Lichens, cyanobacteria and molds growing in humidity of simulated Martian atmosphere: Difference between revisions
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Any photosynthetic life on Mars would have to cope with the strong UV light, which is not much filtered by the thin Mars atmosphere. The lichens studied in these experiments have protection from UV light due to special pigments only found in lichens, such as parietin and antioxidants such as b-carotene in epilithic lichens. This gives them enough protection to tolerate the light levels in conditions of partial shade in the simulation chambers and make use of the light to photosynthesize. Because of their importance for survival in such conditions, UV protection pigments have been suggested as potential biomarkers to search for on Mars.<ref>"Solar radiation is the primary energy source for surface planetary life, so that pigments are fundamental components of any surface-dwelling organism. They may therefore have evolved in some form on Mars as they did on Earth." {{cite journal | doi = 10.1017/S1473550402001039 | volume=1 | pages=39 | title=Pigmentation as a survival strategy for ancient and modern photosynthetic microbes under high ultraviolet stress on planetary surfaces | year=2002 | journal=International Journal of Astrobiology | last1 = Wynn-Williams | first1 = D.D. | last2 = Edwards | first2 = H.G.M. | last3 = Newton | first3 = E.M. | last4 = Holder | first4 = J.M.| bibcode=2002IJAsB...1...39W }}</ref> |
Any photosynthetic life on Mars would have to cope with the strong UV light, which is not much filtered by the thin Mars atmosphere. The lichens studied in these experiments have protection from UV light due to special pigments only found in lichens, such as parietin and antioxidants such as b-carotene in epilithic lichens. This gives them enough protection to tolerate the light levels in conditions of partial shade in the simulation chambers and make use of the light to photosynthesize. Because of their importance for survival in such conditions, UV protection pigments have been suggested as potential biomarkers to search for on Mars.<ref>"Solar radiation is the primary energy source for surface planetary life, so that pigments are fundamental components of any surface-dwelling organism. They may therefore have evolved in some form on Mars as they did on Earth." {{cite journal | doi = 10.1017/S1473550402001039 | volume=1 | pages=39 | title=Pigmentation as a survival strategy for ancient and modern photosynthetic microbes under high ultraviolet stress on planetary surfaces | year=2002 | journal=International Journal of Astrobiology | last1 = Wynn-Williams | first1 = D.D. | last2 = Edwards | first2 = H.G.M. | last3 = Newton | first3 = E.M. | last4 = Holder | first4 = J.M.| bibcode=2002IJAsB...1...39W }}</ref> |
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Most lichens do not survive prolonged exposure to Mars surface conditions. But an experiment simulating a Mars environment in a small chamber external to the ISS as part of [[EXPOSE#EXPOSE-E results|Expose-E]] in 2008-2009 showed that one lichen, Xanthoria elegans, retained a viability of 71% for the algae (photobiont) and 84% for the fungus (mycobiont) after 18 months inn Mars surface simulation conditions. Moreover, those surviving cells returned to 99% photosynthetic capabilities on return to Earth. |
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This was an experiment without the day night temperature cycles of Mars and the lichens were kept in a desiccated state so it didn't test their ability to survive in niche habitats on Mars. This greatly exceeded the post flight viability of any of the other organisms tested in the experiment.<ref name="Brandtde Vera2014">{{cite journal|url=http://elib.dlr.de/90411/1/Annette-Brandt-download.php.pdf|last1=Brandt|first1=Annette|last2=de Vera|first2=Jean-Pierre|last3=Onofri|first3=Silvano|last4=Ott|first4=Sieglinde|title=Viability of the lichen Xanthoria elegans and its symbionts after 18 months of space exposure and simulated Mars conditions on the ISS|journal=International Journal of Astrobiology|year=2014|pages=1–15|issn=1473-5504|doi=10.1017/S1473550414000214|volume=14|issue=3|bibcode=2015IJAsB..14..411B}}</ref> |
This was an experiment without the day night temperature cycles of Mars and the lichens were kept in a desiccated state so it didn't test their ability to survive in niche habitats on Mars. This greatly exceeded the post flight viability of any of the other organisms tested in the experiment.<ref name="Brandtde Vera2014">{{cite journal|url=http://elib.dlr.de/90411/1/Annette-Brandt-download.php.pdf|last1=Brandt|first1=Annette|last2=de Vera|first2=Jean-Pierre|last3=Onofri|first3=Silvano|last4=Ott|first4=Sieglinde|title=Viability of the lichen Xanthoria elegans and its symbionts after 18 months of space exposure and simulated Mars conditions on the ISS|journal=International Journal of Astrobiology|year=2014|pages=1–15|issn=1473-5504|doi=10.1017/S1473550414000214|volume=14|issue=3|bibcode=2015IJAsB..14..411B}}</ref> |
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