Blood Falls
Trapped under ice for 1.5 million years, life still thrives
Published 17 April, 2009, 12:10
A study of a saltwater lake sealed under an Antarctic glacier has shown how bacteria found a unique mechanism to survive in the harsh conditions.
It is not uncommon for microbial life to adapt to extreme environments from hot geothermal springs to the depths of the ocean. Antarctica’s subglacial lakes have been sparking microbiologists’ interest ever since their discovery in the late 1960s. However, studying them is very challenging from a technical point of view, because it requires drilling through hundreds of meters of ice and special precautions to avoid contaminating their fragile ecosystems.
In the case of the subglacial lake, which has been trapped for at least 1.5 million years half a kilometer under Taylor Glacier's in Antarctica's Dry Valleys, scientists have had more luck. Every summer a flow from it trickles at the glacier’s end, quickly turning its color to intense rusty red as the water is rich in oxides and contact with fresh air causes the color change. For that reason it is known as the ‘Blood Falls’.
A group of researchers at Dartmouth College, led by microbiologist Jill Mikucki, have been studying samples of the water for over six years, discovering a peculiar ecosystem in the ice-cold salt waters. The lake receives no light and has almost no oxygen in it, so the community of at least 17 different microorganisms inhabiting it has developed a unique mechanism for respiration.
All living organisms use a chain of chemical reactions to transform nutrients into a form that can be used by their cells to generate energy. In the process, electrons spurring from the dissection of complex molecules into simpler ones must be transferred to some final oxidizing agent, which is usually oxygen. Exotic microorganisms can use other substances as electron acceptors, including sulphate or metal ions.
This was true for the bacteria living under the Taylor Glacier. Mikucki and her team believe iron was the final destination of their electron transport chain, and they use sulphate as catalyst. Not only has this mechanism never encountered before, but also scientists doubted it was even possible, because iron and sulphate would just react together to make the inert mineral iron pyrite. The study published in Science magazine suggests the subglacial microbes found a way around this.
"I think this is a fantastic study," said Alan Kaufman, a biogeochemist at the University of Maryland, College Park. It presents "a spectacular new environment that we can explore to understand life on the edge."
The discovery may explain how life on the planet survived during the so-called ‘Snowball Earth’ period, a hypothetical age some 600 to 800 million years ago when glaciers covered most of its surface. It may also suggest that life can be encountered in extra-terrestrial environments like under the surface of Mars or on Jupiter's icy moon Europa.
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