Uncovering novel microbial ecological relationships that foster enhanced pollutant biodegradation rates in contaminated groundwater systems

Vinyl chloride (VC) is a known carcinogen and common groundwater pollutant that may negatively impact drinking water supplies. Although some bacteria are known to remove VC from groundwater, little is known about the ecology of these organisms, especially under the low oxygen conditions that often occur in groundwater. An improved fundamental understanding of the interactions between these organisms, as well as interactions with other bacteria in the ecosystem may lead to the development of novel remediation strategies. The proposed work will benefit society by developing more precise and sustainable remediation strategies based on microbial ecology. Additional broader impacts include the training of undergraduate and graduate students to apply microbial ecology tools to environmental problems, increasing the participation of underrepresented groups in engineering, sharing research findings with environmental professionals and regulators, and providing research opportunities to high school students interested in pursuing Science, Technology, Engineering, and Math (STEM) topics. If successful, this research will provide valuable tools to help ensure the Nation's water security.<br/><br/>VC is typically generated by incomplete anaerobic biodegradation of the widely used chlorinated solvents tetrachloroethene and trichloroethene. Because anaerobic VC dechlorinating bacteria, and oxygenic nitrogen-cycling bacteria generate products that can be useful as primary and cometabolic substrates and electron acceptors for VC-oxidizers, it is hypothesized that there are novel ecological relationships between these microbial groups at oxic/anoxic interfaces or in regions of low-level oxygen flux at VC contaminated sites. This research will probe the interactions between aerobic VC-oxidizing bacteria and anaerobic VC-dechlorinating bacteria at low oxygen fluxes in contaminated groundwater environments to identify potential significant positive impacts of these interactions on VC biodegradation rates. The investigations will include three specific tasks: 1) Demonstrate simultaneous oxidation and reduction of VC in laboratory microcosms; 2) Investigate spatial relationships between VC-oxidizers, anaerobic VC-dechlorinators, and potential oxygen-producing bacteria in sediment samples from a VC-contaminated site; and 3) Investigate potential interspecies oxygen transfer relationships in low dissolved oxygen (DO) laboratory microcosms. Field samples will be analyzed by quantitative PCR and fluorescence in situ hybridization-confocal scanning laser microscopy to study spatial relationships between VC-oxidizers, anaerobic VC-dechlorinators, and potential oxygen-producing bacteria in sediment samples. Microcosm studies, including the use of oxygen permeation tubes to create low-DO flux conditions, will be used for modeling the interactions between these organisms. Finally, oxygen stable isotopes will be employed to investigate potential interspecies oxygen transfer relationships in microcosms. This project should reveal the important roles that aerobic and oxygenic nitrogen-cycling microorganisms play in mediating subsurface biodegradation reactions. An improved understanding of the contribution of aerobic processes to VC biodegradation rates will spur the transformative development of predictive quantitative relationships between the diverse microbial communities and VC attenuation. Improvements in management of groundwater contaminated with chlorinated solvents could be realized by developing more sustainable and precise approaches to remediation that involve more targeted electron donor/acceptor injections or developing bioaugmentation cultures capable of enhanced VC biodegradation. This improved understanding of aerobic biodegradation processes in subsurface systems could also extend to compounds beyond the chlorinated ethenes, as oxygenic and low oxygen flux scenarios are relevant to a variety of subsurface biodegradation processes.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.