Production of organics from CO₂ by microbial electrosynthesis (MES) at high temperature

BACKGROUND: Microbial electrosynthesis (MES), a process by which microorganisms reduce carbon dioxide to multi-carbon compounds using electrical current as energy source, has so far been demonstrated at temperatures ranging from 25°C to 37°C. Elevated operating temperatures, however, could improve overall performance and product recovery. Here the effect of temperature on MES by the acetogenic thermophiles Moorella thermoacetica and Moorella thermoautotrophica is investigated. RESULTS: Experiments were performed at operating temperatures ranging from 25°C to 70°C to determine the optimum operating temperature for MES. Optimal performance was observed to be close to the optimum growth temperatures reported for these strains. Production rate and activation energy of acetate at 60°C was 6.9±0.6 mM m^-2 d^-1 and 45.1±3.8 kJ mol^-1 for M. thermoacetica and 11.6±0.9 mM m^-2 d^-1 and 58.9±2.5 kJ mol^-1 for M. thermoautotrophica with columbic efficiencies (CE) of 79±15% and 72±4%, respectively. CONCLUSION: Considering CE and acetate production rate during MES, M. thermoautotrophica outperformed M. thermoacetica over a wide range of operating temperatures. Current-dependent reduction of CO₂ also occurred below the minimum growth temperature of these strains, suggesting that MES is non-growth associated.