Metabolism, the collection of biochemical reactions that convert nutrients into energy, comes with a catch: It leaves behind a bevy of unneeded electrons, which the cell must somehow rid itself of. That, in essence, is why we breathe—the oxygen molecules we inhale get absorbed in the bloodstream and taken up by our cells to act as terminal electron acceptors in the metabolic process, ultimately emerging in the form of water.
But some harsh environments don’t afford the luxury of soluble, ingestible electron acceptors. For those cases, microbes such as the marine bacterium Shewanella oneidensis have evolved a unique contingency plan: If the acceptor can’t get to the electrons, they send the electrons to the acceptor. Shewanella, for instance, can export electrons to extracellular minerals such as iron, manganese, and uranium oxides and produce a current that researchers are now learning to harness in microbial fuel cells and other...
