Survival under space vacuum--biochemical aspects.

Exposure to vacuum predominantly causes the removal of water. As a consequence hydrophobic bonds (e.g. of membranes and proteins) are disrupted and metabolism practically comes to a complete halt. Removal of hydrate water also causes substantial changes regarding the structure of DNA (A-structure likely prevails). Some organisms, however, especially bacterial spores and fungal conidia are so well adapted to extreme dryness that substantial fractions of these organisms survive several months of vacuum even at room temperature. In these organisms some vacuum-induced alterations occur that are not readily reversed by readdition of water; mutations become evident and the amount of DNA covalently bound to protein is drastically increased. The mechanisms of these processes and their possible repair are not yet clear. There is evidence that chemical reactions (e.g. dehydration reactions) are involved although they likely proceed at an extremely low rate. Using the dehydration of serin by vacuum as a model system (the resulting amino acrylic acid is converted into pyruvic acid and ammonia after reexposure to water) we could establish that about 3 out of 100 000 serins are finally converted into pyruvic acid after exposure to 10(-6) Torr for 1 week at 55 degrees C In dry Ar the corresponding rate is only about 1.5.