Life at the Limits. Organisms in Extreme Environments

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In the case of low temperatures, the temperature at which metabolism ceases may not represent the point at which the organism dies. There are important differences between the lethal effects of high and low temperatures. The damage caused by high temperature is destructive as proteins become denatured and other irreversible changes occur. The effect of low temperature may be rather different. As the temperature falls, metabolism slows and if the temperature is low enough, it ceases as the kinetic energy imparted to chemical reac- 2 life at the limits tions decreases.

This effect is potentially reversible. Death may result, however, from events such as irreversible changes in membrane func- tion, although freezing, or the risk of freezing, is likely to be the major hazard. Freezing involves a change in the state of water within the organism from a liquid to a solid. This can be a sudden and violent event, and initiates a number of changes that may result in death, unless the organism has mechanisms which enable it to survive the stresses involved.

The lethal effects of heat are unlikely to be due to a introduction: extreme life 3 D eath H eat com a O ptim um D eath? At low temperatures, metabolism is undetectable. As the temperature increases, the rate of metabolism increases due to the increased kinetic energy supplied to reactions.


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Beyond the optimum temperature, however, metabolism slows and eventually ceases due to the damaging and lethal effects of high temperature. Changes in activity are associated with these changes in temperature. As the temperature increases or decreases from the optimum, the organism may become disorientated and normal processes disrupted heat or cold stupor and then cease altogether heat or cold coma. In space there is cosmic and galactic radiation to contend with as well. The dangers of UV and ionizing radiation range from inhibition of photosynthesis up to damage to nucleic acids.

Direct damage to DNA or indirect damage through the production of reactive oxygen molecules can alter the sequence or even break DNA strands. Several bacteria including two Rubrobacter species and the green alga Dunaliella bardawil , can endure high levels of radiation. Deinococcus radiodurans , on the other hand, is a champ and can withstand up to 20 kGy of gamma radiation and up to 1, joules per square meter of UV radiation.

Indeed, D. This extraordinary tolerance is accomplished through a unique repair mechanism which involves reassembling damaged fragmented DNA. Scientists at the Department of Energy are looking to augment the D. So eager are biotechnologists to understand just how D.

Life at the Limits: Organisms in Extreme Environments

Gravity is a constant force in our lives; who has not imagined what it would be like to be an astronaut escaping gravity even temporarily? Gravitational effects are more pronounced as the mass of an organism increases. That being said, flight experiments have revealed that even individual cells respond to changes in gravity. Cell cultures carried aboard various spacecraft including kidney cells and white blood cells showed marked alterations in their behavior, some of which is directly due to the absence of the effects of a strong gravity field.

Indeed, recent work conducted aboard Space Shuttle missions has shown that there is a genetic component as yet understood to kidney cell responses to microgravity exposure. Pressure increases with depth, be it in a water column or in rock. Hydrostatic water pressure increases at a rate of about one-tenth of an atmosphere per meter depth, whereas lithostatic rock pressure increases at about twice that rate. Pressure decreases with altitude, so that by 10 km above sea level atmospheric pressure is almost a quarter of that at sea level.

It has also yielded obligately piezophilic species i. A bit of creative thinking suggests other physical and chemical extremes not considered here, including unusual atmospheric compositions, redox potential, toxic or xenobiotic manmade compounds, and heavy metal concentration. There are even organisms such as Geobacter metallireducens that can survive immersion in high levels of organic solvents such as those found in toxic waste dumps. Others thrive inside the cooling water within nuclear reactors.

While these organisms have received relatively little attention from the extremophile community, the search for life elsewhere may well rely on a better understanding of these extremes. The study of extremophiles holds far more than Guinness Book of World Records-like fascination. Seemingly bizarre organisms are central to our understanding of where life may exist and where our own terrestrial life may one day travel.

Did life on Earth originate in a hydrothermal vent? Will extremophiles be the pioneers that make Mars habitable for our own more parochial species? A deep ocean hydrothermal vent belching sulfide-rich hot water. A variety of life forms comprise a food web based on bacteria that live off of the energy provided by the sulfide-rich vent waters. Happily, extremophile research has a lucrative side. Industrial processes and laboratory experiments may be far more efficient at extremes of temperature, salinity and pH, and so on.

Natural products made in response to high levels of radiation or salt have been sold commercially. Glory too goes to those working with extremophiles. At least one Nobel Prize, that for the invention of the polymerase chain reaction PCR , would not have been possible without an enzyme from a thermophile. As the world of molecular biology has become increasingly reliant on products from extremophiles, they will continue be the silent partner in future awards.

Current work on extremophiles in space focuses on four major environments: manned-flight vehicles, interplanetary space because of the potential for panspermia , Mars and Europa because of the possibility of liquid water — and thus life. Mars is, at first blush, inhospitable. Temperatures are, for the most part, frigid, exposure to ultraviolet radiation is high, and the surface is highly oxidizing, precluding the presence of organic compounds on the surface. Yet hydrogeological evidence from Mars Global Surveyor hints that liquid water may even flow today under the surface.

Previous evidence seems to show that it once flowed much more freely on the surface in ancient times. Could Mars harbor subsurface life, similar to the subsurface or hydrothermal communities found on Earth? If so, it would be protected from surface radiation, damaging oxidants, and have access to liquid water.

Mars is rich in carbon dioxide, the raw material used by plants to produce organic carbon.


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This Mars Global Surveyor spacecraft photo shows gullies eroded into the wall of a meteor impact crater in Noachis Terra. It is possible that these gullies indicate that liquid water is present within the Martian subsurface today. With evidence mounting that one or more of the large moons of Jupiter Europa, Ganymede, Callisto have ice-covered oceans, the possibility of life on these moons becomes a subject of scientific discourse.

One of these, Europa, has an ice layer too thick to allow enough light to get through to allow photosynthesis, the process that drives much of terrestrial life including those under the perennially ice-covered lakes of Antarctica. The Galileo spacecraft has detected a weak magnetic field on Callisto, suggesting that salt water may lie beneath an ice-covered surface.

Supportive evidence exists as well for an ocean with Ganymede.

Space is extremely cold, subject to unfiltered solar radiation, solar wind, galactic radiation, space vacuum, and to negligible gravity. But this treacherous realm can be crossed by life. We know from Mars meteorites such as the now famous ALH sample that a natural vehicle exists for interplanetary transport.

Life in Extreme Environments: A PLOS Cross-Journal Call for Papers

These meteorites contain organic compounds from Mars, showing that such compounds can survive the journey. The criticism that life cannot endure extended periods in space is now being tested experimentally in space simulation facilities in the U. Survivors to date include spores of Bacillus subtilis and halophiles in the active vegetative state. Indeed, by studying the extremophiles here on Earth, we may get the first clear indication of what ET could be like — or at least the range of things they might eat and breathe. Norton, C. Survival of halobacteria within fluid inclusions in salt crystals.

Rothschild, L. Metabolic activity of microorganisms in gypsum-halite crusts. Vreeland, R. Nature , Macelroy, R. Some comments on the evolution of extremophiles. Since some of these acidophiles are closely related to cultured neutrophiles, we can conclude that eukaryotes must have the ability to adapt from neutral to acidic environments over relatively short periods of time. Thus, eukaryotic extremophiles are more widely distributed and phylogenetically diverse than previously thought. National Center for Biotechnology Information , U. Journal List Life Basel v.

8 Creatures That Can Survive the Most Extreme Conditions

Life Basel. Published online Jul 4. Angeles Aguilera. Author information Article notes Copyright and License information Disclaimer. This article has been cited by other articles in PMC. Abstract A major issue in microbial ecology is to identify the limits of life for growth and survival, and to understand the molecular mechanisms that define these limits. Introduction Our ongoing exploration of Earth has led to continued discoveries of life in environments that have been previously considered uninhabitable. Eukaryotic Extremophiles When we think of extremophiles, prokaryotes come to mind first.

Acidic Environments. Open in a separate window. Figure 1. Figure 2. Photosynthesis in Acidic Environments Photosynthesis is known to be particularly sensitive to stressful environmental conditions, such as salinity, pH or presence of toxicants. Figure 3. Conclusions Extremophiles are not only important resources for developing novel biotechnological processes, but also ideal models for research in the ecological and molecular fields.

Conflicts of Interest The author declares no conflict of interest. References 1. Microbial ecology of an extreme acidic environment, the Tinto River. Pikuta E. Microbial extremophiles at the limits of life.

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Brock T. Thermophilic Microorganisms and Life at High Temperatures. Springer-Verlag; Berlin, Germany: Roberts D. Eukaryotic Cells under Extreme Conditions. In: Seckbach J. Enigmatic Microorganisms and Life in Extreme Environments. Caron D. The growing contributions of molecular biology and immunology to protistan ecology: Molecular signatures as ecological tools. Alexandrof V. Cells, Molecules and Temperature.

Conformational Flexibility of Macromolecules and Ecological Adaptations; p. Rothschild L. Life in extreme environments. Lower pH limit for the existence of blue-green algae: Evolutionary and ecological implications. Seckbach J. Developments in Hydrobiology. Kluwer Academic Publication; Dordrecht, Germany: Ciniglia C.

Life at the limits : organisms in extreme environments in SearchWorks catalog

Hidden biodiversity of the extremophilic Cyanidiales red algae. Stibal M. Seasonal and diel changes in photosynthetic activity of the snow alga Chlamydomonas nivalis Chlorophyceae from Svalbard determined by pulse amplitude modulation fluorometry. FEMS Microbiol. Garrison D. Winter ecology of the sea ice biota in Weddel Sea pack ice. Gross S. Acidophilic and acid-tolerant fungi and yeasts. Russo G. Oggerin M. Schleper C. Life at extremely low pH. Baffico G. Nordstrom D. Geomicrobiology of Sulphide Mineral Oxidation. In: Banfield J. Geomicrobiology: Interactions Between Microbes and Minerals.

Volume Johnson D. Biodiversity and ecology of acidophilic microorganisms. Amaral L. Aguilera A. Boulter C. Did both extensional tectonics and magmas act as major drivers of convection cells during the formation of the Iberian Pyritic Belt massive sulfide deposits? Leistel J. The volcanic-hosted massive sulphidic deposits of the Iberian Pyritic Belt. A molecular approach to the characterization of the eukaryotic communities of an extreme acidic environment: Methods for DNA extraction and denaturing gradient electrophoresis analysis. Visviki I. DeNicola D.

A review of diatoms found in highly acidic environments.