杏吧原创

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.

To their surprise, biochemical tests and electron microscope images show that
the organisms can grow and divide even at 鈥�17 掳C鈥攖he coldest
condition the team tested. 鈥淧robably they could live at even lower
temperatures,鈥� 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 鈥�85 掳C and
鈥�13 掳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鈥攁nd the Antarctic is very dry, because all the water is frozen. 鈥淎t
the South Pole, the repair mechanisms make sense,鈥� 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. 鈥淭he
more extreme conditions that we look at, the more we find that bacteria are able
to survive,鈥� says Carpenter.

Rich Zurek, who worked on NASA鈥檚 Mars Polar Lander programme, says that while
the average temperature at Mars鈥檚 North Pole is only around 鈥�70 掳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 鈥�120 掳C, but Zurek says there is no reason why organisms would
not be able to survive.

鈥淯nder those kind of conditions, life goes dormant. It finds a way to
preserve itself, 鈥� he says.