In These Microbes, Iron Works Like Oxygen

A pair of papers from a UW–Madison geoscience lab shed light on a curious group of bacteria that use iron in much the same way that animals use oxygen: to soak up electrons during biochemical reactions. When organisms—whether bacteria or animal—oxidize carbohydrates, electrons must go somewhere.

The studies can shed some light on the perennial question of how life arose, but they also have slightly more practical applications in the search for life in space, said senior author Eric Roden, a professor of geoscience at UW–Madison.
Animals use oxygen and "reduce" it to produce water, but some bacteria use iron that is deficient in electrons, reducing it to a more electron-rich form of the element. Ironically, electron-rich forms of iron can also supply electrons in the opposite "oxidation" reaction, in which the bacteria literally "eat" the iron to get energy.


Iron is the fourth-most abundant element on the planet, and because free oxygen is scarce underwater and underground, bacteria have "thought up," or evolved, a different solution: moving electrons to iron while metabolizing organic matter.

These bacteria "eat organic matter like we do," says Roden. "We pass electrons from organic matter to oxygen. Some of these bacteria use iron oxide as their electron acceptor. On the flip side, some other microbes receive electrons donated by other iron compounds. In both cases, the electron transfer is essential to their energy cycles."