Sustainable bioproduction using phototrophic extracellular electron uptake

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Some bacteria are capable of using electricity and energy from light to fix carbon dioxide and ultimately for renewable, carbon-neutral to carbon-sequestering production of certain high value compounds. The overall goal of this project is to better understand this bioproduction process and to engineer bacteria to use this process for bioplastic and biofuel production. This project will create immersive research opportunities for students at the high school, undergraduate and graduate school levels. Microbial reduction-oxidation reactions drive matter and energy flow in the biosphere. Most microbes use soluble electron donors and acceptors, but some use solid-phase conductive substances. The underlying microbial process is called extracellular electron transfer (EET). The directionality of electron flow during EET can be either outbound, where solid-phase conductive substances are microbially reduced via reductive-EET; or inbound, where solid-phase conductive substances are oxidized via extracellular electron uptake (EEU). While reductive-EET is long studied, EEU has come to fore recently, and represents a paradigm shift in microbial biogeochemistry. This is because EEU-capable microbes can oxidize abundant solid-phase conductive substances such as minerals for microbial growth. A number of microbes can perform EEU, but only a subset of these organisms can perform phototrophic-EEU. This specialized metabolism harnesses the energy of light and electrons from solid-conductive minerals or their proxies (poised electrodes) to fix carbon dioxide. Accordingly, phototrophic-EEU represents a new metabolism to engineer for sustainable, carbon-neutral to carbon-sequestering bioproduction. To understand the environmental prevalence of phototrophic-EEU, and realize its full bioengineering potential, several fundamental knowledge gaps must be addressed. These include in-depth characterization of the electron input modules and their regulation; and the electron transfer pathways and the cellular electron sinks. Using multi-omic and transdisciplinary approaches, this project aims to fill these knowledge gaps to gain a systems-level understanding of phototrophic-EEU in the freshwater microbe, Rhodopseudomonas palustris and the marine microbe Rhodovulum sulfidophilum. The project will use synthetic biology, metabolic engineering, and material science to improve sustainable production of bioplastics and biofuels using phototrophic-EEU. Together, this project will expand our understanding of phototrophic-EEU, and explore the production of sustainable bioproducts using the phototrophic-EEU capable microbe, Rhodopseudomonas palustris. This project will also engage students from various educational levels in sustainability research.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.