Microbial electrosynthesis (MES) systems can store renewable energy and CO 2 in many-carbon molecules inaccessible to abiotic electrochemistry. Here, we develop a multiphysics model to investigate the fundamental and practical limits of MES enabled by direct electron uptake and we identify organisms in which this biotechnological CO 2 -fixation strategy can be realized. Systematic model comparisons of microbial respiration and carbon fixation strategies revealed that, under aerobic conditions, the CO 2 fixation rate is limited to <6 μmol/cm 2 /hr by O 2 mass transport despite efficient electron utilization. In contrast, anaerobic nitrate respiration enables CO 2 fixation rates >50 μmol/cm 2 /hr for microbes using the reductive tricarboxylic acid cycle. Phylogenetic analysis, validated by recapitulating experimental demonstrations of electroautotrophy, uncovered multiple probable electroautotrophic organisms and a significant number of genetically tractable strains that require heterologous expression of <5 proteins to gain electroautotrophic function. The model and analysis presented here will guide microbial engineering and reactor design for practical MES systems.
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Abel et al. (2020) studied this question.