The strain of Cellulomonas fimi NBRC 15513 can generate electricity with cellulose as fuel without mediator using a single chamber type microbial fuel cell (MFC) which had 100 mL of chamber and 50 cm(2) of the air cathode. The MFCs were operated over five days and showed the maximum current density of 10.0 +/- 1.8 mA/m(2), the maximum power density of 0.74 +/- 0.07 mW/m(2) and the ohmic resistance of 6.9 k Omega According to the results of cyclic voltammetry, the appearance of the oxidation or reduction peak was not observed from the cell removed solution. The fact is that C. fimi does not secrete mediator-like compounds, while the oxidation peak was observed at + 0.68 V from the phosphate buffer containing the washed cell. The peak appearance was caused by the electron transfer activity of which corresponds to cytochrome c, and disappeared after adding antimycin A which inhibits the electron transfer activity. The cell was alive throughout the experiment as the result of a colony forming unit on Luria-Bertani agar plates. This was thought that cytochrome c was on the membrane surface of the living cell and played a role in the direct electron transfer between the cells and anode. (C) 2019, The Society for Biotechnology, Japan. All rights reserved.