miércoles, 6 de febrero de 2013

Bacteria Found Deep Under Antarctic Ice, Scientists Say

Published: February 6, 2013

For the first time, scientists report, they have found bacteria living in the cold and dark deep under the Antarctic ice, a discovery that might advance knowledge of how life could survive on other planets or moons and that offers the first glimpse of a vast ecosystem of microscopic life in underground lakes in Antarctica.

Dr. Alberto Behar, JPL/ASU; underwater camera funded by NSF and NASA. The first view of the bottom of subglacial Lake Whillans in Antarctica.

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A network of hundreds of lakes lies sandwiched between the continent’s land and the ice that covers it, and scientists had thought that it could harbor life. The discovery is the first confirmation.

It transforms the way we view the Antarctic continent,” said John Priscu of Montana State University, a leader of the scientific expedition.

After drilling through a half-mile of ice into the 23-square-mile, 5-foot-deep Lake Whillans, the expedition scientists recovered water and sediment samples that showed clear signs of life, Dr. Priscu said, speaking from McMurdo Station in Antarctica on Tuesday. They saw cells under a microscope, and chemical tests showed that the cells were alive and metabolizing energy.

Dr. Priscu said that every precaution had been taken to prevent contamination of the lake with bacteria from the surface or the overlying ice. In addition, he said, the concentrations of life were higher in the lake than in the borehole, and there were signs of life in the lake bottom’s sediment, which would be sealed off from contamination.

Much more study, including DNA analysis, is needed to determine what kind of bacteria have been found and how they live, Dr. Priscu said. There is no sunlight, so the bacteria must depend on organic material that has drifted into the lake from other sources — for instance, decaying microbes from melting glaciers — or on minerals in the rock of the Antarctic continent.

Chris McKay, a NASA senior scientist, said in an e-mail that such analysis could determine if the bacteria in Lake Whillans have implications for the possible discovery of extraterrestrial life. “If it was using a local energy source, it would be interesting," he said. "If it's just consuming organics carried in from elsewhere, it is of much less interest.” The reason, he said, is that elsewhere in the solar system where there is good evidence of liquid water under thick ice sheets, life would have to depend on minerals alone. "There is not going to be oxygen on other worlds,” Mr. McKay said.

Slawek Tulaczyk of the University of California, Santa Cruz, another leader of the science expedition, said that samples were drawn from as deep as four feet in the sediment, and that oxygen decreased with the depth of the sample.

The scientific project, called Wissard, for Whillans Ice Stream Subglacial Access Research Drilling, was years in the planning and is one of three efforts to investigate the lakes that lie under the Antarctic ice.

A year ago, a Russian expedition penetrated the surface of Lake Vostok, under two miles of ice. They found hints of life on samples from the drill bit, but contamination from the kerosene drilling fluid was a possibility. This year they recovered samples of frozen lake water that are yet to be analyzed.

A British effort to reach Lake Ellsworth, under a mile of ice, was called off in December because of equipment problems.

The American effort, supported by $10 million from the National Science Foundation and other grants, focused on Lake Whillans, which is quite different from the other two lakes. It lies under a half-mile of ice, less than the others, and its water is replenished in about a decade, scientists believe, with meltwater from overlying ice. Lake Vostok is much more sealed off from the surface and is thought to take 10,000 years for its waters to renew. Lake Ellsworth may turn over in about 700 years.

Although Lake Whillans may be more reachable than the other two, doing anything in Antarctica is enormously difficult. It took a tractor convoy 12 days to take the drill and other equipment more than 500 miles over the Ross Ice Shelf to the drilling site from the American research station at McMurdo.

The scientists had four days to collect samples and obtain images of the lake. Several lines of evidence convinced them that they had found microbial life in the lake. First, they saw cells under the microscope and confirmed that DNA was present.

Then they measured evidence of an enzyme that is important in metabolism and a chemical called ATP, for adenosine triphosphate. Molecules of ATP are essentially packets of energy, and their presence was a further indication that the bacteria were living. Further, they found that concentrations of ATP were higher in the lake water than in the water in the borehole, which, Dr. Priscu said, meant that there was more life in the lake and argued against any contamination.

Much further study will be done before scientific results are published and other scientists can look at all the data. Dr. Priscu said that new tests were being done each day, but that DNA tests would have to wait until the scientists returned to the United States.

Our stateside DNA sequence work will tell us who they are,” he said of the microbes, “and, together with other experiments, tell us how they make a living.

But he said he was confident that the researchers had achieved the first glimpse of an ecosystem that had been completely unknown. “It’s the world’s largest wetland,” Dr. Priscu said.

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