Researchers Identify Lowest Temperature Limit for Basic Life on Earth

New research from the British Antarctic Survey suggests that the lowest possible temperature at which simple life can survive is minus 20 degrees Celsius.

The researchers, who published their work in the journal PLOS One, suggest that at temperatures below -20 C single-celled organisms dehydrate, taking on a vitrified "glass-like" state that prevents them from completing their life cycle.

Because reproduction ceases at temperatures below -20 C, the researchers contend that -20 C is the lowest temperature limit for basic life on Earth.

In their experiments, the researchers found that as the temperate of water in which they were studying single-celled organisms was lowered further and further below freezing, the water within the organisms began to seep out to form more ice, leaving the cells not only dehydrated, but vitrified into a glass-like state where reproduction is not possible. When cells are unable to reproduce, the scientists considered them no longer living, even though they can be brought back to life by raising the temperature.

The researchers say this state of vitrification is similar to the state of dried-out plant seeds.

"The interesting thing about vitrification is that in general a cell will survive, where it wouldn't survive freezing, if you freeze internally you die. But if you can do a controlled vitrification you can survive," said lead study author Andrew Clarke of British Antarctic Survey in a news release by the Natural Environment Research Council. "Once a cell is vitrified it can continue to survive right down to incredibly low temperatures. It just can't do much until it warms up."

More complex organisms, like humans, plants and animals, are to some extent able exert more control over their environment than simple organisms.

"Bacteria, unicellular algae and unicellular fungi - of which there are a huge amount in the world - are free-living because they don't rely on other organisms," Clarke explained.

"Everything else, like trees and animals and insects, has the ability to control the fluid that surrounds their internal cells. In our case it's blood and lymph. In a complicated organism the cells sit in an environment that the organism can control. Free-living organisms don't have this; if ice forms in the environment they are subject to all the stresses that implies."

After testing a number of single-celled organisms, all of which vitrified below -20 C, the researchers contend that unicellular life simply cannot grow below -20 C, without exception.

The find helps explain why deep-freezing food can preserve it from getting moldy.

"We were really pleased that we had a result which had a wider relevance, as it provided a mechanism for why domestic freezers are as successful as they are," Clarke said.