Bacteria work together to survive Earth’s depths

Abstract

Thousands of feet below the Earth’s surface seems an unlikely cradle for life. Indeed, for a long time, scientists wondered if any life could survive in such a hostile, pitch black, oxygen-poor environment. Working in the depths of a gold mine, Maggie Lau ( Left ) and Rachel L. Harris ( Right ) filter water to capture microbial cells onto a filter membrane. Image courtesy of Rachel L. Harris (Princeton University, Princeton). But about two decades ago, researchers found the first substantive evidence of organisms living deep underground. A Department of Energy drilling project had recovered rocks from more than a mile below the Earth’s surface in the Taylorsville Basin in Virginia, and scientists were surprised to find that these rocks harbored bacteria. More recently, researchers went looking for microscopic worms in deep mines, and discovered a variety of eukaryotic organisms living at these depths (1, 2). Most of these eukaryotes survive by eating deep-living bacteria. But there’s still a lot we don’t know about how the bacteria themselves survive in an environment without sunlight or plentiful oxygen for energy. Recent work, based on samples painstakingly retrieved from deep gold mines, appears to provide a crucial clue: the bacteria work together in intricate networks, cooperating to survive. “We have long understood that life exists in the deep subsurface, but we don’t actually know what they’re doing in that environment,” says Maggie Lau, a geomicrobiologist at Princeton University and the study’s first author. Lau and her colleagues identified and analyzed the metabolic networks used by deep-living bacterial communities. By capturing the “metabolic landscape” of these underground environments, the authors showed that the bacteria use a wider range of energy sources than expected, and work together to survive (3). Studying these kinds of metabolic landscapes will be crucial for understanding …