The role of exogenous electron donors in steering microbial electrosynthesis of multi-carbon fatty acids from carbon dioxide.

Microbial electrosynthesis (MES) enables CO2 conversion to multi-carbon fatty acids, but selective upgrading to longer-chain products remains limited by inefficient electron supply. This study developed a sequential MES platform using short-chain alcohols (ethanol, propanol, isopropanol) as exogenous electron donors to direct CO2 conversion into C4-C6 fatty acids. Ethanol preferentially promotes the formation of butyrate (C4, 0.42 g/L) and caproate (C6, 0.13 g/L), whereas propanol shifts selectivity towards valerate (C5, 0.51 g/L), while isopropanol exhibits lower chain-elongation efficiency. These trends demonstrate that the carbon skeleton of the electron donor governs elongation pathways and product distribution. Predicted functional profiling and microbial community analyses indicate a higher genetic potential for key chain-elongation pathways in ethanol-fed systems, consistent with improved electron transfer and altered metabolic flux distribution. Collectively, this study establishes short-chain alcohol supplementation as an effective strategy to modulate carbon flux and selectively synthesize multi-carbon fatty acids from CO2.