Lichens, cyanobacteria and molds growing in humidity of simulated Martian atmosphere: Difference between revisions
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The experimenters concluded that these black fungi can survive in a Mars environment.<ref name="ZakharovaMarzban2014">{{cite journal|url=http://www.nature.com/srep/2014/140529/srep05114/full/srep05114.html|last1=Zakharova|first1=Kristina|last2=Marzban|first2=Gorji|last3=de Vera|first3=Jean-Pierre|last4=Lorek|first4=Andreas|last5=Sterflinger|first5=Katja|title=Protein patterns of black fungi under simulated Mars-like conditions|journal=Scientific Reports|volume=4|pages=5114|year=2014|issn=2045-2322|doi=10.1038/srep05114|pmid=24870977|pmc=4037706|quote="The results achieved from our study led to the conclusion that black microcolonial fungi can survive in Mars environment."|bibcode=2014NatSR...4E5114Z}}</ref>
===Effects of micropores in salt pillars===
In experimental studies of salt pillars in the Atacama desert, microbes are able to access liquid at extremely low relative humidities due to micropores in the salt structures. They do this through spontaneous capillary condensation, at relative humidities far lower than the deliquescence point of NaCl of 75%.<ref>{{cite web|last1=Bortman|first1=Henry|title=Islands of Life, Part V|url=http://www.astrobio.net/topic/origins/extreme-life/islands-of-life-part-v/|website=Astrobiology Magazine (NASA)|date=Jul 25, 2011}}</ref>
[[File:Salt Pillars - Atacama Desert.jpg|thumb|400 px|'The Atacama desert hosts the closest analogue of what a real, live Martian might be like', in its salt rock formations.<ref>{{cite web|last1=Davies|first1=Paul|title=The key to life on Mars may well be found in Chile|url=https://www.theguardian.com/commentisfree/2012/aug/03/life-mars-chile|website=The Guardian|date=Aug 3, 2012}}</ref>]]
Micro-environmental data measured simultaneously outside and inside halite pinnacles in the Yungay region (table 2 from <ref name="WierzchosDavila2012"/>)
{| class="wikitable"
|-
!Variable !! Halite exterior !! Halite interior
|-
| Mean annual RH, % || 34.75 || 54.74
|-
| Maximum annual RH, % || 74.20 || 86.10
|-
| Minimum annual RH, % || 2.90 || 2.20
|}
The researchers, Wierzchos et al., did detailed studies with scanning electron microscopes. At 75% relative humidity then brine was abundant inside the salt pillars. As the humidity was reduced, even at 30% RH, the cyanobacteria aggregates shrunk due to water loss, but still there were small pockets of brine in the salt pillars.<ref name="WierzchosDavila2012">{{cite journal|url=http://www.biogeosciences.net/9/2275/2012/bg-9-2275-2012.pdf|last1=Wierzchos|first1=J.|last2=Davila|first2=A. F.|last3=Sánchez-Almazo|first3=I. M.|last4=Hajnos|first4=M.|last5=Swieboda|first5=R.|last6=Ascaso|first6=C.|title=Novel water source for endolithic life in the hyperarid core of the Atacama Desert|journal=Biogeosciences|volume=9|issue=6|year=2012|pages=2275–2286|issn=1726-4189|doi=10.5194/bg-9-2275-2012|bibcode=2012BGeo....9.2275W}}</ref>
{{quote|"Endolithic communities inside halite pinnacles in the Atacama Desert take advantage of the moist conditions that are created by the halite substrate in the absence of rain, fog or dew. The tendency of the halite to condense and retain liquid water is enhanced by the presence of a nano-porous phase with a smooth surface skin, which covers large crystals and fills the larger pore spaces inside the pinnacles... Endolithic microbial communities were observed as intimately associated with this hypothetical nano-porous phase. While halite endoliths must still be adapted to stress conditions inside the pinnacles (i.e. low water activity due to high salinity), these observations show that hygroscopic salts such as halite become oasis for life in extremely dry environments, when all other survival strategies fail.<br><br>Our findings have implications for the habitability of extremely dry environments, as they suggest that salts with properties similar to halite could be the preferred habitat for life close to the dry limit on Earth and elsewhere. It is particularly tempting to speculate that the chloride-bearing evaporites recently identified on Mars may have been the last, and therefore most recently inhabited, substrate as this planet transitioned from relatively wet to extremely dry conditions"}}
Microbes also inhabit Gypsum deposits (CaSO<sub>4</sub>.2H<sub>2</sub>O), however Gypsum doesn't deliquesce. Researchers found that the regions of the desert that had microbial colonies within the gypsum correlated with regions with over 60% relative humidity for a significant part of the year. They also found that the microbes imbibed water whenever the humidity increased above 60% and gradually became desiccated when it was below that figure.<ref name="WierzchosCámara2011">{{cite journal|url=https://www.researchgate.net/profile/Alfonso_Davila/publication/45797377_Microbial_colonization_of_Ca-sulfate_crusts_in_the_hyperarid_core_of_the_Atacama_Desert_implications_for_the_search_for_life_on_Mars/links/0912f50e37831ae515000000.pdf|last1=Wierzchos|first1=J.|last2=Cámara|first2=B.|last3=De Los Ríos|first3=A.|last4=Davila|first4=A. F.|last5=Sánchez Almazo|first5=I. M.|last6=Artieda|first6=O.|last7=Wierzchos|first7=K.|last8=Gómez-Silva|first8=B.|last9=Mckay|first9=C.|last10=Ascaso|first10=C.|title=Microbial colonization of Ca-sulfate crusts in the hyperarid core of the Atacama Desert: implications for the search for life on Mars|journal=Geobiology|volume=9|issue=1|year=2011|pages=44–60|issn=1472-4677|doi=10.1111/j.1472-4669.2010.00254.x|pmid=20726901}}</ref>
==References==
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Revision as of 13:03, 22 September 2018
![](https://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Martian_conditions_in_miniature_%287494313830%29_%282%29.jpg/300px-Martian_conditions_in_miniature_%287494313830%29_%282%29.jpg)
A series of experiments by DLR (German aerospace company) in Mars simulation chambers and on the ISS show that some Earth life (Lichens and strains of chrooccocidiopsis, a green algae) can survive Mars surface conditions and photosynthesize and metabolize, slowly, in absence of any water at all. They could make use of the humidity of the Mars atmosphere.[1][2][3][4][5] Though the absolute humidity is low, the relative humidity at night reaches 100% because of the large day / night swings in atmospheric pressure and temperature. This is relevant to the search for native life on Mars and also to planetary protection, the need to protect Mars from Earth life if we wish to study native life in the habitats in its original state.
Lichens relying on 100% night time humidity
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. Indeed, UV protection pigments have been suggested as potential biomarkers to search for on Mars.[6]
An experiment on the ISS as part of 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 in the ISS, in Mars surface simulation conditions, and the surviving cells returned to 99% photosynthetic capabilities on return to Earth. 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.[7]
Another study in 2014 by German aerospace DLR in a Mars simulation chamber used the lichen Pleopsidium chlorophanum. This lives in the most Mars like environmental conditions on Earth, at up to 2000 meters in Antarctica. It is able to cope with high UV, low temperatures and dryness. It is mainly found in cracks, where just a small amount of scattered light reaches it. This is probably adaptive behaviour to protect it from UV light and desiccation. It remains metabolically active in temperatures down to -20 C, and can absorb small amounts of liquid water in an environment with ice and snow.
When exposed to full UV levels in a 34-day experiment in a Mars simulation chamber at DLR, the fungus component of the lichen Pleopsidium chlorophanum died, and it wasn't clear if the algae component was still photosynthesizing.
However, when partially shaded from the UV light, as for its natural habitats in Antarctica, both fungus and algae survived, and the algae remained photosynthetically active throughout. Also new growth of the lichen was observed. Photosynthetic activity continued to increase for the duration of the experiment, showing that the lichen adapted to the Mars conditions.
This is remarkable as the fungus is an aerobe, growing in an atmosphere with no appreciable amount of oxygen and 95% CO2. It seems that the algae provides it with enough oxygen to survive. The lichen was grown in Sulfatic Mars Regolith Simulant - igneous rock with composition similar to Mars meteorites, consisting of gabbro and olivine, to which quartz and anhydrous iron oxide hematite (the only thermodynamically stable iron oxide under present day Mars conditions) were added. It also contains gypsum and geothite, and was crushed to simulate the martian regolith. This was an ice free environment. They found that photosynthetic activity was strongly correlated with the beginning and the end of the simulated Martian day. Those are times when atmospheric water vapour could condense on the soil and be absorbed by it, and could probably also form cold brines with the salts in the simulated martian regolith. The pressure used for the experiment was 700 - 800 Pa, above the triple point of pure water at 600 Pa and consistent with the conditions measured by Curiosity in Gale crater.[8]
The experimenters concluded that it is likely that some lichens and cyanobacteria can adapt to Mars conditions, taking advantage of the night time humidity, and that it is possible that life from early Mars could have adapted to these conditions and still survive today in microniches on the surface.[9]
Black fungi and black yeast relying on 100% night time humidity
In another experiment, by Kristina Zakharova et al., two species of microcolonial fungi – Cryomyces antarcticus and Knufia perforans - and a species of black yeasts–Exophiala jeanselmei were found to adapt and recover metabolic activity during exposure to a simulated Mars environment for 7 days. They depended on the temporary saturation of the atmosphere with water vapour like the lichens. The fungi didn't show any signs of stress reactions (such as creating unusual new proteins).
There Cryomyces antarcticus is an extremophile fungi, one of several from Antarctic dry deserts. Knufia perforans is a fungi from hot arid environments, and Exophiala jeanselmei is a black yeast endolith closely related to human pathogens.
The experimenters concluded that these black fungi can survive in a Mars environment.[10]
Effects of micropores in salt pillars
In experimental studies of salt pillars in the Atacama desert, microbes are able to access liquid at extremely low relative humidities due to micropores in the salt structures. They do this through spontaneous capillary condensation, at relative humidities far lower than the deliquescence point of NaCl of 75%.[11]
![](https://upload.wikimedia.org/wikipedia/commons/thumb/8/8f/Salt_Pillars_-_Atacama_Desert.jpg/400px-Salt_Pillars_-_Atacama_Desert.jpg)
Micro-environmental data measured simultaneously outside and inside halite pinnacles in the Yungay region (table 2 from [13])
Variable | Halite exterior | Halite interior |
---|---|---|
Mean annual RH, % | 34.75 | 54.74 |
Maximum annual RH, % | 74.20 | 86.10 |
Minimum annual RH, % | 2.90 | 2.20 |
The researchers, Wierzchos et al., did detailed studies with scanning electron microscopes. At 75% relative humidity then brine was abundant inside the salt pillars. As the humidity was reduced, even at 30% RH, the cyanobacteria aggregates shrunk due to water loss, but still there were small pockets of brine in the salt pillars.[13]
"Endolithic communities inside halite pinnacles in the Atacama Desert take advantage of the moist conditions that are created by the halite substrate in the absence of rain, fog or dew. The tendency of the halite to condense and retain liquid water is enhanced by the presence of a nano-porous phase with a smooth surface skin, which covers large crystals and fills the larger pore spaces inside the pinnacles... Endolithic microbial communities were observed as intimately associated with this hypothetical nano-porous phase. While halite endoliths must still be adapted to stress conditions inside the pinnacles (i.e. low water activity due to high salinity), these observations show that hygroscopic salts such as halite become oasis for life in extremely dry environments, when all other survival strategies fail.
Our findings have implications for the habitability of extremely dry environments, as they suggest that salts with properties similar to halite could be the preferred habitat for life close to the dry limit on Earth and elsewhere. It is particularly tempting to speculate that the chloride-bearing evaporites recently identified on Mars may have been the last, and therefore most recently inhabited, substrate as this planet transitioned from relatively wet to extremely dry conditions"
Microbes also inhabit Gypsum deposits (CaSO4.2H2O), however Gypsum doesn't deliquesce. Researchers found that the regions of the desert that had microbial colonies within the gypsum correlated with regions with over 60% relative humidity for a significant part of the year. They also found that the microbes imbibed water whenever the humidity increased above 60% and gradually became desiccated when it was below that figure.[14]
References
- ↑ Surviving the conditions on Mars DLR, 26 April 2012
- ↑ de Vera, Jean-Pierre (2012). "Lichens as survivors in space and on Mars". Fungal Ecology. 5 (4): 472–479. doi:10.1016/j.funeco.2012.01.008.
- ↑ R. de la Torre Noetzel, F.J. Sanchez Inigo, E. Rabbow, G. Horneck, J. P. de Vera, L.G. Sancho Survival of lichens to simulated Mars conditions Archived 2013-06-03 at the Wayback Machine.
- ↑ Sánchez, F.J. (2012). "The resistance of the lichen Circinaria gyrosa (nom. provis.) towards simulated Mars conditions—a model test for the survival capacity of an eukaryotic extremophile". Planetary and Space Science. 72 (1): 102–110. Bibcode:2012P&SS...72..102S. doi:10.1016/j.pss.2012.08.005.
- ↑ Billi, Daniela; Viaggiu, Emanuela; Cockell, Charles S.; Rabbow, Elke; Horneck, Gerda; Onofri, Silvano (2011). "Damage Escape and Repair in DriedChroococcidiopsisspp. from Hot and Cold Deserts Exposed to Simulated Space and Martian Conditions". Astrobiology. 11 (1): 65–73. Bibcode:2011AsBio..11...65B. doi:10.1089/ast.2009.0430. ISSN 1531-1074. PMID 21294638.
- ↑ "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." Wynn-Williams, D.D.; Edwards, H.G.M.; Newton, E.M.; Holder, J.M. (2002). "Pigmentation as a survival strategy for ancient and modern photosynthetic microbes under high ultraviolet stress on planetary surfaces". International Journal of Astrobiology. 1: 39. Bibcode:2002IJAsB...1...39W. doi:10.1017/S1473550402001039.
- ↑ Brandt, Annette; de Vera, Jean-Pierre; Onofri, Silvano; Ott, Sieglinde (2014). "Viability of the lichen Xanthoria elegans and its symbionts after 18 months of space exposure and simulated Mars conditions on the ISS" (PDF). International Journal of Astrobiology. 14 (3): 1–15. Bibcode:2015IJAsB..14..411B. doi:10.1017/S1473550414000214. ISSN 1473-5504.
- ↑ de Vera, Jean-Pierre; Schulze-Makuch, Dirk; Khan, Afshin; Lorek, Andreas; Koncz, Alexander; Möhlmann, Diedrich; Spohn, Tilman (2014). "Adaptation of an Antarctic lichen to Martian niche conditions can occur within 34 days" (PDF). Planetary and Space Science. 98: 182–190. Bibcode:2014P&SS...98..182D. doi:10.1016/j.pss.2013.07.014. ISSN 0032-0633.
- ↑ de Vera, Jean-Pierre; Schulze-Makuch, Dirk; Khan, Afshin; Lorek, Andreas; Koncz, Alexander; Möhlmann, Diedrich; Spohn, Tilman (2014). "Adaptation of an Antarctic lichen to Martian niche conditions can occur within 34 days". Planetary and Space Science. 98: 182–190. Bibcode:2014P&SS...98..182D. doi:10.1016/j.pss.2013.07.014. ISSN 0032-0633.
This work strongly supports the interconnected notions (i) that terrestrial life most likely can adapt physiologically to live on Mars (hence justifying stringent measures to prevent human activities from contaminating / infecting Mars with terrestrial organisms); (ii) that in searching for extant life on Mars we should focus on "protected putative habitats"; and (ii) that early-originating (Noachian period) indigenous Martian life might still survive in such micro-niches despite Mars' cooling and drying during the last 4 billion years
- ↑ Zakharova, Kristina; Marzban, Gorji; de Vera, Jean-Pierre; Lorek, Andreas; Sterflinger, Katja (2014). "Protein patterns of black fungi under simulated Mars-like conditions". Scientific Reports. 4: 5114. Bibcode:2014NatSR...4E5114Z. doi:10.1038/srep05114. ISSN 2045-2322. PMC 4037706
. PMID 24870977.
The results achieved from our study led to the conclusion that black microcolonial fungi can survive in Mars environment.
- ↑ Bortman, Henry (Jul 25, 2011). "Islands of Life, Part V". Astrobiology Magazine (NASA).
- ↑ Davies, Paul (Aug 3, 2012). "The key to life on Mars may well be found in Chile". The Guardian.
- ↑ 13.0 13.1 Wierzchos, J.; Davila, A. F.; Sánchez-Almazo, I. M.; Hajnos, M.; Swieboda, R.; Ascaso, C. (2012). "Novel water source for endolithic life in the hyperarid core of the Atacama Desert" (PDF). Biogeosciences. 9 (6): 2275–2286. Bibcode:2012BGeo....9.2275W. doi:10.5194/bg-9-2275-2012. ISSN 1726-4189.
- ↑ Wierzchos, J.; Cámara, B.; De Los Ríos, A.; Davila, A. F.; Sánchez Almazo, I. M.; Artieda, O.; Wierzchos, K.; Gómez-Silva, B.; Mckay, C.; Ascaso, C. (2011). "Microbial colonization of Ca-sulfate crusts in the hyperarid core of the Atacama Desert: implications for the search for life on Mars" (PDF). Geobiology. 9 (1): 44–60. doi:10.1111/j.1472-4669.2010.00254.x. ISSN 1472-4677. PMID 20726901.
See also
This article may have some material from the 13:35, 25 May 2013 revision of Water on Mars on Wikipedia ( view authors). License under CC BY-SA 3.0| style="padding: 3px 10px;" | |