Bacteria derive all energy needs from radioactivity
A Princeton University-led research group has discovered an isolated community of bacteria nearly two miles underground that derives all of its energy from the decay of radioactive rocks rather than from sunlight. According to members of the team, the findings suggest life might exist in similarly extreme conditions, even on other worlds.
The self-sustaining bacterial community, which thrives in nutrient-rich groundwater found near a South African gold mine, has been isolated from the Earth’s surface for several million years. It represents the first group of microbes known to depend exclusively on geologically produced hydrogen and sulfur compounds for nourishment.
The extreme conditions under which the bacteria live bear a resemblance to those of early Earth, officials said, potentially offering insights into the nature of organisms that lived long before Earth had an oxygen atmosphere.
The scientists, who come from nine collaborating institutions, had to burrow 2.8 kilometers beneath Earth’s surface to find these unusual microbes, leading the scientists to their speculation that life could exist in similar circumstances elsewhere in the solar system.
"What really gets my juices flowing is the possibility of life below the surface of Mars," said Tullis Onstott, a Princeton University professor of geosciences and leader of the research team. "These bacteria have been cut off from the surface of the Earth for many millions of years, but have thrived in conditions most organisms would consider to be inhospitable to life. Could these bacterial communities sustain themselves no matter what happened on the surface? If so, it raises the possibility that organisms could survive even on planets whose surfaces have long since become lifeless."
Professor Onstott’s team published its results in the Oct. 20 issue of the journal Science.
Because the groundwater the team sampled to find the bacteria comes from several different sources, it remains difficult to determine specifically how long the bacteria have been isolated. The team estimates the time frame to be somewhere between 3 million and 25 million years, implying that living things are even more adaptable than once thought.
"We know surprisingly little about the origin, evolution and limits for life on Earth," said biogeochemist Lisa Pratt, who led Indiana University’s contribution to the project. "Scientists are just beginning to study the diverse organisms living in the deepest parts of the ocean, and the rocky crust on Earth is virtually unexplored at depths more than half a kilometer below the surface. The organisms we describe in this paper live in a completely different world than the one we know at the surface."
The subterranean world, Professor Onstott said, is a pool of hot, pressurized salt water that stinks of sulfur and noxious gases humans would find unbreathable. But the newly discovered bacteria, which are distantly related to the Firmicutes division of microbes that exist near undersea hydrothermal vents, flourish there.
"The radiation allows for the production of lots of sulfur compounds that these bacteria can use as a high-energy source of food," Professor Onstott said. "For them, it’s like eating potato chips."

