Bacteria thrive without external energy input
By Summit Voice
FRISCO — An ongoing search for isolated life forms in Antartica is yielding results and shedding new light how organisms on Earth can survive in hostile conditions, according to researchers with the University of Illinois at Chicago and Nevada’s Desert Research Institute.
The scientists drilled out cores of ice covering a briny Antarctic lake, finding abundant and diverse metabolically active bacteria in an environment that has been isolated from the surface environment — and external sources of energy — for at least 2,800 years, according to two of the report’s authors, Peter Doran and Fabien Kenig.
Lake Vida, the largest of several unique lakes found in the McMurdo Dry Valleys, contains no oxygen, is mostly frozen and possesses the highest nitrous oxide levels of any natural water body on Earth. A briny liquid that is approximately six times saltier than seawater percolates throughout the icy environment that has an average temperature of minus 13.5 degrees centigrade (or 8 degrees Fahrenheit).
“This provides us with new boundary conditions on the limits for life,” said Doran. “The low temperature or high salinity on their own are limiting, but combined with an absence of solar energy or any new inputs from the atmosphere, they make this a very tough place to make a living.”
“This study provides a window into one of the most unique ecosystems on Earth,” said Dr. Alison Murray, of Nevada’s Desert Research Institute, the report’s lead author. Murray is a molecular microbial ecologist and polar researcher who has participated in 14 expeditions to the Southern Ocean and Antarctic continent in the past 17 years.
“Our knowledge of geochemical and microbial processes in lightless icy environments, especially at subzero temperatures, has been mostly unknown up until now. This work expands our understanding of the types of life that can survive in these isolated, cryoecosystems and how different strategies may be used to exist in such challenging environments.”
The sampling found that the brine is oxygen-free, slightly acidic, and contains high levels of organic carbon, molecular hydrogen, and both oxidized and reduced compounds. The findings were unexpected because of the extremely salty, dark, cold, isolated ecosystem within the ice.
“Geochemical analyses suggest that chemical reactions between the brine and the underlying sediment generate nitrous oxide and molecular hydrogen,” said Kenig. “The hydrogen may provide some of the energy needed to support microbes.”
“It’s plausible that a life-supporting energy source exists solely from the chemical reaction between anoxic salt water and the rock,” said Dr. Christian Fritsen, a systems microbial ecologist and Research Professor in DRI’s Division of Earth and Ecosystem Sciences.
“If that’s the case, this gives us an entirely new framework for thinking of how life can be supported in cryoecosystems on earth and in other icy worlds of the universe,” Murray said.
“We’d like to go back and find if there is a proper body of brine without ice down there,” said Doran. “We’d also like to get some sediment cores from below that to better establish the history of the lake. In the meantime, we are using radar and other geophysical techniques to probe what lies beneath.”
The finding are described in this week’s issue of the Proceedings of the National Academy of Sciences.