For mouthless, lungless bacteria, breathing is a bit more complicated than it is for humans.

We inhale oxygen and exhale carbon dioxide; Geobacter — a ubiquitous, groundwater-dwelling genus of bacteria — swallow up organic waste and ‘exhale’ electrons, generating a tiny electric current in the process.

Those waste electrons always need somewhere to go (usually into a plentiful underground mineral like iron oxide), and Geobacter have an unconventional tool to make sure they get there.