Microbes in the Alaskan permafrost have been found living in temperatures as low as minus 40 degrees Celsius.
Typically bacteria in the permafrost are in a dormant state
The discovery raises concerns that the activity of these bacteria, once thought inactive at such extreme temperatures, could be making a considerable contribution to greenhouse gas production.
Scientists found that bacteria taken from the Alaskan tundra soil release gases during energy production whilst apparently in a frozen state.
This runs contrary to textbook biology, which dictates the need for freely available water to allow these single-celled life forms to function.
Dr Nicolai Panikov, from the Stevens Institute of Technology, New Jersey, US, and colleague, Dr Vladimir Romanovsky, from the University of Alaska, tested the mixture of bacteria and registered the production of gases; by-products of metabolism.
"Typically, bacteria in the permafrost are in a dormant state but we have found that they reproduce very slowly and respire producing gases including CO2 and methane when frozen," Dr Panikov said.
Water is considered essential for life, whether at the single-cell level, such as in bacteria, or in larger animals. It helps the exchange of essential gases between the bacteria and the outside.
So the discovery of bacteria, thought to be frozen solid at such extreme temperatures, raises many interesting questions about the survival mechanisms used in these harsh conditions.
"We have found that it is not pure ice but the mixture of ice and mineral particles that allows for the exchange of gases," Dr Panikov told BBC News website.
"One explanation is that the bacteria oxidise substances in the permafrost to generate heat inside themselves or that these microbes create anti-freeze compounds that keep water liquefied inside their cells."
Permafrost covers about one fifth of the world's land surface and is frozen over most of Alaska, Northern Canada and Siberia, from depths of a few centimetres to 300m (1,000ft). Long considered a major carbon sink, recent evidence suggests that the permafrost is thawing as global temperatures rise.
Even a small increase in temperature will have a significant increase on the rate of metabolic activity in these bacteria affecting the biochemistry of the soil.
If the activity of these bacteria was incorporated into models of climate change prediction, the permafrost may take on the role of a source of greenhouse gases rather than a sink.
"Our results predict the rate of actual degradation- it shows that it's not necessary for the temperature to rise to freezing point for the stimulation of the degradation process," said Dr Panikov.
EARTH'S FROZEN GROUND
Permafrost is permanent year-round frozen ground
Soils many cm below surface never rise above 0C
Only top few cm thaw in summer - "active layer"
Many regions have been like this for 1,000s of years
Major thaw changes water distribution in ecosystem
Sequestered carbon released; buildings destabilised
Knut Stamnes, Professor of atmospheric physics at Stevens, believes that as the permafrost thaws the greatest threat comes from methane.
"Methane is more important than CO2 in producing greenhouse gases because the atmosphere is relatively saturated with CO2 but not with methane yet. This is a new area for exploration." said Professor Stamnes.
Life forms on other planets
In fact, methane gas was recently found by the European Space Agency (Esa) Mars Express mission in the lower atmosphere of the Red Planet and has been associated with ground ice, fuelling speculation about a biological source of the methane.
Professor Dawn Sumner, associate professor of geology at the University of California-Davis, advises the US space agency (Nasa) Mars Exploration and Analysis Group.
Permafrost covers about one fifth of the world's land surface
She believes that the 2007 Phoenix Lander mission to Mars will have increased access to potentially habitable zones and that if life does exist, it is likely to be found in ice first.
"Panikov's results could extend our concept of possible habitable zones to colder temperatures than previously envisioned," said Professor Sumner.
"If low temperature life does exist on another planet, we are likely to find it in ice first because we have identified many very cold, icy environments, but very few environments with liquid water, especially ones that are accessible to robotic missions."
More details on the bacteria research are due to be published in the Soil Biology & Biochemistry journal.