Alien life 22 January 2013

Living on the edge

COSMOS Magazine
Extremophiles can live just about anywhere. Here are our top 10 super survivors.
As the world's toughest bacterium, Deinococcus radiodurans can survive radiation, vacuum, dehydration, intense cold and acid.

1. Feeling the heat

A bacteria so far known only as Strain 121 holds the record for surviving at the highest temperature. It was discovered in 2003 in a water sample from a ‘black smoker’ hydrothermal vent called Finn in the northeast Pacific Ocean, about 320 km off Puget Sound, in the U.S. state of Washington. Not only did it survive high pressure autoclave sterilisation at 121 C, but its cell numbers also doubled over 24 hours at that temperature.

2. Under pressure

Some tardigrades can withstand extremely low pressures, with one species surviving the vacuum of space for 10 days. Others can withstand excessively high pressure – up to 6,000 atmospheres, six times the pressure of water at the bottom of the Mariana Trench, the deepest ocean water.

3. Surviving radiation

Thermococcus gammatolerans, discovered in 2003 in a seafloor hydrothermal vent off the coast of California, is the most radiation resistant organism known to science. It can withstand 30,000 Grays of radiation (a Gray is the absorption of one joule of such energy by 1kg of matter). Five Grays is enough to kill a human.

4. High salinity

The brine shrimp, Artemia salina, can tolerate water almost saturated with salt, and can live several days in solutions of chemicals such as potassium permanganate and silver nitrate.

5. High acidity

Cyanidium caldarium is an alga that thrives in hot acid. It can withstand liquids with pH values of around 2 (indicative of extreme acidity) and is found in waters near geysers in Yellowstone National Park in the US and other volcanic regions.

6. Metal-rich streams

The microbe Ferroplasma acidarmanus is found in streams that drain iron mines, most notably Iron Mountain in California. Apart from the high levels of metals it can withstand, F. acidarmanus can also endure extreme acidity. It is considered to have high potential to be adapted for extracting ores, especially iron, from polluted mine streams.

7. Extreme cold

On the cold front, the microbe Psychrobacter arcticus has been isolated from sea-ice and Antarctic glaciers. One strain, 273-4, was found in a Siberian permafrost core more than 20,000 years old. According to Cornell University’s Peter Bergholz, one of the team investigating the find, the bugs were not hibernating but growing and dividing, albeit very slowly.

8. Strong electricity

The electric eel, Electrophorus electricus, is not a standard candidate for inclusion in the extremophile top 10. But, as NASA’s Lynn Rothschild points out, it can produce strong electric currents and therefore must be able to tolerate them.

9. Low acidity

The tiny archaea of the genus Natronobacterium can survive in highly alkaline waters. It was first identified in samples taken from Lake Magadi, Kenya, the waters of which are a brine of sodium carbonate. For most of the year the lake has an 80% covering of soda.

10. All-round bruiser

Deinococcus radiodurans is listed in The Guinness Book Of World Records as the world’s toughest bacterium. It was discovered by researchers trying to sterilise meat with a dose of radiation they thought would kill all known forms of life. But the meat subsequently spoiled and D. radiodurans was found to be the culprit. It can also survive a vacuum, dehydration, intense cold and acid.

Robin McKie is a COSMOS contributing editor and science and technology editor for The Observer.

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