Field Evidence for Co-Metabolism of Trichloroethene Stimulated by Addition of Electron Donor to Groundwater

Abstract

For more than 10 years, electron donor has been injected into the Snake River aquifer beneath the Test Area North site of the Idaho National Laboratory for the purpose of stimulating microbial reductive dechlorination of trichloroethene (TCE) in groundwater. This has resulted in significant TCE removal from the source area of the contaminant plume and elevated dissolved CH 4 in the groundwater extending 250 m from the injection well. The δ 13 C of the CH 4 increases from -56‰ in the source area to -13‰ with distance from the injection well, whereas the δ 13 C of dissolved inorganic carbon decreases from 8‰ to -13‰, indicating a shift from methanogenesis to methane oxidation. This change in microbial activity along the plume axis is confirmed by PhyloChip microarray analyses of 16S rRNA genes obtained from groundwater microbial communities, which indicate decreasing abundances of reductive dechlorinating microorganisms (e.g., Dehalococcoides ethenogenes) and increasing CH 4 -oxidizing microorganisms capable of aerobic co-metabolism of TCE (e.g., Methylosinus trichosporium). Incubation experiments with 13 C-labeled TCE introduced into microcosms containing basalt and groundwater from the aquifer confirm that TCE co-metabolism is possible. The results of these studies indicate that electron donor amendment designed to stimulate reductive dechlorination of TCE may also stimulate cometabolism of TCE.

Proteomic and targeted qPCR analyses of subsurface microbial communities for presence of methane monooxygenase

“…This evidence supports previous findings using enzyme activity probes for MMO and microcosm experiments that intrinsic methane oxidation and TCE co-metabolism is actively occurring in the medial and distal zones of the TAN site (Sorenson et al 2000;Wymore et al 2007;Conrad et al 2010). Our detection of enzymes that are definitive for a specific degradation process is critical for accepting natural attenuation as a long-term strategy for remediating an aquifer (Madsen 1991).…”

“…The detection of pMMO and not sMMO is important for future studies involving enzyme kinetics and modeling of TCE co-metabolism at TAN and other sites. Detection of peptides from Mcr protein subunits in TAN-35 and TAN-29 provides evidence of a source of biogenic methane supporting previous stable carbon isotope analyses and PhyloChip community profile experiments (Conrad et al 2010).…”

“…In addition, peptides from Mcr protein, which is a biomarker for methanogenesis, were identified in TAN-29 2006 and TAN-35 planktonic samples which suggest a biogenic source of methane in the medial zone. Stable carbon isotope analyses of methane and DIC have shown a transition from methanogenesis to methane oxidation with distance from the source of the TCE contaminant plume (Conrad et al 2010). PhyloChip analysis from the same study also showed a shift in the structure of the microbial community with distance from the source well from bacteria involved in methanogenesis and reductive dechlorination to methanotrophic bacteria.…”

“…All planktonic samples from TAN showed the presence of peptides from subunit PmoB indicating active intrinsic methane oxidation, and TCE cometabolic potential, throughout the medial and distal zones of the TCE plume as well as outside the plume. Basalt samples from TAN-35 were capable of degrading 13 C labeled TCE in microcosm experiments (Conrad et al 2010). In addition, peptides from Mcr protein, which is a biomarker for methanogenesis, were identified in TAN-29 2006 and TAN-35 planktonic samples which suggest a biogenic source of methane in the medial zone.…”

Microbial Degradation of Some Halogenated Compounds: Biochemical and Molecular Features

“…The dehalorespiration bacteria compete with hydrogenotrophs, such as sulphate-reducers, nitrate-reducers, methanogens, acetogens, and other reducers [46,47]. Except hydrogen, other electron donors also can be used for reductive dehalogenation, ex.…”