The project MTRoute investigated the molecular mechanisms of extracellular electron transfer (EET) mediated by the porin–cytochrome complex MtrCAB from different Shewanella species, as well as from more phylogenetically distant organisms such as Aeromonas hydrophila and Vibrio natriegens. This complex is composed of the decaheme cytochromes MtrA and MtrC, and the porin protein MtrB where MtrA is embedded (Figure). These complexes span the outer membrane of specialized microorganisms known as electroactive microbes and enable electrons to move from the cell interior to external acceptors such as minerals or electrodes. Understanding how these proteins facilitate electron transport is crucial for advancing bioelectrochemical systems (BES), a promising technology that harnesses electroactive microbes to transfer electrons produced by the oxidation of organic matter in wastewater to electrodes, thereby generating electricity. This particular BES system is generally called a Microbial Fuel Cell (MFC). However, the performance of BES is currently limited by incomplete knowledge of the structural and mechanistic factors that control and enhance microbial electron transfer at the cell–electrode interface.
The overall objective of MTRoute was to elucidate the structural and functional diversity of MtrCAB complexes and identify the molecular mechanisms that control electron transfer at the bacterial cell surface. Through an integrated approach combining molecular biology, structural biophysics (NMR spectroscopy, X-ray crystallography and analytical ultracentrifugation (AUC)), (bio)electrochemical analyses, and computational modelling, the project was crucial to:
1. Characterize the functional diversity of MtrCAB complexes from different electroactive bacteria;
2. Identify the molecular factors that define electron transfer rates;
3. Engineer the model electroactive microbe Shewanella oneidensis with enhanced electron transfer capabilities for improved BES performance.
MTRoute aims to generate new insights into the mechanistic basis of EET and to identify structural features that can be harnessed to rationally design high-performance electroactive microbes. These advances have the potential to accelerate the development of sustainable energy technologies to generate renewable electricity from wastewater. By enabling more efficient BES, the project directly supports the objectives of the European Green Deal and REPowerEU, which aim to reduce dependence on fossil fuels, expand renewable energy production, and drive the transition to a climate-neutral European economy.
