ABSTRACT
Lake Untersee .................................................................... 143 5.5.5 Microorganisms In Situ in Ice Bubbles ............................................ 144
5.6 Relevance of Polar Microbial Extremophiles to Astrobiology ..................... 148 5.7 Summary ...................................................................................................... 148 Acknowledgments .................................................................................................. 149 References .............................................................................................................. 149
Microbial extremophiles are the dominant life forms of the polar environments. They are able to survive in the extreme polar environments and have developed mechanisms that allow them to cope with a variety of stressors. These include freezing temperatures and repeated freeze-thaw cycles, desiccation, high or low levels of salinity or pH, and lengthy periods of darkness during winter. Polar life forms must also be able to survive exposure to high levels of solar UVB (280-314 nm) radiation due to stratospheric ozone depletion over the Antarctic (McKenzie et al., 2003) and Arctic regions during the summer (Knudsen et al., 2005). The dominant prokaryotes of polar environments are psychrophilic and psychrotolerant cyanobacteria, bacteria and archaea, and the dominant photosynthetic eukaryotes are algae, which are primarily diatoms.
