Magnetite crystals act like rechargeable batteries (Image: Claire Cordier/Getty)

It’s electrifying. Bacteria have been found growing on tiny particles of natural magnets. The bugs are a mixed colony, capable of “eating” and “breathing” electrons from metals.

Electric bacteriahave become a hot topic in recent years, with the discovery that some bugs found beneath seabeds and riverbeds around the world can harvest electrons from tiny metallic particles. By donating electrons to the bacteria, the iron particles effectively become a source of energy to the cells. Other species of bacteria effectively breathe metallic particles, by dumping excess electrons on them.

Now, James Byrne of the University of Tübingen in Germany and his team have found that tiny crystals of magnetite, a common magnetic mineral, can be used as both electron acceptors and electron donors – essentially working as a battery. He grew colonies composed of Geobacter and Rhodopseudomonas bacteria on magnetite and found that Geobacter could dump electrons onto the crystals, while Rhodopseudomonas could harvest electrons from them.


In the wild, Byrne says the two reactions probably happen during day and night cycles, or tide phases, with each type of bacteria active at different points in the cycle. The magnetite crystals, he says, act like natural rechargeable batteries for the colonies: recharged in electrons by Geobacter, and depleted by Rhodopseudomonas.

Lars Peter Nielsen of Aarhus University in Denmark says the discovery is fascinating and completes a picture of magnetite as a mineral with multiple roles in geomicrobiology. It can serve as a conductor, a sink and a source of electrons, depending on the needs of the microbes, he says.

Journal reference: Science, DOI:10.1126/science.aaa4834