eFormate-mediated CO ₂ bioconversion: A modular electrochemical–microbial cascade compared across a diverse set of microorganisms

Direct electrochemical CO ₂ reduction is currently limited to a narrow range of multicarbon products due to limited multicarbon pathways on Cu surfaces. Biochemical methods, by contrast, are often slow due to the slow rate of gas–liquid mass transfer to microbial cells. To overcome the limitations of the individual processes, integrating electrochemical systems with biosynthetic processes has become a promising approach. However, only a narrow range of microbial strains has been explored in these combined systems. Here, we introduce a modular abiotic–biotic platform that allows electrochemically produced formate (eFormate) to be supplied independently to various microbial systems. A concentrated formate solution (0.87 M) was produced within 4 h using a SnO ₂ catalyst and subsequently converted into a biocompatible carbon feedstock by adjusting the pH. Based on earlier reports, we identified and evaluated 13 microbial strains known to grow on formate, 10 of which exhibited robust growth in the prepared formate solution and successfully secreted multicarbon products and important metabolic markers like acetate, ethanol, lactate, pyruvate, and polyhydroxybutyrate (PHB). This work establishes a proof of concept for a broadly applicable abiotic–biotic platform that expands the microbial design space by coupling CO ₂ electrolysis with carbon upgrading.