Microbes and monitoring tools for anaerobic chlorinated methane bioremediation
Justicia-Leon, Shandra D.
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he chlorinated methanes carbon tetrachloride (CT), chloroform (CF), dichloromethane (DCM) and chloromethane (CM) are widespread groundwater pollutants that pose risks to human and ecosystem health. Although some progress has been made in elucidating the microbiology contributing to the aerobic degradation of DCM and CM, these efforts have had little impact on bioremediation practices aimed at restoring anoxic aquifers impacted by chlorinated methanes. Remaining knowledge gaps include the lack of understanding of the microbial mechanisms and pathways contributing to chlorinated methane transformations under anoxic conditions. Thus, the major goals of this research effort were to identify microbes that can contribute to the transformation of chlorinated methanes in the absence of oxygen, and to develop monitoring tools to assess anaerobic chlorinated methane bioremediation at contaminated sites. To accomplish these goals, freshwater and estuarine sediment samples from 45 geographically distinct locations, including 3 sites with reported chlorinated-methane contamination, were collected and screened for CT-, CF-, DCM- and/or CM-degrading activity. DCM degradation was observed in microcosms established with sediment materials from 15 locations, and the sediment-free, DCM-degrading enrichment culture RM was obtained from Rio Mameyes sediment. 16S rRNA-gene based community analysis characterized consortium RM, and identified a Dehalobacter sp. involved in DCM fermentation to non-toxic products. Organism- and process-specific monitoring tools were designed that target the 16S rRNA gene of the DCM-fermenting Dehalobacter sp. and the consortium’s specific 13C-DCM enrichment factor, respectively. Treatability studies using site materials that showed no chlorinated methane degradation activity demonstrated the feasibility of using CF- and DCM-degrading consortia for bioaugmentation applications. Collectively, this study expands our understanding of bacteria contributing to chlorinated methane degradation, provides new tools for monitoring anaerobic DCM degradation, and demonstrates that microbial remedies at chlorinated methane contaminated sites are feasible.