BACKGROUND The c-type cytochrome of the CymA of Shewanella oneidensis MR-1 is essential for the anaerobic respiration of Shewanella sp. and transfers electrons from the inner membrane to various terminal electron acceptors, such as soluble redox shuttles and insoluble metal oxides. CymA is believed to be a passage to the outer membrane for dissipating the respiratory electron to the carbon electrode in a microbial fuel cell (MFC) with simultaneous electricity generation. While the deletion and heterologous expression of cymA in Escherichia coli have been studied, there are no reports of the overexpression and its effects on the corresponding bioelectrochemical performance in a MFC. RESULTS The cymA gene was overexpressed in Shewanella oneidensis MR-1, and its upregulation was examined under aerobic, anaerobic, and MFC operating conditions by a reverse transcription-polymerase chain reaction (RT-PCR). Overexpression of the CymA protein was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The MFCs inoculated with the engineered strains of MR-1 achieved a higher maximum power of 0.13 mW and specific growth rate of 0.087 h(-1) than those of the wild type MR-1 (0.11 mW and 0.043 h(-1), respectively). The higher electrochemical activity of the mutant strains demonstrated by cyclic voltammetry and linear sweep voltammetry, indicates that more respiratory electrons can be transferred to the electrodes through overexpression of the cymA gene of MR-1 in a MFC. CONCLUSION Overexpression of CymA improves the bioelectrochemical performance of MFCs. This suggests that metabolic engineering of a membrane-associated redox protein, such as CymA, can further improve electricity generation of MFCs and produce an electrochemically enhanced bioprocess. (c) 2018 Society of Chemical Industry