The phenomenon of cryptobiosis has fascinated humans since it was discovered in tardigrades by Spallanzani in 1776. Today, researchers think that tardigrades could be used as test animals for traveling into outer space. Experiments in which tardigrades in anhydrobiosis (tun stage) are exposed to cosmic radiation, vacuum, and temperatures close to absolute zero have been very successful, and ongoing experiments with ionosphere balloons have shown that both the species Echinis-cus testudo and Richtersius coronifer may be the right test animals for true outer space experiments in space shuttles. The pharmaceutical industry has been very interested in role of the sugar trehalose that tardigrades produce prior to anhy-drobiosis and cryobiosis stages. Trehalose appears to protect the cellular membranes of tardigrades against damage from freezing and dehydration. Trehalose may be used in organ transplantation to avoid freeze damage. Recently, it has become clear that the phenomenon of cryptobiosis is much more complex than first thought. New results show that it is not only trehalose that is responsible for survival during cryobio-sis and anhydrobiosis. In the species Richtersius coronifer, a very large protein (ice-nucleating agent) seems to protect the cellular structures from fast freezing in active animals. The phenomenon of cryptobiosis is a fascinating biological puzzle. By solving the puzzle of how a tardigrade can go into a reversible death (ametabolic stage) for many years, and after a few minutes of rehydration can climb around again, it might explain how life developed on earth.
1. Giant yellow water bear (Richtersius coronifei); 2. Large carnivorous water bear (Milnesium tardigradum); 3. Tidal water bear (Echiniscoides sigismundi sigismundi); 4. Turtle water bear (Echiniscus testudo); 5. Balloon water bear (Tanarctus bubulubus). (Illustration by Amanda Humphrey)
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