A Redox-Enzyme Integrated Microbial Fuel Cell Design Using the Surface Display System in <i>Shewanella oneidensis</i> MR-1

A biofuel cell is an electrochemical device using exoelectrogen or biocatalysts to transfer electrons from redox reactions to the electrodes. While wild-type microbes and natural enzymes are often employed as exoelectrogen and biocatalysts, genetically engineered or modified organisms have been developed to enhance exoelectrogen activity. Here, we demonstrated a redox-enzyme integrated microbial fuel cell (REI-MFC) design based on an exoelectrogen-enhancing strategy that reinforces the electrogenic activity of <i>Shewanella oneidensis</i> MR1 by displaying an extra redox enzyme on the cell surface. We constructed the cell-surface display system for <i>Shewanella oneidensis</i> MR-1 by porting the autotransporter of <i>Escherichia coli</i> into the MR-1 strain. The functionality of the display system was validated by examining the various enzymes displayed on the cell surface of <i>S. oneidensis</i> MR-1. The implementation of the REI-MFC design was accomplished by an engineered MR-1 strain displaying a redox enzyme originating from swine NADH-cytochrome b5 reductase 3 (B5R3). At the polarization test of enhanced exoelectrogen in an operating MFC environment, the current generation (Δ<i>I</i>_a, peak: 10.4 ± 1.9 μA) of the MR-1 displaying B5R3 was 4.7-fold higher than that of wild-type MR-1 (2.2 ± 0.3 μA). The maximum charge transfer resistance (<i>R</i>_ct) under the optimized electrochemical test conditions was 70% lower than the wild-type MR-1. The cell surface display system for <i>S. oneidensis</i> MR-1 exploited in this study facilitated the exoelectrogen activity in the REI-MFC design.