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Table of Contents INTRODUCTION............................................................................................................................................ 2 TYPES OF EXTREMOPHILES............................................................................................................................ 3 THERMOPHILES........................................................................................................................................................3 PSYCHROPHILES........................................................................................................................................................3 ACIDOPHILES........................................................................................................................................................4 ALKALIPHILES........................................................................................................................................................4 PIEZOPHILES.........................................................................................................................................................4 ENDOLITHS.......................................................................................................................................................... 4 XEROPHILES..........................................................................................................................................................5 RADIORESISTANTS..................................................................................................................................................5 POTENTIAL EXTRA-TERRESTRIAL LIFE............................................................................................................. 7 CONCLUSION.............................................................................................................................................. 11 REFERENCES............................................................................................................................................... 12

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4. Life in Extreme Conditions Introduction Extremophiles are known as organisms that are able to thrive under extreme conditions. This include, but not limited to, extreme high or low temperatures, highly acidic or basic environments, highly pressurized conditions, environments with high salt concentrations, extreme dry conditions, environments with poor nutritional content, or rocky environments (Niederberger, 2016). Certain extremophiles have the characteristics to survive multiple extremities in the environment, and they are called polyextremophiles. A large portion of extremophiles are microoganisms that produce enzymes which enable them to live in such extreme conditions (Berlemont & Gerday, 2011). They are mainly archaea, but can also come from the other major branches of life like bacteria and eukaryotes, containing multicellular organisms as well (Rampelotto, 2013). They equip us with the possible leads to understand the evolution of life on Earth during ancient times, due to the vastly different living conditions present then (Arora & Panosvan, 2019). This article aims to describe the types of extremophiles and their locations on Earth, as well as the possibility of their life in our Solar system.

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Types of extremophiles The types of extremophiles are mainly categorized according to the extreme living conditions they thrive in.

Thermophiles Thermophiles are organisms that thrive under high temperatures, and they are typically found in volcanic sites and hot springs (Arora & Panosvan, 2019). An example will be the bacteria Thermus Aquaticus, which thrives at temperatures around 70°C, and is found in the hotsprings of Yellowstone National Park in the US (Las Cumbres Observatory, 2020), within the Grand Prismatic Spring shown in Figure 1 (Janiskee, 2011).

Figure 1: Photo of Yellowstone Grand Prismatic Spring (Janiskee, 2011).

Psychrophiles Psychrophiles are organisms that grow in extreme cold, with different forms of characteristics and methods to adapt to such 3 Z5216045

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temperatures. One method will be the release of substances like glycerol to reduce the solidification point of water, avoiding the formation of ice crystals (Las Cumbres Observatory, 2020). Examples of such microbes are the gram-negative psychrophilic bacteria of Flavobacterium and Achromobacter, which could be found in the Arctic and Antarctic ocean (Rogers & Kadner, 2019).

Acidophiles Acidophiles are organisms that thrive in acidic environments, which includes sulfuric pools, acid mine drainage and the stomach of human bodies, as they are able to maintain their internal pH levels (Richlen, 2018). An example of them includes Acidiphilum Cryptum, which was found in the lake drained from a coal mine in Germany (Brett & Banfield, 2003).

Alkaliphiles Alkaliphiles are able to survive in extremely alkaline conditions. An example of them, the alkaliphilic bacteria, is able to develop active and passive regulatory processes in order to maintain internal pH levels (Bordenstein, 2020). They can be found in areas with high pH levels, including lakes like the Lake Calumet located southeast of Chicago, with bacterium from the Clostridium and Bacillus species (Astrobiology Magazine, 2003).

Piezophiles Piezophiles are organisms that survive under high pressure and can be found in deep sea hydrothermal vents. An example will be the archaeon Pyrococcus Yayanossi found in the Ashadze hydrothermal vent, which uses adaptations that alters its amino acid production and energy expenditure mechanisms (Michoud & Jebbar, 2016) to allow it to survive in such harsh conditions.

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Endoliths Endoliths grow within pores between minerals and thrive in rocky environments. They can be found in many places on Earth, including rocks on Earth’s crust and on the ocean beds, hence subdividing them to three broad categories: i.

Cryptoendoliths – Organisms that survive within the rocks on the Earth’s crust (Bruckner, 2020).

ii.

Subsurface endoliths – Organisms that survive underneath the Earth’s surface, within groundwater aquifers (Bruckner, 2020).

iii.

Deep-biosphere endpliths – Organisms that survive deep below the Earth’s ocean floor. They tend to be polyextremophiles too, due to the presence of high temperatures, the lack of oxygen content and the absence of sunlight conditions (Bruckner, 2020). An example will be microbes found in the South African gold mine (Schultz, 1999).

Xerophiles Xerophiles are organism that thrive in environments with low content of water. These environments include cryptobiotic soils in places like the Great Basin and Colorado Plateau, whereby microorganisms live in the fine crusts above soils that have the sacristy of water (Deiss, 2019). Another example will be organisms living in the Antarctic Dry Valleys, which have hardly any ice or water present, similar to the conditions of Mars, and allowing scientists to consider possible life in Mars (Astrobiology Magazine, 2002).

Radioresistants Radioresistants are extremophiles that are able to survive under living conditions with high levels of radiation. They can be found in various areas with such environmental conditions, including within the deep sea, with the example of the Exiguobacterium species that can be found in Andean lakes, and are resistant to Ultra-Violet B 5 Z5216045

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radiation (Singh and Gabani, 2011). Another example will be Deinococcus Radiodurans, as shown in Figure 2, which is claimed to be one of the organism that is the most radioresistant, and has been found in Antarctic dry valleys

Figure 2: Close up of Deinococcus Radiodurans (Murray, 2017)

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Potential extra-terrestrial Life Due to the presence of extreme living conditions outside of Earth, exploring the nature of extremophiles enable us to gain a deeper understanding on the potential extra-terrestrial life. Classifications among the habitability of planets have been proposed, and an example of it will be the four classes derived by Lammer et al. (2009): i.

Class I – Planets that have living conditions alike to Earth’s.

ii.

Class II – Planets with geophysical conditions similar to Venus or Mars.

iii.

Class III – Planets with potential water bodies present beneath the surface, and interacts with a core that contains high amounts of silicate.

iv.

Class IV – Planets with liquids and ice layers (Lamer et al., 2009)

These classifications can allow scientists to delve into deeper research on the growth of microorganisms, particularly extremophiles, living in this conditions that are present on other planetary habitats. In the recent years, experimentation was done to show whether certain microorganisms can survive under laboratory simulated environments of other planets. Research has shown promising results, including the ability of extremophiles to survive under harsh conditions similar to those in Mars and Enceladus (Schuerger & Nicholson, 2016), for example the microorganism Serratia Liquefacien (Fajardo-Cavazos et al., 2018). In order to determine what kind of conditions have the potential to life, we have to first identify the environmental conditions of extremophiles living in our own planet – under the categorisation of Class I planets (Merino et al., 2019). When we understand the environmental limitations of extremophiles in our own planet, scientists can then identify similar conditions in other planets that has the potential to support extraterrestrial life (Merino et al., 2019). 7 Z5216045

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By studying the planetary layers of Earth in comparison with other planets, scientists have been able to predict the presence of extremophiles outside of Earth. This was done by recording various parameters including temperature, pressure and salinity (Merino et al., 2019). This was tabulated in Table 1 below.

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Table 1: Geophysical conditions of planets (Merino et al., 2019)

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For example, planets like Titan and Europa has been found to have saline oceans with extremely low temperatures (Grindrod et al., 2008; Zolotov & Kargel, 2009). This is a good indicator that extremophiles, especially those in the psychrophile category may be present provided that they are able to survive the high pressure in these planets. Titan has a maximum pressure of 800 MPa (Sohl et al., 2014), while Europa has a maximum pressure of 30 MPa (Munoz-Iglesias, Bonales & Prieto-Ballesteros, 2013) . In comparison, the maximum pressure survived by Thermococcus piezophilus on Earth is 125MPa (Dalmasso et al., 2016), while experiments have shown that these organisms was found to be still active in up to pressures of 2000 MPa when put in specific environmental conditions like type-IV ice (Vanlint et al., 2011). Therefore, it is reasonable to conclude that there is a high possibility of extra-terrestrial life living in these planets, especially extremophiles that can survive both low temperatures and high pressures. Planets such as Europa has been found to contain high levels of radiation, with UV-C penetrating up to 20 cm into the surface of the planet. UV-C kills more than 99.9% of microorganisms (Nordheim, Hand & Paranicas, 2018). Therefore, for these extremophiles to exist on Europa, it is

necessary for them to: First, survive the extreme low temperatures (Merino et al., 2019). Secondly, withstand the high pressure of 30 MPa (Munoz-Iglesias et al., 2013). Finally, shielding from UV-C radiation by living more than 20 cm below the surface of Europa (Nordheim et al., 2018). Looking at the above, it is only in the consideration of 3 different parameters. In actual fact, the list of environmental parameters is inexhaustible. Therefore, it seems highly unlikely to find life on a planet such as Europa. In addition, the subsurface of planets might be a vital location to locate extra-terrestrial life, due to the presence of warmer temperatures , as showcased in Table 1 (Merino et al., 2019). On Mars, it has been shown that it has a higher subsurface temperature than the areas above it, and 10 Z5216045

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could potentially contain ground water (Clifford, Lasue, Heggy, Boisson, McGovern & Max, 2010). In addition, Mars could also occur serpentinization

in its subsurface, allowing the formation of hydrogen gas and organic chemistry compounds (Ehlmann, Mustard, & Murchie, 2010). As proven by the research by Sinha, Nepal, Kral, & Kumar (2017), this allows the growth of Methanothermobacter wolfeii, that survives Martian conditions of 55 °C and a pressure between 0.1-122 MPa. As such, this shows the possibility of extremophiles living on other planets, due to their ability to survive in such extreme conditions that could be present in outer space. In addition, scientists have synthesized extremophilic microbials that could survive in space, in order to speculate the possibility of their presence. An example will be Tardigrades, shown in Figure 3 below, also known as water bears, could survive in the vacuum environment out of space, due to its foreign DNA (Hall, 2015). This prompts scientists to further explore the living adaptations of extremophiles in order to possibly find living things out of Earth.

Figure 3: Close up of a Tardigrade (Hall, 2015)

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Conclusion In conclusion, the study of extremophiles can provide scientists with a deeper understanding towards the evolution of life on Earth, as well as the possibility of extra-terrestrial life, due to their ability to survive in such extreme living conditions. With the wide range of organisms living on Earth, it gives researchers an insight of potential source of alternative energy that could be present elsewhere in space, that might bring about living organisms. Just like the water bears that survived in space (Space.com, 2008), it is predicted that in the next couple of years, more self-reproducing lab-produced microbes will be synthesized, providing scientists with much more information about life in outer space (Borthwick, 2015). (1800 words)

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References Arora, N.K. & Panosyan, H. (2019). Extremophiles: applications and roles in environmental sustainability. Environmental Sustainability 2, 217–218 https://doi.org/10.1007/s42398-019-00082-0 Astrobiology Magazine. (2002). Antarctic microbes colonize under Mars-like conditions. Extreme life. Retrieved from: https://www.astrobio.net/extreme-life/antarctic-microbes-colonize-undermars-like-conditions/ Astrobiology Magazine. (2003). Superbug survival is basic. Extreme life. Retrieved from: https://www.astrobio.net/extreme-life/superbug-survivalis-basic/ Berlemont, R. & Gerday, C. (2011). Extremophiles. In Comprehensive Biotechnology, 229–242. https://doi.org/10.1016/B978-0-08-0885049.00030-1 Bordenstein, S. (2020). Microbial Life in Alkaline Environments. Microbial Life Educational Resources. Retrieved from: https://serc.carleton.edu/microbelife/extreme/alkaline/index.html Borthwick, L. (2015). The Hunt for Alien Extremophiles is Taking Off (Kavli Q+A). Space.com. Retrieved from: https://www.space.com/28414-hunt-foralien-extremeophiles.html Brett, J. B. & Banfield, J. F. (2003). Microbial communities in acid mine drainage, FEMS Microbiology Ecology 44(2), 139-152. https://doi.org/10.1016/S0168-6496(03)00028-X Bruckner, M. (2020). Endoliths—Microbes Living within Rocks. Microbial Life Educational Resources. Retrieved from: https://serc.carleton.edu/microbelife/extreme/endoliths/index.html Clifford, S. M., Lasue, J., Heggy, E., Boisson, J., McGovern, P., & Max, M. D. (2010). Depth of the Martian cryosphere: Revised estimates and implications for the existence and detection of subpermafrost groundwater. Journal of Geophysical Research: Planets, 115(E7). https://doi.org/10.1029/2009JE003462 Dalmasso, C., Oger, P., Selva, G., Courtine, D., L’haridon, S., Garlaschelli, A., ... & Takai, K. (2016). Thermococcus piezophilus sp. nov., a novel 13 Z5216045

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hyperthermophilic and piezophilic archaeon with a broad pressure range for growth, isolated from a deepest hydrothermal vent at the Mid-Cayman Rise. Systematic and applied microbiology, 39(7), 440-444. https://doi.org/10.1016/j.syapm.2016.08.003 Diess, J. (2019). Microbial Life in Environments Without Water. Educational Resources. Retrieved from: https://serc.carleton.edu/microbelife/extreme/withoutwater/index.html Ehlmann, B. L., Mustard, J. F., & Murchie, S. L. (2010). Geologic setting of serpentine deposits on Mars. Geophysical research letters, 37(6). https://doi.org/10.1029/2010GL042596 Fajardo-Cavazos, P., Morrison, M. D., Miller, K. M., Schuerger, A. C., and Nicholson, W. L. (2018). Transcriptomic responses of Serratia liquefaciens cells grown under simulated Martian conditions of low temperature, low pressure, and CO2-enriched anoxic atmosphere. Sci. Rep 8(14938). https://doi.org/10.1038/s41598-018-33140-4 Grindrod, P. M., Fortes, A. D., Nimmo, F., Feltham, D. L., Brodholt, J. P., and Voèadlo, L. (2008). The long-term stability of a possible aqueous ammonium sulfate ocean inside Titan. Icarus 197, 137–151. https://doi.org/10.1016/j.icarus.2008.04.006 Hall, J. (2015). Tardigrades, already impossible to kill, also have foreign DNA. ExtremeTech. Retrieved from: https://www.extremetech.com/extreme/218492-tardigrades-alreadyimpossible-to-kill-also-have-foreign-dna Janiskee, B. (2011) Thermophile Research in Yellowstone Helps Guide the Search for Extraterrestrial Life. National Parks Traveler. Retrieved from: https://www.nationalparkstraveler.org/2011/01/thermophile-researchyellowstone-helps-guide-search-extraterrestrial-life7446 Lammer, H., Bredehöft, J.H., Coustenis, A. et al. (2009). What makes a planet habitable? Astron Astrophys Rev 17, 181–249. https://doi.org/10.1007/s00159-009-0019-z Langeley, L. (2013). 5 Extreme Life-Forms That Live on the Edge. NATIONAL GEOGRAPHIC SOCIETY NEWSROOM. Retrieved from: https://blog.nationalgeographic.org/2013/08/02/5-extreme-life-forms-thatlive-on-the-edge/

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