April 17, 2009

New Microbes Discovered In Underground Antarctic Pool

Scientists have once again found cause to marvel at the brilliant tenacity of life.

In a small subterranean pool of highly concentrated salt water that hasn't seen the sun for some 1.5 million years, researchers have discovered flourishing colonies of previously unknown species microbes.

The red water of Blood Falls that flows from the base of the Taylor Glacier in Antarctica has intrigued scientists since its discovery more than a century ago. A crew of scientists from Harvard and Dartmouth College were sampling and analyzing the iron-rich outflow when they discovered the new microbes that had apparently been trapped in a reservoir beneath the giant glacier. 

Researchers had previously assumed that conditions in the buried body of water were too harsh for any life forms to survive.

Analysis of the water revealed a salt concentration more than four times higher than that found in the oceans "“ meaning that the water is unable to freeze despite temperatures far below 0 degrees Celsius.

Even more surprising, researchers found that the water was completely devoid of oxygen.

"That was when this got really interesting," said Jill Mikucki, a researcher for the Department of Earth Science at Dartmouth College and lead author of the paper published in Science this month. "It was a real "Ëœeureka' moment!"

Lacking the light required for photosynthesis, as well as oxygen and most other nutrients typically needed for survival, researchers suspect that the organisms have clung to life by adapting to breathe the iron leached out from the bottom of the glacier and by feeding on organic matter that was trapped in the frigid water with them when the pool was initially sealed off by the Taylor Glacier some 1.5 - 2 million years ago.

The first explorers to visit this area of Antarctica believed that the dramatic red color of Blood Falls was due to rust or red algae, said Mikucki.  The new research, however, reveals that it is likely due to the iron which the bacteria release from the glacial bedrock while breathing.

Genetic analysis of the bacteria's DNA suggests that despite their extreme isolation, the microbes are most likely descendents of a marine rather than terrestrial bacterial lineage.  Researchers believe that the bacteria's ancestors were likely ocean-dwelling organisms that found themselves trapped in the pool by the rising Antarctic valleys millions of years ago.

"It's a bit like finding a forest that nobody has seen for 1.5 million years," explained Ann Pearson, the Thomas D. Cabot Professor of Earth and Planetary Sciences at Harvard. 

"Intriguingly, the species living there are similar to contemporary organisms, and yet quite different "“ a result, no doubt, of having lived in such an inhospitable environment for so long."

"This briny pond is a unique sort of time capsule from a period in Earth's history," added Mikucki.  "I don't know of any other environment quite like this on Earth."

Because of the thickness of the ice sheet covering it, researchers have been unable to drill to the hidden pool to measure its exact dimensions. However, they believe it to be buried beneath about 400 meters of ice at a distance of approximately four kilometers away from where it flows out at Blood falls.

The team believes that their work has helped to answer some of the questions about how life persists in inhospitable environments, even while raising new ones.

"Among the big questions are "Ëœhow does an ecosystem function below glaciers?', "ËœHow are they able to persist below hundreds of meters of ice and live in permanently cold and dark conditions for extended periods of time "“ in the case of Blood Falls, over millions years?'," said Mikucki.

The Taylor Glacier reservoir may also serve as a sort of living laboratory in the future, allowing scientists to examine how life forms may have evolved and survived during the hypothesized "Snowball Earth" period, when some scientists suggest that global temperatures may have been on par with those of modern day Antarctica.  It might also give researchers a chance to explore the plausibility of life on other icy planets, like the Martian ice caps or Jupiter's frozen moon, Europa.


Image 1: Blood Falls at the snout of the Taylor Glacier overlooking Lake Bonney. Credit: Peter West / NSF

Image 2: A cross-section of Blood Falls showing how micorbial communities survive. Credit: Zina Deretsky / NSF


On the Net: