Life at the cold extreme


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<!--intro-->Life exists even at the South Pole, one of the most inhospitable places on Earth.

Microbiologist Ed Carpenter of the State University of New York in Stony Brook and his colleagues have found between 200 and 5000 bacteria per millilitre of melted snow from the pole.<!--/intro-->

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To their surprise, biochemical tests and electron microscope images show that the organisms can grow and divide even at ­-17 °C--the coldest condition the team tested. "Probably they could live at even lower temperatures," says Carpenter.

Although bacteria have been found in the snow near the pole before, they were thought to have blown in accidentally. No one believed they could grow in the harsh conditions there, where temperatures range between ­-85 °C and ­-13 °C.

DNA tests revealed that all the bacteria are previously unknown species. Their closest relatives are a group called Deinococcus, which are known for their extremely efficient DNA repair mechanisms.

It was not known why the Deinococcus evolved such high protection, since nowhere on Earth is ultraviolet radiation strong enough to damage DNA so badly. However, severe desiccation can harm DNA just as much as UV radiation does--and the Antarctic is very dry, because all the water is frozen. "At the South Pole, the repair mechanisms make sense," says Carpenter.

The finding suggests that life could exist in other environments previously thought too harsh, such as the polar ice cap on Mars, the researchers say. "The more extreme conditions that we look at, the more we find that bacteria are able to survive," says Carpenter.

Rich Zurek, who worked on NASA's Mars Polar Lander programme, says that while the average temperature at Mars's North Pole is only around ­70 °C in summer, local areas of volcanic activity or hot springs might have provided enough warmth for life to evolve. In the Martian winter, temperatures fall to around ­-120 °C, but Zurek says there is no reason why organisms would not be able to survive.

"Under those kind of conditions, life goes dormant. It finds a way to preserve itself, " he says.

More at: Applied and Environmental Microbiology (vol 66, p 4514)

Joanna Marchant

From New Scientist magazine, 11 November 2000.