To reduce the rising and harmful greenhouse gas emissions, humanity is transitioning from fossil fuels to renewable energy sources. Yet this shift reveals another core challenge: how to store energy efficiently. Lithium-ion batteries currently dominate energy storage, but their production and disposal cause serious harm to ecosystems, and recycling remains limited. Rising demand drives environmentally costly mining that consumes an enormous amount of freshwater, draining local supplies and harming nearby communities. Microbial fuel cells (MFCs) offer a potentially eco-friendlier solution: microorganisms oxidize organic compounds in wastewater, simultaneously cleaning the stream and generating electricity. Because MFCs harvest energy from a continuous waste supply, they can sustain power generation over longer periods and with a smaller carbon footprint than Li-ion in comparable applications.
In this project, we engineer yeast MFCs with enhanced electron storage and electron transfer capacity. We achieve that goal by elevating the Saccharomyces cerevisiae intracellular NADH pool and enhancing their extracellular electron transfer. Using the CRISPR-Cas9 genome engineering tool, we deleted genes encoding the key enzymes involved in the glycerol and ethanol biosynthesis, and mitochondrial external NADH dehydrogenase, which serve as sinks of excessive cytosolic NADH through fermentation and respiration-associated pathways. Engineered strains were tested in custom MFC hardware. To fully leverage the increased intracellular NADH levels, we propose the heterologous expression of fungal cellobiose dehydrogenase (CDH) on the yeast cell surface to enhance the cell’s ability to transfer electrons to electrodes.