The discovery of photoautotrophic microorganisms in permafrost is surprising, not only because of the constant subzero temperature and complete darkness of the sediments, but also because of the length of time the sediments have been frozen. These organisms may well be the only living photoautotrophs that have survived for a geologically significant period of time. These cyanobacteria and green algae inhabiting such an absolutely extreme environment exist "on the edge", near the absolute limits of their physiological potential. Therefore, permafrost cyanobacte-ria and green algae represent unique material for research on evolution and low-temperature adaptation, and they defiantly possess unique mechanisms that allow them to maintain viability for very long periods of time.

Acknowledgments This research was supported by NASA Astrobiology Institute (Cooperative Agreement Number NCC-1274); and by the Russian Foundation of Basic Research (grant 01-05-05-65043).

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