Tuesday, February 5, 2013

MICROBIAL LIFE FOUND IN FROZEN BRINE OF ICE-SEALED LAKE IN ANTARCTICA


Within Lake Vida’s freezing waters, diverse microbial life is using different strategies to survive. The Lake is permanently covered by a cap of ice up to 27 metres thick, is six times saltier than normal sea water and is one of the coldest aquatic environments on Earth at −13 °C. The lake contains no oxygen, has slightly acidic (pH 6.2) sodium chloride-dominated brine, is mostly frozen and possesses the highest nitrous oxide levels of any natural water body on Earth.

Scientists, including Dr. Alison Murray and Dr. Christian Fritsen of Nevada’s Desert Research Institute (DRI), have been drilling into the lake and have discovered a large amount of different kinds of bacteria. The lake is the largest of a number of small bodies of water within the McMurdo Dry Valleys Antarctic desert. The team has drilled into Lake Vida twice: the first time was 2005 and then again in 2010. They drilled out cores of ice from the lake, collected samples of the brine from the frozen material, and assessed the water's potential for harbouring life.

The water samples from both of the trips displayed about one-tenth of the abundance of cells usually found in freshwater lakes in moderate climate zones. Some of the cells were up to 1 micrometre in diameter but within the samples many more particles were around 0.2 micrometres in diameter. None of the cells represent previously unknown life forms; genetic analysis suggested that most of the cells were related to known types of bacterium. There is however one bacterium of normal size amongst the others that seems to have no close relation to cultivated bacteria; it may represent a new phylum.

The team have not worked out how the bacteria produce energy though there are a couple of theories. One theory is that the bacteria may emulate some known bacteria by only living off dissolved organic carbon; another is that the bacteria may use more exotic forms of energy, like microbes that live in extreme environments. There is a lot of energy within the brine and though carbon is believed to be the main energy source, hydrogen may be the key ingredient to sustaining the lake’s microbial community in the long-term. The abundance of different chemical compounds present in the lake suggests that chemical reactions are taking place between the brine and the underlying iron-rich sediments, producing the nitrous oxide and molecular hydrogen.

 The ice cap over the lake has been shown to be growing upwards from the melt-water provided by surrounding glaciers which flows over the ice and refreezes. Isotopic analysis of the organic carbon particles in the ice suggests the lake has been sealed for about 2,800 years. This in turn suggests that the carbon in the brine must have been there for at least that long and there is likely not much of it, meaning the microbes must be using something else to produce energy. The microbes are isolated and there are no predators in the lake; indicating that the cells may be at ‘survival mode’, without cell division and reproduction to allow them to survive the harsh environments for a long time.

As Lake Vida is ice-sealed, its geochemistry and biology is likely to be very different from other Antarctic subglacial rivers and lakes. Three Antarctic subglacial lakes are about to be sampled: Ellsworth, Whillans and Vostok (read about Vostok herehttp://on.fb.me/11itBob). Looking at what lives in these subglacial waters will give scientists more information as to what conditions are needed to support life on Earth and on other planetary bodies within the solar system. There is evidence that Jupiter’s moon Europa contains pockets of slushy ice and liquid water beneath its icy shell; these findings may have implications for potential life there.

Lake Vida has not been isolated for as long as the subglacial lakes, though the discovery of diverse microbial life within it is significant, as it is yet another extreme environment where life has been found. The extreme saltiness of Lake Vida also marks a difference.

The image is of the research field camp on Lake Vida, located in Victoria Valley, the northern most of the McMurdo Dry Valleys.


http://www.nature.com/news/life-abounds-in-antarctic-lake-sealed-under-ice-1.11884
http://www.bbc.co.uk/news/science-environment-20501574
http://www.pnas.org/content/early/2012/11/21/1208607109
Image credit: Photo Courtesy Desert Research Institute, Alison Murray



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