Electron Transfer Beyond the Outer Membrane: Putting Electrons to Rest

Extracellular electron transfer (EET) is the physiological process that enables the reduction or oxidation of molecules and minerals beyond the surface of a microbial cell. The first bacteria characterized with this capability were Shewanella and Geobacter, both reported to couple their growth to the reduction of iron or manganese oxide minerals located extracellularly. A key difference between EET and nearly every other respiratory activity on Earth is the need to transfer electrons beyond the cell membrane. The past decade has resolved how well-conserved strategies conduct electrons from the inner membrane to the outer surface. However, recent data suggest a much wider and less well understood collection of mechanisms enabling electron transfer to distant acceptors. This review reflects the current state of knowledge from Shewanella and Geobacter, specifically focusing on transfer across the outer membrane and beyond-an activity that enables reduction of highly variable minerals, electrodes, and even other organisms.

Automated summary

Extracellular electron transfer is a physiological process in which microbial cells are able to transfer electrons beyond their cell membrane, enabling reduction or oxidation of molecules and minerals. Shewanella and Geobacter were the first bacteria known to possess this capability, utilizing it to couple their growth to the reduction of extracellular iron or manganese minerals. While the transfer of electrons from the inner membrane to the outer surface has been well-studied, recent data suggests a wider range of mechanisms that enable electron transfer to distant acceptors.