Cold but alive

The ice in the polar seas seems to be an impossible place for life. Although polar bears and penguins roam its vast surface and fish and seals swim underneath, the ice itself seems to nothing more than water frozen solid. But it's actually much more.

Life swarms in tiny channels within the polar ice, full of bacteria, fungi, algae, flat worms and small crustaceans. The hollow spaces are often only as small as a strand of hair and are filled with extremely salty water. If the water were to freeze, the salt would no longer be contained in the ice.

Temperatures of minus 20 degrees Celsius (-4 degrees Fahrenheit) are common, posing a danger for the inhabitants of the hollow spaces in polar ice. Once frozen, these inhabitable cavities disappear. This situation would be similar to a person standing in a room watching the walls move toward each other. But polar ice survivors master all these difficulties.

Many organisms living in polar ice produce proteins that protect them from freezing and release these in the polar water. The proteins bond to developing ice crystals and prevent them from growing further.

Anti-freeze protein

The single-celled diatom, called Fragilariopsis cylindrus, produces a particularly remarkable antifreeze protein. That is a discovery of a team of researchers at the Alfred-Wegener-Institute for Polar and Ocean Research in Bremerhaven. The protein alters not only the size but also the inner structure of the ice crystal and thus the porosity of ice.

"We assume that ice changes so significantly in this way that the salt will not wash out," said Maddalena Bayer-Giraldi, a researcher at the institute. "It remains in the channels, making it difficult for the small passages and cavities in the ice to freeze."

Because of the protein, the ice doesn't grown into a stable block but rather into a loose network of ice crystals full of tiny cavities and passages , offering inhabitable space for algae. The researchers have determined that Fragilariopsis cylindrus produces a huge amount of protein when surrounded by severe cold and salty conditions.

Many polar ice inhabitants use another trick: they discharge slimy substances, such as polymeric sugar molecules that form a protective shell around them. These buffer the organisms against the rest of their environment, similar to a wetsuit for diving, which prevents the rapid exchange of water on the skin.

Not only the ice but also the extreme cold itself is very hard on the organisms. The membranes of the cells become stiff and brittle and thus inoperative. Consequently, polar ice inhabitants produce huge amounts of unsaturated fatty acids in the membranes that make them soft and supple.

Cold significantly slows the metabolism rate. While the enzymes function at low temperatures, the work of the protein cells becomes slower or stops completely. The special enzymes of the polar ice inhabitants have adjusted to the low temperatures in the course of their evolution and work efficiently in the bitter cold.

Millions of years of evolution

There are, however, essential proteins that after millions of years of evolution are still unable to adjust to the cold. But those that survive produce more than the others. It has been proved that many enzymes working slowly can create as much as fewer enzymes that rush.

Polar ice inhabitants have another problem to solve, too: the extremely high salt content in their environment. This content is generally harmful to living things. If much more salt is present outside of the organism than inside, water follows from the cells to the outside to dilute and to balance the salt concentrations inside and outside. Too little water inside the cell means death.

That's why these survival artists trick the lat of nature. They produce many molecules that they accumulate inside, such as the amino acid proline, the sugar-like compound mannitol and others. These substances also require being diluted like the salt outside. Therefore the water remains in the cell and the balance is restored.

Finding a niche

Darkness dominates the poles for at least half a year. But even with the sun shines, little light penetrates in the dwellings of the polar ice inhabitants, especially when the ice is very thick and covered by a layer of snow.

Many organisms that require photosynthesis to live, such as algae, have adapted biochemically to the low-light conditions and produce either very effective light-harvesters or a huge quantities of the required substances. And they can decide how they want to eat. In the six months of deep darkness, they switch from photosynthesis and nourish themselves with nutrients that the water has washed into their small salt-water passages.

With many different kinds of tricks, bacteria, algae, crabs and other species have managed to conquer an ecological niche that seems uninhabitable at first glance.

Author: Brigitte Osterath / jrb
Editor: Jessie Wingard