Getting to the source

P lenty of strange diets have captured the public imagination over the years, but Harvard scientists have identified what may be the strangest of them all - sunlight and electricity. Led by Peter Girguis, the John L. Loeb Associate Professor of the Natural Sciences, and Arpita Bose, a postdoctoral fellow in organismic and evolutionary biology, a team of researchers has demonstrated that the bacterium Rhodopseudomonas palustris can use natural conductivity to pull electrons from minerals located deep in soil and sediment while remaining at the surface, where it absorbs the sunlight needed to produce energy. The study was described in a Feb. 26 paper in Nature. "When you think about electricity and living organisms, most people default to Mary Shelley's 'Frankenstein,' but we've long understood that all organisms actually use electrons - what constitutes electricity - to do work," Girguis said. "At the heart of this paper is a process called extracellular electron transfer, which involves moving electrons in and out of cells. What we were able to show is that these microbes take up electricity, which goes into their central metabolism, and we were able to describe some of the systems that are involved in that process." In the wild, the microbes rely on iron to provide the electrons they need to produce energy, but tests in the lab suggest the iron itself isn't critical for the process.