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Scientists revive life frozen in polar ice

TUESDAY, AUG. 7, 2007

Scientists have recovered microorganisms from ancient Antarctic ice and coaxed them back to life in the lab, according to a study published today.

The glacial ice acted as a “gene popsicle,” preserving DNA that hasn’t circulated in the gene pool for as long as 8 million years.

If warming temperatures cause the glaciers to melt, the DNA could fuel a wave of bacterial evolution, the researchers reported in the Proceedings of the National Academies of Science.

The findings also challenge the long-held notion that life couldn’t exist in the frozen climes of Antarctic glaciers.

“Five years ago, people would have told you it’s an environment too extreme for life,” said Brent Christner, a Louisiana State University microbiologist who wasn’t involved in the study. “Now that view is changing.”

Marine microbiologist Kay Bidle, the study’s lead author, and his colleagues studied blocks of ice about 8 inches on each side excavated from the Transantarctic Mountains.

The ice from Mullins Valley was about 100,000 years old, and ice from Beacon Valley about 8 million years old. The samples were taken from 6 inches beneath the surface of a glacier, which itself was buried under up to 30 inches of debris.

After the ice carefully was melted to prevent contamination by modern microorganisms, the researchers poured a couple of ounces of the water into sterile glass flasks and added compounds to test the metabolic activity of the ancient creatures. The organisms incorporated sugars into their cells and turned amino acids into proteins, said Bidle, a member of the Institute of Marine and Coastal Sciences at Rutgers University in New Brunswick, N.J.

To see whether the organisms would grow, researchers spiked the meltwater with nutrients and incubated it at 40 degrees Fahrenheit.

Samples from Mullins Valley doubled about once a week, and the older sample from Beacon Valley doubled in 30 to 70 days, according to the study. The older specimens probably took longer to divide because their DNA was more severely degraded, Bidle said.

Christner said he wasn’t surprised that the team was able to rehabilitate the microorganisms.

“It stands to reason,” he said. “In the lab, if we want to preserve a sample, we stick it in the freezer.”

The microorganisms might grow on their own if released from the ice through glacial melting, Bidle said. “We don’t know for sure, but it’s very possible,” he said.

Researchers also collected enough data to measure the rate at which DNA degrades over time and calculated that it has a half-life of 1.1 million years. The primary culprit, they said, was cosmic radiation, to which Antarctica is especially vulnerable.

Some scientists have speculated that microorganisms – or at least smatterings of genes – could have traveled to Earth from interstellar space frozen in the icy heads of comets. But based on the lifespan of DNA, there is no chance that viable genetic material has reached us from beyond the solar system, Bidle said.

But, he said, Mars is close enough potentially to send frozen DNA our way. Bidle said that if the organisms can survive in Antarctica, they might persist in pockets of Martian ice.


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