Bacteria that derive energy from uranium radiation have been discovered deep underground

Astrobiologists at Indiana University Bloomington have made a remarkable discovery, finding bacteria living 2 miles underground that derive energy from uranium radiation. Research conducted in a South American gold mine sheds new light on the possibility of life in extreme subsurface conditions. These organisms, from the family Firmicutes, may be millions of years old and demonstrate the ability to metabolize hydrogen and sulfate, allowing them to survive in environments lacking sunlight. This discovery could change our understanding of life on other planets.

Researchers from Indiana UniversityAstrobiologists have discovered uranium-mimicking bacteria living 2 miles (3.2 km) beneath Earth's surface. These exotic and resilient organisms suggest that such life could exist in subsurface environments on all sorts of planets previously considered inhospitable.

Details of the discovery were published in the journal Nature by researchers from Indiana University Bloomington and eight collaborating institutions. In a paper that reads like a scene from an "Indiana Jones" script, the researchers describe how they descended into a hot, gas-filled shaft inside a South American gold mine to investigate a new underwater fracture in uncontaminated rock.

Water samples from the fracture were collected over a 54-day period to determine whether the microbial community, if present, had changed structure and character, and whether contamination had occurred. "We know surprisingly little about the origins, development, and constraints of life on Earth," said biogeochemist Lisa Pratt. "Scientists are just beginning to study the diverse organisms that live in the deepest regions of the ocean. The rocky crust of the Earth beneath the surface remains virtually unexplored. The organisms we describe in this paper live in a completely different environment than the one we know on the surface."

Subsurface bacteria are a controversial topic, as many scientists are skeptical of life forms that don't live on the surface, where sunlight reaches. Previously, it was widely believed that underground microbes were more relics heading towards extinction than perpetual survival. However, Pratt and her collaborators are now revealing evidence that bacterial communities are indeed persistent—they can be millions of years old.

DNA analysis revealed that the species inhabiting the fracture region originated from the Firmicutes family. Further analysis suggests that subsurface Firmicutes lost contact with their surface cousins approximately 3 to 25 million years ago. Researchers are unsure how surface Firmicutes managed to colonize the area at such great depths.

Perhaps most fascinating are the feeding habits of the newly discovered organisms. They derive energy not from daylight but from radiation from uranium ores. Radiation emanating from uranium minerals or near the fracture allows the formation of hydrogen from the splitting of water and the formation of sulfate from the splitting of sulfur minerals. Hydrogen is highly energetic when reacted with oxygen or other compounds, such as sulfate, and Firmicutes are able to extract energy from the hydrogen-sulfate reaction, allowing other microbes to feed on the chemical residues.

Firmicutes can be said to function much like photosynthetic organisms—such as plankton and trees—that capture sunlight, which ultimately benefits other organisms. In this subsurface case, Firmicutes bacteria are the producers, as they capture the energy released during hydrogen formation, sustaining microbial communities.