Organic wastes from agriculture, industrial wastewater treatment, and other feedstock can provide renewable sources for energy conversion or bioremediation via properly managed hydrolysis, fermentation, and respiration processes. The outputs of fermentation are organic acids, alcohols, and H₂ or methane (CH₄). Success or failure of any process where fermentation is necessary to break down a complex substrate for its further use in environmental processes, is determined by the fate of H₂ and the organic acids. These fermentation products can be used as electron donors for microbial electrochemical and dechlorinating systems. However, acetate and H₂ can also be converted to CH₄, which becomes a sink of electrons. The efficiency of routing electrons to the ideal destination is usually determined by syntrophic interactions among the different microorganisms present in the system. To exploit organic wastes as sources of carbon and electrons for bioenergy and remediation, understanding the microbial ecology and, specifically, the syntrophic relationships that develop is critical for success. Here, the PI proposes to channel electron flow through acetogenesis by promoting good syntrophies with homoacetogenic bacteria. Proper homoacetogen management will allow the use of renewable feedstock to fulfill two critical societal needs: renewable-energy production and reclaiming contaminated water. The research will evaluate the central hypothesis that the performance of ARB and dechlorinators will be enhanced when they are part of a beneficial syntrophy with homoacetogens. The work on the two systems will be complementary. For example, the studies with the MXC systems will be especially valuable for characterizing electron flow in the communities that involve homoacetogens, since the fate of electrons delivered to the anode can be tracked with high precision in real time. Knowledge gathered from the MXC systems will be applied to understanding electron flow in dechlorinating systems. Likewise, genomics-based techniques developed to characterize and quantify key microbial groups in one system will be applicable to the other, since homoacetogens, fermenters, and methanogens are common to both.

The PI will evaluate practical strategies for promoting the positive microbial interactions in MXCs and dechlorinating systems. Two strategies to be tested include the use of high concentrations of NH₄+ (e.g., as found in animal waste) and combinations of CO, CO₂, and H₂ (e.g., from synthesis gas). She will also characterize in detail the effect of these two strategies in promoting positive syntrophies that will lead to higher electron recoveries and dechlorination rates.

This research provides a novel approach to study biodegrading and bioenergy relevant mixed microbial communities. The results will provide fundamental understanding of the role of homoacetogens in electron and carbon flow in dechlorinating and ARB mixed communities. This will allow exploiting the use of complex renewable waste sources for bioenergy and bioremediation. The proposed research is transformative because it is the first comprehensive study which will take advantage of knowledge gathered from homoacetogenic microorganisms in two different systems in order to increase desired electron and carbon flows to beneficial microbial communities.

The research proposed will enhance energy and water sustainability. It will also directly impact the understanding of carbon and electron flow when organic wastes are used as sources of carbon and electrons in bioremediation and ARB microbial communities. The research developed will be applicable to many anaerobic environments where fermentation occurs; this will impact not only environmental systems but also health related ones, such as the human gut. The PI will focus on training and education of Hispanic female students and on being a role model to encourage them to pursue careers in science and engineering. She will integrate undergraduate research to the highest extent possible. High school students will work in her laboratory and present their work at Arizona's state science fair (AzSEF). Research presented at AzSEF reaches thousands of other high school students, their parents, and educators; in this way her work will reach and engage a broad audience. A pilot graduate research exchange with Mexico will be initiated as a means to provide an international research experience to graduate students.