Scientists have recovered microorganisms from ancient Antarctic ice and coaxed it 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 up to 8 million years.
If warming melts the glaciers, the DNA could fuel a new wave of bacterial evolution, the researchers reported in the Proceedings of the National Academy of Sciences.
The findings also challenge the long-held notion that life couldn’t possibly exist in Antarctic glaciers.
“Five years ago, people would have told you it’s an environment too extreme for life,” said Louisiana State University microbiologist Brent Christner, 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 square that were excavated from the Transantarctic Mountains.
The ice from Mullins Valley was about 100,000 years old, and ice from Beacon Valley was about 8 million years old. The samples were taken from 6 inches beneath the surface of a glacier, which was buried under up to 30 inches of debris.
After the ice was carefully melted to prevent contamination by modern microorganisms, the researchers poured a couple 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 they 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, the researchers spiked the meltwater with nutrients and incubated it at 40 degrees.
The samples from Mullins Valley doubled about once a week, and the older samples 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 ancient microorganisms.
“It stands to reason,” he said. “In the lab, if we want to preserve a sample, we stick it in the freezer.”
Christner has reported finding viable microbes in 500,000-year-old Antarctic ice, but his critics raised concerns that the results were because of contamination by modern organisms.
Christner said he was satisfied that the researchers in the new study took precautions to prevent contamination.
However, he said he wasn’t sure what to make of the relatively high concentrations of microbes found in the glacial meltwater. At 3,280 to 50,000 organisms per milliliter, it was 10 to 100 times greater than the concentration in his own studies.
Bidle’s team said the microbial concentrations were comparable to those of polar freshwater and sea ice.
The microorganisms might grow on their own if they are released from the ice through glacial melting, Bidle said. “We don’t know for sure, but it’s very possible,” he said.
The researchers also collected enough data to measure the rate at which DNA degrades 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 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.
“All of the genetic material would have been obliterated and sterilized,” he said.
However, he said, Mars is close enough to potentially send frozen DNA our way.
Bidle said that if the organisms could survive in Antarctica, they might persist in pockets of Martian ice.
“This particular ice has a strong similarity to data that’s coming back from Mars,” Bidle said. “This is the closest thing we have on this planet.”