Scientists descending more than 2 miles into the hot, fractured rocks of a South African gold mine have discovered clans of microbes that have thrived there in total isolation for millions of years. Their quest, the scientists say, reveals more clearly than ever how life can exist in the most extreme environments imaginable: beneath the surface of Mars, perhaps, or on almost any other planet in the galaxy. The ancient bacteria exist in an environment that scientists describe as by far the most outlandish for any organisms ever found -- they are long removed from life-giving sunlight and living only on sulfate minerals and hydrogen split from water by uranium's radioactivity. Teams of other researchers have long found "extremophile" microbes in the boiling geysers of Yellowstone National Park, on erupting volcanoes in rifts on the ocean floor, in the high desert of the Andes, in acidic springs and polar ice caps -- but the bacteria beat them all for their extreme lifestyle. The organisms were discovered and identified by a broad group of researchers reporting today in the journal Science. The researchers include geologists from Princeton, Taiwan and Indiana; geneticists at Berkeley and Walnut Creek; and others in Nevada, Canada and Germany. The microbes, found by the geologists during nearly 10 years of exploration, are among a large class of well-known surface bacteria called Firmicutes. Scientists at the Joint Genome Institute in Walnut Creek recently sequenced the genes of many in the community of microbes found in the cave, including one wormlike bacterium they have identified as the newly named Desulforudis audaxviator. "These bugs come from a formation at least 3 million and probably tens of millions of years old," said biologist Terry Hazen, head of the Lawrence Berkeley National Laboratory's ecology department and a co-author of the report. "They're living happily down there, remote and secluded, and they have the ability to adapt to anything that comes their way." Geologist Lisa Pratt of Indiana University, also a co-author, said the bacteria show that life is far more adaptable than scientists imagined. "Their community has evolved in an environment that's a wake-up call, telling us that if it can happen on Earth, it can surely happen on planets like Mars and maybe on other planets in the universe," she said. Pratt was on the team that explored the depths of the Mponeng gold mine in South Africa's Witwatersrand Basin some 60 miles west of Johannesburg. The mine is the deepest on the African continent, and temperatures at the bottom reach more than 148 degrees. It is heavily stressed, and its fractured rocks are filled with ancient water that is alive with microbes. Li-Hung Lin, now at the National Taiwan University, is the report's lead author, and he too was on the exploration team as a Princeton graduate student working under geologist Tullis Onstott, who has been seeking life in deep mine shafts with Pratt for more than a decade.
Onstott and Pratt said in the report that the volcanic formation where the mine shaft penetrates deeply is nearly 3 billion years old. The water in which the community of microbes lives in rock fractures at the bottom of the shaft, they reported, has been isolated from the Earth's surface for millions of years. The dates are based on analyzing the ratio of noble gases like neon, krypton and argon who the water. That isolated water, they determined, must have been carried into the rocks all those millions of years ago by meteorites long before volcanic and other tectonic forces turned that part of the Earth's surface upside down. David Des Marais, a geochemist with NASA's Astrobiology Institute at the Ames Research Center in Mountain View, who is not part of the research team, was excited by the report. "This is a very relevant study for Mars," he said. "They've brought a remarkable array of tools to show that these critters lated from the surface for many millions of years. It's really an isolated biosphere down there, and the evidence that the organisms are living only on the chemicals in the rocks and water is very impressive." While those bacteria love the heat down there, other extremophile hunters have discovered classes of microbes on the Earth's surface that must love extreme cold. In a report published Thursday on the International Journal of Astrobiology Web site, astronomers at the Space Telescope Science Institute and microbiologists the University of Maryland said they have analyzed a group of microorganisms that have evolved to survive and reproduce in briny ice at temperatures well below the freezing point of water. "The lowest temperatures at which these organisms can thrive fall within the temperature range on present-day Mars," said Neill Reid, an astronomer at the telescope institute who led the research team. "The low temperature limit for life is particularly important since, both in the solar system and the Milky Way galaxy, cold environments are much more common than hot environments."