Efficiency estimates for electromicrobial production of branched-chain hydrocarbons

In electromicrobial production (EMP), electricity is used as microbial energy to produce complex molecules starting from simple compounds like CO2. The aviation industry requires sustainable fuel alternatives that can meet demands for high-altitude performance and modern emissions standards. EMP of jet fuel components provides a unique opportunity to generate fuel blends compatible with modern engines producing net-neutral emissions. Branched-chain hydrocarbons modulate the boiling and freezing points of liquid fuels at high altitudes. In this study, we analyze the pathways necessary to generate branched-chain hydrocarbons in vivo utilizing extracellular electron uptake (EEU) and H-2-oxidation for electron delivery, the Calvin cycle for CO2-fixation and the aldehyde deformolating oxygenase decarboxylation pathway. We find the maximum electrical-to-fuel energy conversion efficiencies to be 40:0(+0:6) (- 4:4) % and 39:8(+0:7) (- 4:5)%. For a model blend containing straight-chain, branched-chain, and terpenoid components, increasing the fraction of branched-chain alkanes from zero to 47% only lowers the electrical energy conversion efficiency from 40:1(+0:7) (- 4:5) % to 39:5(+0:7) - (4:6)%.