Electricity-enhanced anaerobic, non-photosynthetic mixotrophy by Clostridium carboxidivorans with increased carbon efficiency and alcohol production.

[Display omitted] • Electricity-enhanced ANP mixotrophy was investigated for the first time. • Electricity-enhanced mixotrophy with MV or biochar showed carbon efficiency of >80%. • Alcohol/acid ratio of 0.402 mol/mol was achieved with MV and electricity. • The carbon efficiency obtained was the highest reported in C. carboxidivorans. Anaerobic, non-photosynthetic mixotrophy (ANP mixotrophy) is a process whereby glucose consumption and CO 2 fixation via the Wood-Ljungdahl pathway occur concurrently. ANP mixotrophy supplemented with exogenous reducing power and CO 2 shows the potential of reducing the carbon loss from glycolysis and enhancing the production of biofuels. Previous studies used H 2 and syngas as the exogenous source of reducing power, however, the low solubility of H 2 and CO impeded their efficient utilization by bacteria. This study used a bio-electrochemical system (BES) to supply electrons to fix CO 2 and shift the metabolite profiles towards more-reduced products in acetogenic bacteria Clostridium carboxidivorans. C. carboxidivorans showed no electroactivity, but the electricity-enhanced fermentation without electron mediator showed higher alcohol production and carbon efficiency compared to open-circuit fermentation. C. carboxidivorans could fix CO 2 autotrophically with the electrical current and electron mediator MV or biochar. Electricity-enhanced mixotrophy with MV showed a higher alcohol/acid ratio and carbon efficiency in liquid products (0.402 mol/mol and 82.8%, respectively) compared to those without MV and electricity (0.067 mol/mol and 52.2%, respectively). The addition of biochar in electricity-enhanced mixotrophy increased the carbon efficiency to 80.3%, and promoted the synthesis of butyrate and hexanoate. This study investigated the electricity-enhanced ANP mixotrophic fermentation for the first time, and demonstrated its potential for enhancing carbon efficiency and alcohol production with C. carboxidivorans. [ABSTRACT FROM AUTHOR]