Bioremediation of Chlorinated Ethenes in Fractured Bedrock and Associated Changes in Dechlorinating and Nondechlorinating Microbial Populations

Pérez‐de‐Mora, Alfredo; Zila, Anna; McMaster, Michaye L.; Edwards, Elizabeth A.

doi:10.1021/es404122y

Cited by 66 publications

(71 citation statements)

References 39 publications

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“…Sulfate is common in subsurface environments and is often reported as a cocontaminant with chlorinated solvents at various concentrations (0.2 to 30 mM) (12)(13)(14)(15)(16)(17). The effects of sulfate and its reduction product sulfide on other terminal electron accepting processes have been explored in anaerobic digestion, sulfate reduction, and nitrification, as well as reductive dechlorination processes (17)(18)(19)(20)(21).…”

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confidence: 99%

“…Although successful organic-stimulated bioremediation of solvents has been observed in aquifers containing sulfate, the typical approaches involve injecting an excess of electron donor in order to deplete sulfate and to avoid competition for hydrogen between dechlorination and sulfate reduction (22,23). This approach was shown to be successful at some field sites; however, it has proven to be unsuccessful at sites with high sulfate concentrations or complex geochemical conditions (15,(24)(25)(26).…”

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“…In addition, some conflicting results due to sulfate addition, ranging from enhanced dechlorination (27,29,30) to inhibited or incomplete dechlorination (15,27,29,31,32), as well as no observed effect on dechlorination (16,25), have been reported over the past decade. A review of published field data from TCE-contaminated sites with sulfate concentrations ranging from 39 to 4,800 mg liter Ϫ1 reported the overall trend that as sulfate concentrations increased, dechlorination reactions became incomplete or delayed (26).…”

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confidence: 99%

“…A review of published field data from TCE-contaminated sites with sulfate concentrations ranging from 39 to 4,800 mg liter Ϫ1 reported the overall trend that as sulfate concentrations increased, dechlorination reactions became incomplete or delayed (26). In addition, among these previous studies, there have only been a few that used microbial communities with the confirmed presence of D. mccartyi (15,28,30,32,33) and cellular quantification has been lacking. Further work is needed to clarify the significance of sulfate concentrations on reductive dechlorination under electron donor/acceptor-limiting conditions.…”

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Effects of Sulfate Reduction on Trichloroethene Dechlorination by Dehalococcoides-Containing Microbial Communities

Mao

Polasko

Alvarez‐Cohen

2017

Appl Environ Microbiol

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In order to elucidate interactions between sulfate reduction and dechlorination, we systematically evaluated the effects of different concentrations of sulfate and sulfide on reductive dechlorination by isolates, constructed consortia, and enrichments containing Dehalococcoides sp. Sulfate (up to 5 mM) did not inhibit the growth or metabolism of pure cultures of the dechlorinator Dehalococcoides mccartyi 195, the sulfate reducer Desulfovibrio vulgaris Hildenborough, or the syntroph Syntrophomonas wolfei. In contrast, sulfide at 5 mM exhibited inhibitory effects on growth of the sulfate reducer and the syntroph, as well as on both dechlorination and growth rates of D. mccartyi. Transcriptomic analysis of D. mccartyi 195 revealed that genes encoding ATP synthase, biosynthesis, and Hym hydrogenase were downregulated during sulfide inhibition, whereas genes encoding metal-containing enzymes involved in energy metabolism were upregulated even though the activity of those enzymes (hydrogenases) was inhibited. When the electron acceptor (trichloroethene) was limiting and an electron donor (lactate) was provided in excess to cocultures and enrichments, high sulfate concentrations (5 mM) inhibited reductive dechlorination due to the toxicity of generated sulfide. The initial cell ratio of sulfate reducers to D. mccartyi (1:3, 1:1, or 3:1) did not affect the dechlorination performance in the presence of sulfate (2 and 5 mM). In contrast, under electron donor limitation, dechlorination was not affected by sulfate amendments due to low sulfide production, demonstrating that D. mccartyi can function effectively in anaerobic microbial communities containing moderate sulfate concentrations (5 mM), likely due to its ability to outcompete other hydrogen-consuming bacteria and archaea.IMPORTANCE Sulfate is common in subsurface environments and has been reported as a cocontaminant with chlorinated solvents at various concentrations. Inconsistent results for the effects of sulfate inhibition on the performance of dechlorination enrichment cultures have been reported in the literature. These inconsistent findings make it difficult to understand potential mechanisms of sulfate inhibition and complicate the interpretation of bioremediation field data. In order to elucidate interactions between sulfate reduction and reductive dechlorination, this study systematically evaluated the effects of different concentrations of sulfate and sulfide on reductive dechlorination by isolates, constructed consortia, and enrichments containing Dehalococcoides sp. This study provides a more fundamental understanding of the competition mechanisms between reductive dechlorination by Dehalococcoides mccartyi and sulfate reduction during the bioremediation process. It also provides insights on the significance of sulfate concentrations on reductive dechlorination under electron donor/acceptor-limiting conditions during in situ bioremediation applications. For example, at a trichloroethene-contaminated site with a high sulfate concentration, proper...

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confidence: 99%

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confidence: 99%

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Effects of Sulfate Reduction on Trichloroethene Dechlorination by Dehalococcoides-Containing Microbial Communities

Mao

Polasko

Alvarez‐Cohen

2017

Appl Environ Microbiol

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“…Many RDases and putative RDase sequences have been identified in D. mccartyi strains (13)(14)(15)(16)(17)(18)(19)(20)(21). To date, only a few RDases from D. mccartyi have been purified and partially characterized for their activities and substrate range, including TceA (22) and PceA (23) from D. mccartyi strain 195, and VcrA from D. mccartyi strain VS (14).…”

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Identity and Substrate Specificity of Reductive Dehalogenases Expressed in Dehalococcoides-Containing Enrichment Cultures Maintained on Different Chlorinated Ethenes

Liang

Molenda

Tang

et al. 2015

Appl Environ Microbiol

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Many reductive dehalogenases (RDases) have been identified in organohalide-respiring microorganisms, and yet their substrates, specific activities, and conditions for expression are not well understood. We tested whether RDase expression varied depending on the substrate-exposure history of reductive dechlorinating communities. For this purpose, we used the enrichment culture KB-1 maintained on trichloroethene (TCE), as well as subcultures maintained on the intermediates cis-dichloroethene (cDCE) and vinyl chloride (VC). KB-1 contains a TCE-to-cDCE dechlorinating Geobacter and several Dehalococcoides strains that together harbor many of the known chloroethene reductases. Expressed RDases were identified using blue native polyacrylamide gel electrophoresis, enzyme assays in gel slices, and peptide sequencing. As anticipated but never previously quantified, the RDase from Geobacter was only detected transiently at the beginning of TCE dechlorination. The Dehalococcoides RDase VcrA and smaller amounts of TceA were expressed in the parent KB-1 culture during complete dechlorination of TCE to ethene regardless of time point or amended substrate. The Dehalococcoides RDase BvcA was only detected in enrichments maintained on cDCE as growth substrates, in roughly equal abundance to VcrA. Only VcrA was detected in subcultures enriched on VC. Enzyme assays revealed that 1,1-DCE, a substrate not used for culture enrichment, afforded the highest specific activity. trans-DCE was substantially dechlorinated only by extracts from cDCE enrichments expressing BvcA. RDase gene distribution indicated enrichment of different strains of Dehalococcoides as a function of electron acceptor TCE, cDCE, or VC. Each chloroethene reductase has distinct substrate preferences leading to strain selection in mixed communities. Microbial reductive dechlorination and organohalide respiration play a significant role in the natural and engineered attenuation of chlorinated ethenes, such as tetrachloroethene (PCE) and trichloroethene (TCE). However, microbial dechlorination via hydrogenolysis sometimes stalls at dichloroethene (DCE) and vinyl chloride (VC) which is problematic as these intermediates are more water-soluble and more toxic than PCE or TCE, particularly VC (1). Organisms that are known to be capable of respiring chlorinated ethenes to nontoxic ethene are restricted to some Dehalococcoides mccartyi strains (2-4). The genomes of two VC-respiring Dehalococcoides isolates were described previously (5), as well as the metagenome of the VC-respiring mixed culture KB-1 (6, 7). In addition to chlorinated ethenes, some D. mccartyi strains can also dechlorinate 1,2-dichloroethane (1,2-DCA) (8), 1,2-dichloropropane (9), and a variety of chlorinated and brominated aromatic contaminants (10-12).Membrane-bound reductive dehalogenases (RDases) are key enzymes that mediate dechlorination reactions in organohalide respiring microorganisms. Many RDases and putative RDase sequences have been identified in D. mccartyi strains (13-21). To date, only a few RD...

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Organohalide-Respiring Bacteria as Members of Microbial Communities: Catabolic Food Webs and Biochemical Interactions

Richardson

2016

Organohalide-Respiring Bacteria

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Bioremediation of Chlorinated Ethenes in Fractured Bedrock and Associated Changes in Dechlorinating and Nondechlorinating Microbial Populations

Cited by 66 publications

References 39 publications

Effects of Sulfate Reduction on Trichloroethene Dechlorination by Dehalococcoides-Containing Microbial Communities

Effects of Sulfate Reduction on Trichloroethene Dechlorination by Dehalococcoides-Containing Microbial Communities

Identity and Substrate Specificity of Reductive Dehalogenases Expressed in Dehalococcoides-Containing Enrichment Cultures Maintained on Different Chlorinated Ethenes

Organohalide-Respiring Bacteria as Members of Microbial Communities: Catabolic Food Webs and Biochemical Interactions

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