4.Life the only living organisms that were able

4.Life in Extreme
Conditions

 

Introduction

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The Early Earth had an environment with severe conditions with
surface temperatures of 70-80 degrees Celsius, low pH levels, little 02
in the surrounding atmosphere, high salinity and high UV radiation exposure. As
a result, extremophile lifeforms were the only living organisms that were able
to survive the conditions. (Frances Westall, 2002) Since then, the
lifeforms have evolved into multicellular organisms in an environment that sustains
a wider variety of organisms, however extremophiles still inhabit remote
locations around the world.

What are extremophiles?

Extremophile lifeforms are organisms that are able to reside
in extreme conditions considered inhospitable to many other organisms. Often
these environments will have drastic temperatures, pH , pressure or salinity
levels uninhabitable for other lifeforms. Of these extremophiles there are
several types including: thermophiles, psychrophiles, acidophiles,
alkaliphiles, barophiles and halophiles. (Rampelotto, 2013)

Types of Extremophiles

Thermophiles

Thermophiles are lifeforms that are able to thrive in high temperature
conditions, with there being 3 main types of thermophiles: thermophiles,
extreme thermophiles and hyperthermophiles. (Francesco Canganella, 2014) In general
thermophiles have optimal growth occurring in the temperature range of 60-108
degrees Celsius. Unlike other organisms with enzymes that denature at high heat,
Thermophiles contain unique enzymes known as “extremozymes” which continue to
function. This is due to the enzyme’s ability to preserve their 3D structure in
those temperatures. (Beal, 2018) These lifeforms are
usually found in environments such as volcanic sites, hydrothermal vents, hot
springs and even man-made environments such compost piles. (Francesco Canganella, 2014) An example of a hyperthermophile
would be the “Methanopyrus kandleri” which
thrives in vents on the ocean floor at a temperature of 122 degrees Celsius. (Rampelotto, 2013)

Psychrophiles

On the contrary to Thermophiles, Psychrophiles are lifeforms that resides
in low temperature conditions, ranging from 20 degrees to sub zero temperatures.
For psychrophiles, the optimal growth is at a temperature of 15 degrees Celsius
and below, while minimal growth temperature would be sub zero. As a result of
this, many adaptions are required to ensure the survival of the lifeform such
as membrane fluidity, antifreeze proteins, cold adapted enzymes, etc. The capability
of the membrane to continue to be fluid at low temperatures is an important
characteristic as it allows the cells to intake nutrients. Furthermore, antifreeze
proteins along with cold adapted enzymes also help Psychrophiles survive in low
temperatures as the effects of ice crystallization is reduced along with the
lifeform’s optimal temperature. (Craig L Moyer, 2017)

Image
source: http://embor.embopress.org/content/15/5/508

Locations in which Psychrophiles can be found include the artic
permafrost, super cooled cloud droplets and rocks within the Antarctic dry
valleys. (Feller, 2013) Some examples of
this type of lifeform would be Psychromonas ingrahamii and Psychrobacter arcticus
which both have growth temperatures at -12 and -10 degrees Celsius
respectively. (Craig L Moyer, 2017)

Acidophiles

Acidophiles
are lifeforms that are able to settle in acidic environments, often with a pH
of approximately 3 being optimal for growth. However, these organisms are not
able to tolerate a low pH within their cell membrane, as a result pH
homeostasis is a crucial part of its adaption in this environment. One of it’s
main adaptions would be its highly impermeable cell membrane to protons. This
will help maintain the internal pH of the cell as a low pH is caused by a high
concentration in protons, in this case the hydrogen atoms. Additionally,
another method used to maintain a balanced pH is through pumping out excess
protons from within the cell, thus increasing the pH level. Furthermore, a
chemical gradient is also utilised to prevent a large intake of the hydrogen
protons. (Craig Baker-Austin, 2007) (Below is a visual
representation of some of these adaptations)

These acidophilic lifeforms are found in acidic environments such as
hydrothermal vents, sulfuric pool and geysers. One example of this would be Picrophilaceae,
an organism which has an optimal pH level of approximately zero. (Zinni, 2017)

Alkaliphiles

Conversely, Alkaliphiles are lifeforms which are adapted to a basic
environment with high pH levels of approximately 9. Similar to Acidophiles, they
have a cell membrane and a chemical gradient which assists in regulating a
relatively neutral pH range of 7-8.5 within the cell. Alkaliphiles are found in
basic environments such as soda deserts and lakes with one example being “Natronobacterium magadii” in
Lake Magadi, Kenya which has an optimal pH level of 10. (Eissa, 2017)

Barophiles

Barophiles are organisms with the capability of thriving in high pressure
environments, usually at pressures greater than 400 atm. There are two main
types of Barophiles known as obligate barophiles for pressures of 400-500 atm
and extreme barophiles for pressures greater than 500atm. (Prasanna Kondepati) Consequently, adaptations
are required for these high pressure environments, in order for these organisms
to survive. A main adaptation is the reduced amount of amino acids within the
proteins of Barophiles, resulting in more rigid proteins that are less likely
to deform under pressure. Furthermore, the cell membrane is found to contain
greater amount of poly unsaturated fatty acids (PUFAs), hence membrane fluidity
is increased allowing for cell to function normally at these great pressures. These
lifeforms are found in areas of deep seas such as the Marianis Trench in the
Pacific Ocean. (Munn, 2003) An example of a Barophile
would be the bacteria “Colwellia MT41” which is able to survive in temperatures
of 8 degrees and a pressure of 103 MPa. (Prasanna Kondepati)

Halophiles

Halophiles are a form of extremophiles that are able to survive in
environments of high salinity which would have otherwise cause detrimental
damage to other lifeforms. Because of this, certain adaptations are required
with there being two main strategies called 
the “salt in” and “osmolyte” strategy. The “salt in” involves potassium
ions being pumped into the cell, as a result increasing the salt concentration.
Thus this leads to a balanced concentration inside and outside the cell,
preventing water loss from occurring. In contrast, the “osmolyte” method
involves rejecting salt from the cell but instead intaking compatible solutes
that do not affect the functions of the organisms as a high solute
concentration is maintained. (Munn, 2003) Halophiles are found
in areas of high salt concentration such as salterns (ie Dead Sea) brine pools
and natural salt lakes . One example of a Halophile is “Haloquadratum” which is
known to colour saltern ponds pink-red. (Yanhe Ma, 2010)

Possibility of Extra-terrestrial Life

Extremophiles are lifeforms that are able to reside in the
harshest conditions, that otherwise normal organisms cannot. Thus, these
adaptable organisms open up various possibilities for extra-terrestrial life. Mars
being one of the planets that once had an environment similar to early Earth,
has a considerable potential of being a habitat to extra-terrestrial life that
are similar to extremophiles. (Frances Westall, 2002) Additionally, one of
Jupiter’s moon “Europa” is also a candidate for extra-terrestrial life as it
contains all the essential elements for life, including water, organic molecules
and energy despite its harsh icy environment. (Redd, Jupiter’s Icy Moon Europa: Best Bet for Alien Life?, 2014)

 

Mars

Early
Mars

The early conditions in Mars were hypothesised to be similar to early
Earth with there being an abundant source of water throughout the planet which
is essential for life. However, there were also many differences, one of which
was the high CO2 concentration
within the atmosphere compared to earth. This would have caused the water to
become more acidic and theoretically could have supported acidophilic lifeforms.
Additionally, due to the large amounts of shallow water that existed along with
salts, it was hypothesised the water sources had high salinity which would have
been a habitable environment for halophiles. Moreover, early Mars was also
thought to have volcanic activity, hot springs and a greater temperature range
than earth. Consequently, hyperthermophiles and hyperpsychrophiles may have
existed. From this, we are able to conclude that early Mars had the potential
to accommodate for extra-terrestrial life that were similar to the likes of
extremophiles. (Frances Westall, 2002)

Present-day
Mars

Since the early conditions, Mars has developed into a dry and barren planet.
However, in 2015 “recurring slope lineae” also known as RSL were discovered to
be caused by salty water that had run down the slopes (as shown in diagram
below). (Redd, Water on Mars: Exploration & Evidence,
2017)
Along with the study by the Space telescope Science Institute and University of
Maryland, where they were able to conclude halophiles are able to grow within
the temperature range of present day Mars, we can deduce that present-day Mars may
present a suitable environment for halophiles. This is due to the presence of
high salinity water and a temperature range halophiles are able to thrive in. (Could microbes survive
on Mars?, 2006)

 

Image Source: https://www.jpl.nasa.gov/spaceimages/images/largesize/PIA17727_hires.jpg

 

 

Europa

Jupiter’s moon, Europa has also recently been subject to theories that it
would support extra-terrestrial life. Although it does not seem like a place
for life to thrive with a surface temperature of -160 degrees Celsius, it contains
all the essential elements for life. (Howell, 2016) With the surface
being a frozen layer of ice, water lies below protected from dangerous
radiation. Furthermore, with NASA’s Hubble Space Telescope revealing geysers in
the moon’s southern hemisphere and the theory of vents under the surface of
Europa, the possible existence of extra-terrestrial life similar to Barophiles,
Thermophiles and Psychrophiles is suggested from the high pressure environment
with a vast range of temperatures. (Redd, Jupiter’s Icy Moon
Europa: Best Bet for Alien Life?, 2014) Supplementary
evidence that supports the theory of possible extra-terrestrial life includes
the surface with similarities to the theory plate tectonics and the production
of 10 times the oxygen compared to hydrogen, both of which are conditions
similar to Earth. (Howell, 2016)

Image Source: http://www.bbc.com/news/science-environment-38925601

Conclusion

Extremophiles are organisms that have been thriving since the existence
of early Earth, marking the extremities organism are able to survive in. As a
result, given our understanding of extremophiles, we have broadened our
understanding on the endless possibilities of extra-terrestrial life in our
universe.

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