The microbiological tool is an activity assay that indicates whether bacteria capable of degrading ethene under aerobic conditions are present in a groundwater sample. This activity assay gave positive results in the area of active VC degradation of an aerobic VC bioremediation test site. A rapid semiquantitative genetic assay was also developed. This molecular tool, based on polymerase chain reaction (PCR) detection of a gene involved in the metabolism INTRODUCTIONVinyl chloride (VC), a toxin and known human carcinogen, is a common contaminant in groundwater (Agency for Toxic Substance and Disease Registry, 2006; U.S. Environmental Protection Agency, 2000). It is produced as a daughter product of the anaerobic biodegradation of more highly chlorinated ethenes, such as tetrachloroethene (PCE) and trichloroethene (TCE) (Kielhorn et al., 2000;Smith, 1984). Although these compounds can be anaerobically transformed to the nontoxic product ethene, the process is often incomplete. This leads to VC stall, a condition in which VC concentrations that are low but greater than the regulatory standard, persist in groundwater.At contaminated sites where either geochemical conditions are not appropriate for complete anaerobic biodegradation of chlorinated ethenes or Dehalococcoides ethenogenes bacteria capable of carrying out the transformation to ethene (He et al., 2003) are not present, direct aerobic treatment may be an option. This treatment methodology depends on the presence and activity of any of a wide variety of bacteria (see Exhibit 1) that have (Coleman et al., 2002;Hartmans & De Bont, 1992;Verce et al., 2000Verce et al., , 2001. These bacteria use VC as a carbon and energy source (i.e., an electron donor), in contrast to the anaerobic biodegradation process in which Dehalococcoides use chlorinated ethenes as electron acceptors and an exogenous electron donor must often be added. The bacteria that aerobically degrade VC apparently do so by way of an assimilation pathway for ethene and are referred to as ethenotrophs (Fogel et al., 2005). This is in contrast to biodegradation schemes where VC is not a growth substrate (i.e., cometabolic or anaerobic degradation). Ethenotrophs metabolize ethene and VC by the same pathway, using these compounds as carbon and energy sources for growth. Exhibit 2 shows a simplified scheme of the predicted pathways for VC and ethene metabolism (Coleman & Sp...

Epoxyalkane:Coenzyme M Transferase Gene Diversity and Distribution in Groundwater Samples from Chlorinated-Ethene-Contaminated Sites

“…The PCR modifications employed in this study (nested and touchdown PCR) successfully amplified EaCoMT genes from environmental samples, but the results should be interpreted carefully with respect to PCR bias. The F131/R562 primers used in nested PCR were developed with etnE sequences from VC-assimilating Mycobacterium isolates (47) and are less degenerate than the CoMF1L/R2E primers, which were based on EaCoMT sequences from Mycobacterium sp. strain JS60, Gordonia B-276, and Xanthobacter Py2.…”

“…The first round of PCR utilized the CoMF1L and CoMR2E primer set (0.2 M each; see Table S2 in the supplemental material) as described previously (36) and 1 l of DNA extract (containing 0.14 to 15.7 ng template) ( Table 1). A subsequent round of nested PCR was performed with F131 and R562 primers (0.2 M each; see Table S2 in the supplemental material) (47) The potential that nested and touchdown PCR could introduce lower apparent gene diversity was investigated by constructing a pooled sample of DNA (referred to as AUS39) extracted from five different monitoring wells at the Australia site (i.e., samples 39-1, 39-3, 39-6, 39-7, and 39-8). DNA from AUS39 was amplified with three methods: conventional PCR, nested PCR, and a combined touchdown PCR-nested PCR.…”

Elucidating carbon uptake from vinyl chloride using stable isotope probing and Illumina sequencing

“…The site was contaminated by disposal of material containing PCE at a landfill in 1986, which ultimately resulted in a large, dilute VC plume. Remediation efforts for the plume have involved oxygen and ethene injections and have been described previously (Begley et al 2009(Begley et al , 2012Chuang et al 2010;. The groundwater from these wells was composited; 1 L was shipped to the University of Iowa, where it was stored at 4°C in the dark.…”

Oxygen and Ethene Biostimulation for a Persistent Dilute Vinyl Chloride Plume

“…Our initial microcosm studies demonstrated ethene‐stimulated VC‐metabolizing activity in mixed site groundwater. We also used a semiquantitative whole‐cell PCR assay (Begley et al 2009) to detect the presence of the epoxyalkane coenzyme M transferase gene, EaCoMT, which has been implicated in aerobic growth on both ethene and VC (Coleman and Spain 2003). The PCR test was applied to groundwater samples obtained from the site in June of 2007 and 2008, as previously reported (Begley et al 2009).…”

“…We also used a semiquantitative whole‐cell PCR assay (Begley et al 2009) to detect the presence of the epoxyalkane coenzyme M transferase gene, EaCoMT, which has been implicated in aerobic growth on both ethene and VC (Coleman and Spain 2003). The PCR test was applied to groundwater samples obtained from the site in June of 2007 and 2008, as previously reported (Begley et al 2009). EaCoMT positive colonies were found in each well, with wells undergoing active treatment having higher numbers of positive colonies, consistent with microcosm and biomass results.…”