Two distinct Dehalobacter strains sequentially dechlorinate 1, 1, 1-trichloroethane and 1, 1-dichloroethane at a field site treated with granular zero valent iron and guar gum. (1st November 2020)

• Record Type: Journal Article
• Authors: Yang, M. Ivy; Previdsa, Michael; Edwards, Elizabeth A.; Sleep, Brent E.
• Is Part Of: Water research. Volume 186(2020)
• Publication Date: 2020-11-01
• Subjects: Reductive dehalogenases -- Dehalobacter -- Groundwater remediation -- Chlorinated ethanes -- Zero valent iron -- 16S rRNA gene -- Quantitative PCR; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2020.116310
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: 16S and RDase genes were used to track biological dechlorination of 1, 1, 1-TCA. Two Dehalobacter populations were required for dechlorination of 1, 1, 1-TCA to CA. Cell yields were used to estimate biotic contribution to dechlorination at the site. ZVI and guar gum stimulated both abiotic and biotic 1, 1, 1-TCA dechlorination. Abstract: Chlorinated ethanes are environmental pollutants found frequently at many contaminated industrial sites. 1, 1, 1-Trichloroethane (1, 1, 1-TCA) can be dechlorinated and detoxified via abiotic transformation or biologically by the action of dechlorinating microorganisms such as Dehalobacter ( Dhb ). At a field site, it is challenging to distinguish abiotic vs. biotic mechanisms as both processes share common transformation products. In this study, we evaluated using the Dhb 16S rRNA gene and specific reductive dehalogenase genes as biomarkers for 1, 1, 1-TCA and 1, 1-dichloroethane (1, 1-DCA) dechlorination. We analyzed samples from laboratory groundwater microcosms and from an industrial site where a mixture of granular zero valent iron (ZVI) and guar gum was injected for 1, 1, 1-TCA remediation. Abiotic and biotic transformation products were monitored and the changes in dechlorinating organisms were tracked using quantitative PCR (qPCR) with primers targeting the Dhb 16S rRNA gene and two functional genes cfrA and dcrA encoding enzymes that dechlorinate 1, 1, 1-TCA to 1, 1-DCA and 1, 1-DCA to chloroethane (CA), respectively. The abundance of the cfrA - and dcrA -like genes confirmed that the two dechlorination steps were carried out by two distinct Dhb populations at the site. The biomarkers used in this study proved useful for monitoring different Dhb populations responsible for step-wise dechlorination and tracking biodegradation of 1, 1, 1-TCA and 1, 1-DCA where both abiotic (e.g., with ZVI) and biotic processes co-occur. Graphical abstract: Image, graphical abstract