Assessment of Planetary Protection Requirements for Mars Sample Return Missions (2009) / Chapter Skim
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3 Advances in Microbial Ecology
3 Advances in Microbial Ecology
Pages 32-36
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From page 32... ...
A substantial and growing body of evidence shows that life not only is present, but also frequently thrives under extreme environmental conditions.1 The known limits of life now extend from superheated deep ocean hydrothermal vents, to ice-brine environments of polar regions, from highly acidic waters of mine drainage systems, to ephemeral, hypersaline alkaline and acidic lakes, from sunlit surface environments, to perpetually dark subsurface aquifers located thousands of meters underground. Even more remarkably, biologists continue to discover new biological entities, such as the giant Acanthamoeba polyphaga mimivirus;2 virophages that prey on other viruses;3 and novel single-species ecosystems, such as the deep subsurface bedrock fractures inhabited solely by the chemoautotrophic Candidatus Desulforudis audaxviator.4 EXAMPLES OF LIFE IN EXTREME ENVIRONMENTS ON EARTH The broad range of environmental extremes capable of sustaining terrestrial life is surpassed only by the physiological, metabolic, and phylogenetic diversity of their extremophile inhabitants (Table 3.1)
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From page 33... ...
.12 Conversely, viable organisms have been retrieved from ancient salt crystals dated at 250 million years old,13,14 as well as from antarctic and siberian permafrost believed to be millions of years old.15,16,17 The combined effect of salts and ice is a dramatic reduction of water activity (aw) , which is now considered to permit the maintenance of metabolism at aw = 0.3.18 This level is considerably lower than previous estimates of aw ~ 0.61 for the water activity limit of biological activity.19 Regardless, the precise impact of extreme low temperature and water activity stress (or other physicochemical environmental parameters for that matter)
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From page 34... ...
20 Less well appreciated is the fact that microorganisms living in a variety of mineralizing environments protect themselves against high doses of ultraviolet radiation with biomediated mineral coatings (e.g., silica, iron oxides, and so on; Figure 3.1) .21 Similarly, endolithic microorganisms -- i.e., those residing within the interior spaces of porous rocks and sediments -- are afforded protection from radiation, desiccation, and extreme fluctuations of temperature by enclosing mineral matrices.22 FIGURE 3.1 Transmission electron micrographs of3.1_from word.epscoatings that can form around microorganisms the biomediated mineral in mineralizing environments.
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From page 35... ...
• The discovery in deep subsurface environments on Earth of microbial ecosystems that are able to survive on inorganic sources of energy has greatly enhanced the prospect of chemoautotrophic life in subsurface environments on Mars. • Studies have confirmed the potential for the long-term viability of terrestrial microorganisms captured in deposits of some extreme terrestrial environments (e.g., ices and evaporates)
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From page 36... ...
and G.P. Landis, "Formation of Patterned Ground and Sublimation Till Over Miocene Glacier Ice in Beacon Valley, Southern Victoria Land, Antarctica," Geological Society of America Bulletin 114:718-730, 2002.
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