Recently, microbial electrosynthesis (MESs) has been highlighted for the purpose of biological CO2 reduction with simultaneous production of intermediates and value-added chemicals. The bioelectrochemical system (BES), which employs microorganisms and a bacterial community as a biocatalyst, has been developed to convert CO2, a greenhouse gas, into liquid biofuels, such as ethanol and butanol, as well as platform chemicals . Several bacterial species, called cathodophilic microorganisms (e.g., Sporomusa ovata and Clostridium ljungdahlii) were reported to interact with a carbon electrode by accepting electrons supplied externally from a power supply [2-4]. Through this process, oxidized chemical molecules, such as CO2, can be converted to more reduced products, such as acetate and ethanol [4,5]. Since the first report of MESs with S. ovata [3,4], performance has been improved by efforts to optimize the reactor design, regulate the applied potential, and improve the bacterial enrichment method [6-8]. On the other hand, the interaction between microorganism and carbon materials is still unknown, which is the main factor limiting further improvement of the performance of the MES process. For example, insufficient information about microbe-carbon interactions is delaying the advance of the process significantly when the input potential is <−410 mV vs standard hydrogen electrode (SHE), which is the theoretical minimum potential for hydrogen production .