• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

How had research over the past 25 years led us to think that microbes may be able to survive in extraterrestrial environments?

Free essay example:

APS 325 Life in Extreme Environments                050139246

Our current understanding of life in extreme environments strongly suggests that if life exists elsewhere in the solar system it is highly likely to be microbial.  How has research over the past 25 years led us to think that microbes may be able to survive in such extraterrestrial environments?

The idea of extraterrestrial life is not novel. Over 2,000 years ago, a Greek philosopher wrote, "It is unnatural in a large field to have only one shaft of wheat, and in the infinite Universe only one living world" (Papagiannis 1984). Enthusiasm concerning life elsewhere in the solar system continued towards the late 20th century (Brake 2006), until these ancient old notions were dashed when robotic space explorations revealed inhospitable planets (Klein 1999).  

Nonetheless, more recently, discoveries closer to home revived interest in the possibility of extraterrestrial life.  Over the last few decades, not only have many environmental extremes on Earth been uncovered, but organisms have been found thriving in these conditions(Rothschild & Mancinelli 2001).  These organisms were named extremophiles (‘lovers of extreme’ Malceroy 1974).  The term ‘extreme’ is difficult to define since it is dependent on the organism; ‘extreme’ for one organism might be the norm, or even essential, to the survival of another.  However, a scientifically viable definition of ‘extreme’ that will be used for the purpose of this essay is conditions which are detrimental to most organisms.

Space explorations have revealed other planets with environmental extremes analogous to those found on earth. Therefore the discovery of extremophiles has made the search for extraterrestrial life more plausible. Furthermore, as more extremophiles are uncovered in what previously were thought to be uninhabitable environments, our view of the conditions required for life becomes less restricted.

Extremophiles are found in all domains of life; from radiation-resistant bacteria (Anderson et al 1956) to extreme sunflowers thriving in salt marshes (Rieseberg et al 2003).  However, research over the past 25 years has shown that microbes are the most abundant group of extremophiles (Satyanarayana et al 2005). It is therefore logical to assume that if extraterrestrial life exists, it is highly likely to be microbial.  This essay examines the study of microbial extremophiles and its implication for life elsewhere in the solar system, using examples [see Table 1].image00.png

Thermophiles are extremophiles adapted for life in intensely hot environments, approximately in excess of 40°C, such as hot springs and deep-water hydrothermal vents (Brock 1986).  Temperatures at these locations would prove fatal to most organisms because biomolecules, including enzymes and nucleic acids, begin to deteriorate at high heat (Somero 1995).  Furthermore, high temperatures fatally increase the fluidity of membranes.    However, research over the past 25 years has shown that thermophiles have evolved adaptations in order to thrive in extreme hot environments where most organisms would perish.  

Thermophile membranes largely contain saturated lipids which increase integrity, making it more resistant to heat (McElhaney 1976).  Furthermore, thermophile DNA is stable at high temperatures due to high salt concentrations (Marguet & Forterre 1998).  In addition their DNA has gyrases (loops) that form super coils.  Consequently, thermophile DNA is tightly coiled, preventing it from damage in high temperatures (Forterre et al 1995).  Also, thermophiles have heat-resistant enzymes (Adams et al 1995).  These enzymes are able to retain their structure in high temperatures, and therefore remain operational in conditions where other enzymes would denature.  For example, a unique variant of DNA polymerase enzyme is essential for the survival of the bacterium Thermus aquaticus, discovered in hot springs at Yellowstone National Park (Brock & Freeze 1969). DNA polymerase is commonly used by organisms to assist DNA replication, and conventionally denatures at high heat.  In contrast, the variant used by T.aquaticus, named Taq polymerase, functions optimally at 75-80°C. Taq polymerase was isolated from T.aquaticus and is now one of the most significant enzymes in molecular biology.  It is an essential part of the polymerase chain reaction (PCR) technique used to amplify DNA sequences (Saiki 1988).

At high temperatures, chlorophyll is degraded and therefore photosynthetic organisms cannot exist (Rothschild & Mancinelli 2001).  Consequently, another problem facing thermophiles is finding an alternative source of nutrition.  For example, Pyrolobus fumarii is a microbe that grows on the walls of deep-sea hydrothermal vents and can propagate in temperatures up to 113°C(Blöchl et al 1997). (P.fumarii was previously the most extreme thermophile known until the discovery of ‘Strain 121’(Kashefi & Lovley 2003), which increased the upper temperature limit for life to 121°C). P.fumarii is a chemoautotroph and synthesises its own food from surrounding chemicals, such as hydrogen.  

The existence of thermophiles has significant implications for the possibility of life elsewhere in the solar system.  It expands the prospect that life can exist in extremely hot extraterrestrial environments, such as those predicted on Jupiter’s moon, Io.  This satellite is heated by tidal activities from Jupiter and possesses numerous active volcanoes on its surface (Lopes et al 2004).  Also, findings of chemoautotrophs have dashed the ideas that energy from the Sun is a requirement for life.  It is now known that communities, such as those found at deep-sea hydrothermal vents, can thrive by exclusively using inorganic compounds as energy sources (Lutz & Kennish 1993). This opens the mind to the possibility that life may exist in the sub-surface of planets elsewhere in the solar system (Schulze-Makuch & Irwin 2001, Pirajno & Van Kranendonk 2005).

Psychrophiles are organisms that exist in extreme cold environments.  These extremophiles have an optimal growth at approximately 15°C or lower (Morita 1975).  Such temperatures are detrimental to most organisms because membranes lose integrity and enzyme activity decreases (Somero 1995).  Furthermore, the formation of ice crystals can cause severe structural cell damage.  However, research over the past 25 years has shown that psychrophiles are well-adapted to their cool environments.  

Psychrophile membranes are made largely from unsaturated lipids which enhance membrane fluidity at low temperatures (Russell 1997).  Also, they have enzymes adapted to operate at near freezing temperatures (Gerday et al 2000).  For example Polaromonas vacuolata, found in Antarctic sea ice, optimally multiplies at temperatures of 4°C (Irgens et al 1996).  However, above 12°C it will cease to reproduce because its enzymes have adapted to function over a lower temperature range.  To prevent ice crystal damage, some psychrophiles produce cyroprotectants (such as glycerol), which effectively lower a cell’s freezing point, allowing it to maintain flexibility in low temperatures (Krembs et al 2002).  

Contrary to thermophiles, photosynthetic psychrophiles, such as Chlamydomonas nivalis (also known as ‘red snow’ due to the colouration it creates), are able to photosynthesise at near to freezing temperatures (Williams et al 2003).  This provides extremophile communities with a possible energy source in extremely cold environments.  

Recently there have been discoveries of lakes (kept liquid by pressure) under the ice sheet of Antartica, and it is speculated that extremophiles may exist in these hidden waters (Gavaghan 2002).  This would have significant implications for extraterrestrial life since conditions predicted for these lakes may be similar to those believed to be present underneath the ice crust of Europa, another of Jupiter’s moons (Kargel et al 2000).  Using these Earth lakes, life detection techniques could be refined before venturing into the solar system, hence increasing the success of extraterrestrial life searches.

Halophiles are extremophiles that thrive in salty environments, such as salt lakes, salterns and the Dead Sea.  At these locations organisms become very dehydrated as they lose water through their cell walls by osmosis (Rothschild & Mancinelli 2001). However, research over the past 25 years has revealed how halophiles avoid this fate.  Halophilic algae, such as Dunaliella salina, and bacteria balance the external osmotic pressure by producing compatible solutes such as glycerol (Galinski 1993).  Halobacterium (Archaea) achieve the same effect using a molecular pump to exclude sodium ions from the cell, whilst accumulating potassium ions within the cell (Speelmans et al 1995).

Discoveries of halophiles are important in the search for life elsewhere, particularly concerning the Meridiani Planum plains of Mars.  After discoveries of evaporates containing high sodium chloride concentrations, these plains are a hypothesised previous salt lake, perhaps once home to halophiles (Litchfield 1998).

Piezophiles are organisms that thrive under great pressure.  Pressure is problematic to life as it compresses biomolecules to fatal levels (Mozhaev et al 1996).  However, research over the last 25 years has discovered that piezophiles are adapted to tolerate these effects.  For example, piezophile membranes are largely made from unsaturated lipids which help circumvent problems caused by high pressure (Yano et al 1998).  Also a study by Sharma et al (2002) showed that even bacteria not adapted to high-pressure, such as Escherichia coli, can tolerate pressures equivalent to those experienced at 160km under water.

Piezophiles (and pressure tolerant bacteria) are important in the search for extraterrestrial life as it allows for the possibility of organisms thriving in high-pressure conditions elsewhere in the solar system such as the sub-surface of planets.  Therefore, although space missions have detected no life on the surface of planets (Klein 1999), there is a possibility for the existence of sub-surface organisms.  

To conclude, until relatively recently there has been limited knowledge regarding Earth’s extreme environments.  As our exploration continues we realise our view as to what forms of life might take is constrained.  Nevertheless, before venturing out into the unknown to discover extraterrestrial life, it would perhaps be wise to continue studying these exotic areas closer to home.  Extremophiles provide us with a template for life on other planets, and encourage us to broaden our perspective of where life may exist.   With an expanded idea of the necessities for life, coupled with further study of extremophiles, improvements in exploration and analytical technology can be made; effectively arming ourselves with the tools required for a successful extraterrestrial life search.  By opening our minds to novel possibilities and refining our expertise, we may soon find life elsewhere in the solar system, as predicted long ago by our ancient predecessors.

References:

Adams, M.W.W., Perler, F.B. & Kelly, R.M. (1995)Extremozymes: Expanding the Limits of Biocatalysis. Nature Biotechnology, 13, 662 – 668.

Anderson, A.W., Nordon, H.C., Cain, R.F., Parrish, G. & Duggan, D. (1956) Studies on a radio-resistant micrococcus. I. Isolation, morphology, cultural characteristics, and resistance to gamma radiation. Food Technology, 10, 575-578.

Blöchl, E., Rachel, R., Burggraf, S., Hafenbradl, D., Jannasch, H.W. & Stetter, K.O.  (1997) Pyrolobus fumarii , gen. and sp. nov., represents a novel group of archaea, extending the upper temperature limit for life to 113°C. Extremophiles, 1, 14-21.

Brake, M. (2006) On the plurality of inhabited worlds: a brief history of extraterrestrialism. International Journal of Astrobiology, 5, 99-107.

Brock, T.D. & Freeze, H.  (1969) Thermus aquaticus, gen. and sp. nov., a Nonsporulating Extreme Thermophile.  Journal of Bacteriology, 98, 289–297.

Brock, T.D. (1986) General, Molecular and Applied Microbiology. Wiley, New York.

Galinski, E. A. 1993. Compatible solutes of halophilic eubacteria: molecular principles, water-solute interactions, stress protection. Experientia49: 487-496..

Gavaghan, H.  (2002)  Life in the Deep Freeze. Nature, 415, 828-830.

Gerday, C., Aittaleb, M., Bentahir, M., Chessa, J.P., Claverie, P., Collins, T., D’Amico, S., Dumont, J., Garsoux, G., Georlette, D., Hoyoux, A., Lonhienne, T., Meuwis, M.A. & Feller, G. (2000). Cold-adapted enzymes: from fundamentals to biotechnology. Trends in Biotechnology, 18, 103-107.

Forterre, P., Confalonieri, F., Charbonnier, F. & Duguet, M. (1995). Speculations on the origin of life and thermophily - review of available information on reverse gyrase suggests that hyperthermophilic prokaryotes are not so primitive. Origins of Life and Evolution of the Biosphere25, 235-249.

Irgens, R.L., Gosink, J.J. & Staley, J.T.  (1996) Polaromonas vacuolata gen. nov., sp. nov., a Psychrophilic, Marine, Gas Vacuolate Bacterium from Antarctica.  International Journal of Systematic Bacteriology, 46, 822-826.

Kargel, J.S., Kaye, J.Z., Head, J.W., Marion, G.M., Sassen, R., Crowley, J.K., Ballesteros, O.P., Grant, S.A. & Hogenboom, D.L. (2000) Europa's Crust and Ocean: Origin, Composition, and the Prospects for Life. Icarus, 148, 226 -265.

Kashefi, K. & Lovley, D.R. (2003) Extending the Upper Temperature Limit for Life.  Science, 301, 934.

Klein, H.P. (1999) Did Viking Discover Life on Mars? Origins of Life and Evolution of Biospheres,29, 625-631.

Krembs, C., Eicken, H., Junge, K., and Deming, J.W. (2002) High concentrations of exopolymeric substances in Arctic winter sea ice: implications for the polar ocean carbon cycle and cryoprotection of diatoms. Deep Sea Research, 49, 2163–2181.

Litchfield, C. D. (1998) Surrvival Strategies for Microorganisms:Hypersaline Environments and Their Relevance to Life on Early Mars. Meteoritics and Planetary Science, 33, 813-819.

Lopes, R.M.C, Kamp, L.W., Smythe, W.D., Mouginis-Mark, P., Kargel, J., Radebaugh, J., Turtle, E.P., Perry, J., Williams, D.A., Carlson, R.W., Douté, S. & the Galileo NIMS and SSI Teams (2004) Lava Lakes on Io: Observations of Io's Volcanic Activity from Galileo NIMS During the 2001 Fly-bys. Icarus, 169, 140–174. 

Lutz R.A. & M.J. Kennish. (1993) Ecology of Deep-Sea Hydrothermal Vent Communities: a Review. Reviews of Geophysics, 31, 241-242.

Macelroy, R.D.  (1974) Some comments on the evolution of extremophiles. Biosystems,6, 74–75.

Marguet, E. & Forterre, P. (1998) Protection of DNA by salts against thermodegradation at temperatures typical for hyperthermophiles. Extremophiles,2, 115–122.

McElhaney, R.N. (1976) The biological significance of alterations in the fatty acid composition of microbial membrane lipids in response to changes in environmental temperature. In Extreme Environments: Mechanisms of Microbial Adaptation, Academic Press, New York, 255-281.

Morita, RY. (1975) Psychrophilic bacteria. Bacteriological Review, 39, 144-167.

Mozhaev, V.V., Heremans, H., Frank, J., Masson, P., Balny, C.  (1996)High pressure effects on protein structure and function. Proteins Structure Function and Genetics, 24, 81-91.

Papagiannis, M.D.  (1984) A historical introduction to the search for extraterrestrial life - The search for extraterrestrial life: Recent developments.  Proceedings of the Symposium, June, 18-21.

Pirajno, F. & Van Kranendonk, M.J. (2005) Review of hydrothermal processes and systems on Earth and implications for Martian analogues.  Australian Journal of Earth Sciences, 52, 329-351.

Rieseberg, L.H., Raymond, O., Rosenthal, D.M., Lai, Z., Livingstone, K., Nakazato, T., Durphy, J.L., Schwarzbach, A.E., Donovan, L.A. & Lexer, C.  (2003) Major ecological transitions in wild sunflowers facilitated by hybridization. Science, 301, 1211-1216.

Rothschild, L.J. & Mancinelli, R.L.  (2001) Life in extreme environments. Nature, 409, 1092-1101.

Russell, N.J. (1997) Psychrophilic bacteria—Molecular adaptations of membrane lipids.  Comparative biochemistry and physiology A, 118, 489-493.

Saiki, R.K., Gelfand, D.H., Stoffel, S., Scharf, S.J., Higuchi, R., Horn, G.T., Mullis, K.B., Erlich, H.A. (1988) Primer-directed enzymatic amplification of DNA with a thermostable DNA polymerase. Science, 239, 487–91.        

Satyanarayana1,T., Raghukumar, C. & Shivaji, S.  (2005) Extremophilic microbes: Diversity and perspectives. Current science, 89, 78-90.

Schulze-Makuch, D. & Irwin, L.N. (2001) Alternative Energy Sources Could Support Life on Europa. Transactions American Geophysical Union, 82, 150-153.

Sharma, A., Scott, J.H., Cody, G.D., Fogel, M.L., Hazen, R.M., Hemley, R.J. & Huntress, W.T. (2002) Microbial Activity at Gigapascal Pressures. Science, 295, 1514-1516.

Somero, G.N. (1995) Proteins and temperature.  Annual Review of Physiology, 57, 43-68.

Speelmans, G., Poolman, B. & Konings, W.N. (1995) Na+ as coupling ion in energy transduction in extremophilic Bacteria and Archaea. World Journal of Microbiology and Biotechnology, 11, 58-70.

Williams, W.E., Gorton, H.L. & Vogelmann, T.C. (2003). Surface gas-exchange processes of snow algae. Proceedings of the National Academy of Sciences, 100, 562–566.

Yano, Y., Nakayama, A., Ishihara, K. & Saito, H. (1998) Adaptive Changes in Membrane Lipids of Barophilic Bacteria in Response to Changes in Growth Pressure. Applied and Environmental Microbiology, 64, 479-485.

This student written piece of work is one of many that can be found in our University Degree Microbiology section.

(?)
Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Related University Degree Biological Sciences Skills and Knowledge Essays

See our best essays

Related University Degree Microbiology essays

  1. LITERATURE REVIEW THE BIODEGRADABILITY OF STARCH-BASED PLASTICS

    running water must be excluded to determine that the decomposition is due to biodegradation and not other causes (Arevalo-Nino, K 1996). The main objective in the degradation of plastics, regardless of its base material, is to break the long polymer chains allowing the embrittlement and subsequent fragmentation of the polymers by natural forces.

  2. A pathophysiology review on emphysema

    However a study in Japan done by Wang et al. did find a correlation between cigarette smoking and the severity of emphysema as did Gilloly and Lamb. The variations in results may have been due to the differences in the participants that was used in the study and also since

  1. Free essay

    Identifying microorganisms using differential staining techniques

    so when the culture is stained, gram positive bacteria will be noticeable and have that purple colour. If an older culture is used it has the possibility to turn from gram positive to gram negative and when this happens the results of the gram test are not differentiable because now

  2. Investigation into the effect of Temperature on the action of the Enzyme Lipase.

    tube holding the mixture in the appropriate water bath and start the timer. 7. Using a test tube of milk as a control check when the mixture changes to the same colour as the milk. Stop the timer and record the time taken for the reaction to occur.

  1. Bacterial Metabolism and Enzymatic Growth

    The three species of bacteria, previously mentioned, were spotted onto three different agar mediums, starch, tween 80, and milk and incubated for 48-72 hours at 37�C. If, on the starch agar, there was a clearing around the bacterial colony, the bacterium is one which hydrolyzes starch.

  2. Identification of an Unknown Enterobacteriaceae. The purpose of the experimental determination of an unknown ...

    If urease is produce, then the pH indicator (phenol red) in the medium detects the alkaline condition from ammonia production and turns the medium bright pink indicating positive result. (Alachi, P. 2007) Phenylalanine deaminase is an enzyme that degrades amino acid phenylalanine into phenylpyruvic acid which can be detected by adding ferric chloride.

  1. Antigen-Antibody Interactions: an analysis

    Vincent et al., 1970 reports a lag period being evident when the reaction proceeds slowly as is the case during the antigen excess zone, however no such observation is made presently. This apparent discrepancy is attributable to an increased concentration of reactants employed here.

  2. Distinguishing Species of Bacteria

    coli + - Bacillus subtilis + - Pseudomonas aeruginosa + + The table above shows that the ideal results are the same as the results from table 11. Discussion According to Table , Escherichia coli and Proteus vulgaris showed fermentative activity.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work