Electromicrobiology
Bacteria that conduct electricity over centimetres, exchange electrons with minerals, and signal with ion waves.
Overview reviewed
Where things stand
Microbes were long known to transfer electrons to minerals and electrodes; Geobacter and Shewanella are classic examples. Two discoveries turned this into its own field. Cable bacteria, reported in 2012, are filamentous bacteria that conduct electrons over centimetre distances through seafloor sediment, linking sulfide oxidation deep in the mud to oxygen at the surface (Pfeffer et al., Nature, 2012). Separately, bacterial biofilms were shown to coordinate growth with potassium-ion waves moving through ion channels, a form of electrical signalling similar to that in neurons (Prindle et al., Nature, 2015).
What is contested
The structure of Geobacter "nanowires" has been debated: early work described conductive pili, and later cryo-EM studies identified chains of cytochrome proteins. The two views are now being reconciled. The exact conduction mechanism in cable bacteria fibres, including the role of a nickel-containing cofactor, is still being worked out.
Applications
Microbial fuel cells, electrode-based bioremediation, and conductive protein materials are active areas, but most are not yet competitive outside the lab.
What to watch
Pure cultures of cable bacteria, atomic structures of their conductive fibres, and engineered "living electronics".
Milestones
- 2005Microbial nanowires. Derek Lovley's group reports that *Geobacter* bacteria use conductive protein filaments to pass electrons to iron minerals outside the cell, starting the study of microbial nanowires.
- 2012Cable bacteria discovered. Filamentous bacteria are found to conduct electrons over centimetre distances through marine sediment, linking chemical reactions that happen far apart. They become a model system for biological conduction.
- 2015Bacteria signal with ion waves. Bacterial biofilms are shown to coordinate metabolism with waves of potassium ions released through ion channels, a form of electrical signalling similar to that in neurons.
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