A\nRedox-Enzyme Integrated Microbial Fuel Cell Design\nUsing the Surface Display System in <i>Shewanella oneidensis</i> MR‑1

A biofuel\ncell is an electrochemical device using exoelectrogen\nor biocatalysts to transfer electrons from redox reactions to the\nelectrodes. While wild-type microbes and natural enzymes are often\nemployed as exoelectrogen and biocatalysts, genetically engineered\nor modified organisms have been developed to enhance exoelectrogen\nactivity. Here, we demonstrated a redox-enzyme integrated microbial\nfuel cell (REI-MFC) design based on an exoelectrogen-enhancing strategy\nthat reinforces the electrogenic activity of Shewanella\noneidensis MR1 by displaying an extra redox enzyme\non the cell surface. We constructed the cell-surface display system\nfor Shewanella oneidensis MR-1 by porting\nthe autotransporter of Escherichia coli into the MR-1 strain. The functionality of the display system was\nvalidated by examining the various enzymes displayed on the cell surface\nof S. oneidensis MR-1. The implementation\nof the REI-MFC design was accomplished by an engineered MR-1 strain\ndisplaying a redox enzyme originating from swine NADH-cytochrome b5\nreductase 3 (B5R3). At the polarization test of enhanced exoelectrogen\nin an operating MFC environment, the current generation (Δ<i>I</i><sub>a</sub>, peak: 10.4 ± 1.9 μA) of the MR-1\ndisplaying B5R3 was 4.7-fold higher than that of wild-type MR-1 (2.2\n± 0.3 μA). The maximum charge transfer resistance (<i>R</i><sub>ct</sub>) under the optimized electrochemical test\nconditions was 70% lower than the wild-type MR-1. The cell surface\ndisplay system for S. oneidensis MR-1\nexploited in this study facilitated the exoelectrogen activity in\nthe REI-MFC design.