New Take on Dietary Habits of Ancient Life

Hungry microorganisms in the primordial world may have relied on a scarcely explored process called sulfur disproportionation to stay well-fed (Science 2007, 317, 1534). Microbe menus can be pieced together to as far back as 2.7 billion years ago, but there's a dearth of earlier dining data. Some researchers have found evidence that ancient bacteria and archaea used sulfate reduction to sulfide as an energy source. Now, Pascal Philippot, a geochemist at the Institute of Earth Physics, in Paris, and international colleagues report that microorganisms from 3.5 billion years ago preferred elemental sulfur instead of sulfate. Employing sophisticated sulfur isotope analysis, the researchers conclude that microbes from remote Australia got their energy by enzymatically disproportionating sulfur—simultaneously reducing and oxidizing it—to hydrogen sulfide and sulfate. In a Science commentary, biogeochemist Bo Thamdrup of the University of Southern Denmark says the work provides a new piece for a microbial metabolism puzzle in which "most pieces are missing."