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3 December 2012

Ancient microbes survive beneath the icy surface of Antarctic lake

Researchers have described a viable community of bacteria that ekes out a living in a dark, salty and subfreezing environment beneath nearly 20 metres of ice in one of Antarctica’s most isolated lakes.

The finding could have implications for the discovery of life in other extreme environments, including elsewhere in the solar system.

If, as the researchers postulate, the bacteria survive purely from chemical reactions, as opposed to drawing energy from the sun or other sources, “this gives us an entirely new framework for thinking of how life can be supported in cryo-ecosystems on Earth and in other icy worlds of the universe,” said Alison Murray of Nevada’s Desert Research Institute (DRI), the lead author on the paper, published this week in the Proceedings of the National Academy of Sciences U.S.A..

Lake Vida is the largest of several unique lakes found in the McMurdo Dry Valleys, an ice-free area of the continent.

Lake Vida contains no oxygen, is mostly frozen and possesses the highest nitrous-oxide levels of any natural body of water on Earth. A briny liquid that is approximately six times saltier than seawater percolates throughout the icy environment below a depth of 16 metres with an average temperature of minus 13.4 degrees Celsius (or 8 degrees Fahrenheit).

“This study provides a window into one of the most unusual ecosystems on Earth,” said Murray. “Our knowledge of geochemical and microbial processes in lightless icy environments, especially at subzero temperatures, has been very limited up until now. This work expands our understanding of the types of life that can survive in these isolated, cryo-ecosystems and how different strategies may be used to exist in such challenging environments.”

Murray is a molecular microbial ecologist. She has been a polar researcher for the past 17 years and has participated in 14 expeditions to the Southern Ocean and Antarctic continent.

Despite the very cold, dark and isolated nature of the habitat, the researchers report that the brine harbours a surprisingly diverse and abundant assemblage of bacteria that survive, unlike most life on the planet, without drawing energy, either directly or indirectly, from the sun. Previous studies of Lake Vida dating back to 1996 indicate that the brine has been isolated from outside influences for more than 3,000 years.

Murray and her co-authors and collaborators – including the project’s principal investigator, Peter Doran, of the University of Illinois at Chicago – developed stringent protocols and specialized equipment for their 2005 and 2010 field campaigns that allowed them to sample the lake’s brine while avoiding contaminating the pristine ecosystem.

To sample the unique environment, researchers worked in a secure, sterile tent on the lake’s surface to keep the site and equipment clean as they drilled ice cores, collected samples of the salty brine residing in the lake ice. With these samples they assessed the chemical qualities of the water and its potential for harbouring and sustaining life, and described the diversity of the organisms detected.

Geochemical analyses suggest that chemical reactions between the brine and the underlying iron-rich sediments generate nitrous oxide and molecular hydrogen. The latter, in part, may provide the energy needed to support the brine’s diverse microbial life.

“It’s plausible that a life-supporting energy source exists solely from the chemical reaction between anoxic salt water and the rock,” explained Fritsen, a systems microbial ecologist and research professor in DRI’s Division of Earth and Ecosystem Sciences.

Murray added that further research is currently underway to analyse the abiotic, chemical interactions between the Lake Vida brine and the sediment, in addition to investigating the microbial community by using genomic sequencing approaches. The results could help explain the potential for life in other salty, cryogenic environments beyond Earth.

The Lake Vida brine also represents a cryo-ecosystem that is a suitable and accessible analogue for the soils, sediments, wetlands, and lakes underlying the Antarctic ice sheet that other polar researchers are just now beginning to explore.



 
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