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Quantitative PCR confirms purity of strain GT, a novel trichloroethene-to-ethene-respiring Dehalococcoides isolate.

ABSTRACT: A novel Dehalococcoides isolate capable of metabolic trichloroethene (TCE)-to-ethene reductive dechlorination was obtained from contaminated aquifer material. Growth studies and 16S rRNA gene-targeted analyses suggested culture purity; however, the careful quantitative analysis of Dehalococcoides 16S rRNA gene and chloroethene reductive dehalogenase gene (i.e., vcrA, tceA, and bvcA) copy numbers revealed that the culture consisted of multiple, distinct Dehalococcoides organisms. Subsequent transfers, along with quantitative PCR monitoring, yielded isolate GT, possessing only vcrA. These findings suggest that commonly used qualitative 16S rRNA gene-based procedures are insufficient to verify purity of Dehalococcoides cultures. Phylogenetic analysis revealed that strain GT is affiliated with the Pinellas group of the Dehalococcoides cluster and shares 100% 16S rRNA gene sequence identity with two other Dehalococcoides isolates, strain FL2 and strain CBDB1. The new isolate is distinct, as it respires the priority pollutants TCE, cis-1,2-dichloroethene (cis-DCE), 1,1-dichloroethene (1,1-DCE), and vinyl chloride (VC), thereby producing innocuous ethene and inorganic chloride. Strain GT dechlorinated TCE, cis-DCE, 1,1-DCE, and VC to ethene at rates up to 40, 41, 62, and 127 micromol liter-1 day-1, respectively, but failed to dechlorinate PCE. Hydrogen was the required electron donor, which was depleted to a consumption threshold concentration of 0.76+/-0.13 nM with VC as the electron acceptor. In contrast to the known TCE dechlorinating isolates, strain GT dechlorinated TCE to ethene with very little formation of chlorinated intermediates, suggesting that this type of organism avoids the commonly observed accumulation of cis-DCE and VC during TCE-to-ethene dechlorination.

SUBMITTER: Sung Y

PROVIDER: S-EPMC1393247 | biostudies-literature | 2006 Mar

REPOSITORIES: biostudies-literature

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Quantitative PCR confirms purity of strain GT, a novel trichloroethene-to-ethene-respiring Dehalococcoides isolate.

Sung Youlboong Y Ritalahti Kirsti M KM Apkarian Robert P RP Löffler Frank E FE

Applied and environmental microbiology 20060301 3

A novel Dehalococcoides isolate capable of metabolic trichloroethene (TCE)-to-ethene reductive dechlorination was obtained from contaminated aquifer material. Growth studies and 16S rRNA gene-targeted analyses suggested culture purity; however, the careful quantitative analysis of Dehalococcoides 16S rRNA gene and chloroethene reductive dehalogenase gene (i.e., vcrA, tceA, and bvcA) copy numbers revealed that the culture consisted of multiple, distinct Dehalococcoides organisms. Subsequent trans ...[more]

PMID: 16517646

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Project description: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 slow-releasing electron donors can be selected to generate an electron donor-limiting environment that favors reductive dechlorination and minimizes the sulfide inhibition effect.

Dataset Information

Quantitative PCR confirms purity of strain GT, a novel trichloroethene-to-ethene-respiring Dehalococcoides isolate.

Publications

Quantitative PCR confirms purity of strain GT, a novel trichloroethene-to-ethene-respiring Dehalococcoides isolate.

Similar Datasets

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