CRYOBIONTS IN SNOW AND ICE OBSERVED WITH LOW TEMPERATURE SCANNING ELECTRON MICROSCOPY (SEM) AND TRANSMISSION ELECTRON MICROSCOPY (TEM)

Numerous studies have isolated and identified hundreds of species of nival fauna. Some of these species were true cryobionts that inhabited adverse alpine environments others were merely aeolian fauna that were passively deposited on snowfields by updrafts. Because of the extreme environments in which these organisms are found, studying them in situ is very difficult. However, because similar environments may exist or previously existed on Mars, the growth of analogous fauna could be/have been supported in the Martian milieu. For this reason, identifying these organisms and understanding the ultrastructural features that enable them to survive in adverse environments is an important endeavor. Recently, our laboratory has been successful in sampling, shipping, storing and imaging snow crystals and ice grains with a technique known as low temperature SEM. Briefly, this technique consists of collecting samples at remote sites and freezing them in liquid nitrogen. All further manipulations, including imaging, are performed at near liquid nitrogen temperatures, thereby insuring that no re-crystallization or sublimation can occur. At several of the collection sites, bacteria, fungi, algae and ice worms were unexpectedly included with the snow and ice samples. As a result, the surface features of these frozen organisms could be observed in true three-dimensions at magnifications of 50,000 times. Furthermore, following imaging in the SEM, algae could be recovered and chemically fixed by freeze-substitution for examination in a TEM where observations revealed the internal ultrastructural features of the cells. We believe that these results demonstrate important new techniques for in situ studies of nival fauna.