Collaborative Research: Stable Isotope-Based Differentiation of Vinyl Chloride Assimilators from Cometabolizers in Contaminated Groundwater

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1233087/1233154Mattes/CupplesVinyl chloride (VC) is a known human carcinogen and a common groundwater contaminant. This research project focuses on identifying and characterizing the key microorganisms involved in VC bioremediation at field sites. VC plumes are generated under anaerobic conditions via reductive dechlorination of chlorinated solvents, but often escape into downgradient aerobic groundwater zones. Aerobic, growth-coupled VC-oxidizing (i.e. VC assimilating) bacteria are readily isolated from VC-contaminated sites, supporting the idea that they play a role in the degradation. However, direct evidence that VC-assimilating bacteria are present and active in situ remains elusive. Further, it is unclear if VC-assimilating isolates are the dominant microbes in the subsurface or if their cultivation is a result of enrichment bias. Also, VC-assimilators cannot be distinguished from the larger related group of ethene-oxidizers, which are fortuitous VC oxidizers. To address these knowledge gaps, this research will use stable isotope probing (SIP) to differentiate VC-assimilating bacteria from bacteria that fortuitously oxidize VC (i.e. the cometabolizers). SIP involves microbial assimilation of 13C labeled substrates into nucleic acids during growth-coupled biodegradation. Following this, 13C labeled nucleic acids are analyzed to identify the organisms responsible for contaminant degradation. The central hypothesis is that SIP techniques, when used in conjunction with existing molecular tools, will differentiate between etheneotrophs and VC-assimilators in both laboratory and field-based applications. The research involves the following specific aims: i) to use soil and/or groundwater samples from VC-contaminated sites andapply DNA-SIP to reveal the presence, identity, and activity of VC-assimilating microorganisms, ii) to use both VC-assimilating and cometabolizing laboratory cultures to develop a SIP-based assay that differentiates between these closely related microbial groups and iii) to provide direct evidence that VC-assimilating bacteria are present and active in situ. Groundwater contamination by toxic pollutants is a major societal problem that threatens human health and the environment. In situ bioremediation practice hold promise for restoring groundwater to pre-contamination levels. Studies aimed at better understanding the presence, abundance and activity of biodegrading microbial communities will serve to bridge fundamental science and the practice of bioremediation. The long-term goal of this research is to advance the bioremediation field by developing molecular tools to characterize pollutant-degrading microorganisms in the environment. The research will involve the training of undergraduate and graduate environmental engineering students to apply molecular biology tools to environmental problems. The work will increase the number of underrepresented minority students and will also involve the development of K-12 outreach activities. The research will benefit society by addressing anthropogenic deterioration of water quality by groundwater pollutants.