Surviving the Unsurvivable

How extremophiles endure the most hostile habitats on Earth by Ella

Carnegie-Brown

Earth is peppered with harsh environments. From deadly pressures to extreme temperatures, lack of oxygen to high acidity, one might assume that life could not survive in these conditions. In spite of this presumption, there are organisms that thrive in these environments called extremophiles (NOAA, 2019). This name comes from the Latin extremus and Greek philia meaning “extreme-lovers” (Schröder, Burkhardt, Antranikian, 2020). Life as we know it needs two instruments for it to thrive; food and water. Every living organism needs to acquire energy and no matter what biome you examine on Earth, all of them share the same requirements for energy and water (NOAA, 2022). However, the bizarre and unique discovery of these organisms can tell scientists all about the range of conditions in which life can be possible.

About extremophiles

Extremophiles are of biotechnological interest as they are predominantly prokaryotic (archaea or eubacteria) but possess a fascinating adaptation allowing them to produce enzymes called extremozymes. These remarkable catalysts can convert substrates under harsh conditions. There are a vast variety of different extremophiles depending on their environment. Some are called hyperthermophiles which grow at temperatures from 80°C all the way up to 110°C. These special organisms can be found thriving in deep water where the mantle of the Earth’s core escapes from the seabed. These vents can reach up to an astounding 400°C. Additionally, the variety includes alkaliphiles (pH 9-12) and acidophiles (pH 0.5-4) (see Fig.1), (Schröder et al, 2020). Moreover, within the deepest parts of the ocean, piezophiles can be found. These unique organisms can withstand intense pressures. Expanding into more detail, we can delve into how extremophiles are adapted to their extreme environments.

Hyperthermophiles

Hyperthermophiles cannot be protected by insulation against their environment. Therefore every single cell component has to be resistant to heat to maintain survival. The molecular basis for this case is unknown and still under investigation. Lipids, proteins and nucleic acids all react to heat and are fairly sensitive. Therefore the lipid membrane they have contains a novel glycerol ether lipid. This can stabilise and maintain the membrane against hydrolysis at very high temperatures. For archaeal hyperthermophiles, to protect their DNA (which is usually very sensitive to heat), they use a special histone which changes the shape of the chromosomes and thus increases the DNA’s melting temperature (Rogers, 2023). When reaching 100°C, ATP begins to hydrolyse very fast and amino acids will begin to decompose. Any hyperthermophiles that can withstand a higher temperature than this could only do this by rapidly re-synthesising compounds. Therefore, the highest temperature hyperthermophiles could survive would be at 113-150°C (O. Stetter, 2019).

Acidophiles

Acidophiles are microorganisms that grow in extremely acidic environments. Many fungi and bacteria are acidtolerant; however, microbes can withstand extreme acidity. The Picrophilus is an archaebacteria which is one of the most acidophilic microorganisms ever known. It can fascinatingly grow at a pH below 0. The way acidophiles can survive their hostile conditions is due to their durable cytoplasmic membranes. To maintain the stability of the membrane they require a very high concentration of hydrogen ions. The structure of their membranes are obviously different to other microorganisms as they have evolved to contain many glycoproteins which make the cytoplasmic membrane durable within a hot and acidic condition. Many of these acidophiles have unusual arrangements of lipids which form a strong membrane that can help the organism survive in an extremely acidic habitat (Garg, 2016).

On the opposite side of the pH scale, we find a complete contrast of extremophiles called alkaliphiles which are microorganisms that thrive and grow at pH values above 9. These microorganisms have been discovered to have incredible adaptations which has benefited industrial purposes as they can produce alkali enzymes such as alkaline proteases and alkaline celluloses which is used in the laundry detergent market (Horikoshi, 1999). Alkaliphiles can be found in highly acidic soils and faeces, whereas haloalkaliphiles (alkaliphiles requiring a pH above 9 and a high salinity) can be found within Serbian lates such as Rift Valley Lakes of east Africa. For these extremophiles, their survival relies on maintaining homeostasis and the intake of H+ ions. They protect themselves from the alkaline surroundings using acidic substances like amino acids. Some alkaliphiles increase their hydrophobic interactions and negatively charged amino acids at the interface for stability in their environment (Salwan et al, 2020).

Psychrophiles

In contrary to hyperthermophiles, we can delve into the harsh freezing environment where psychrophiles are found. They must overcome reduced enzyme reactivity, a decreased membrane fluidity, different transport of nutrients and waste products, slower rates of cell division, protein denaturing and proteins folding differently. Which all these challenges, psychrophiles have evolved to overcome every single one and can successfully thrive in extremely cold and icy conditions. The lowest temperature life can survive is −24 °C, at these temperatures both aerobic and anaerobic organisms can be found such as the lichen Xanthoria elegans (see Fig.2). To overcome membrane fluidity, psychrophiles has an altered lipid composition, there is a higher amount of unsaturated fatty acids, there is an increased number of lipid head groups which result is a decreased number of interactions in the membranes. As for cell division, protein synthesis occurs at a reduced rate. The enzymes that are used for translation and transcription are adapted to function at low temperatures, an example of this is their RNA polymerase which has evolved to be optimally active. Psychrophiles contain antifreeze proteins which are a remarkable and significant feature as they have the ability to bind to ice crystals and thus they can create the ram hysteresis and lower the temperature which the organism can grow. Therefore the psychrophile is an incredible form of life that can withstand its hostile environments (D’Amico 2006).

New research

These remarkable organisms give a new insight into a world of research with is beneficial to humans. We can use our knowledge of extremophiles for biotechnology all research. All the extremophiles previously discussed can go through cell division and multiply in their environments. Due to these fascinating adaptations, scientists can use them to produce significant biomolecules which can withstand extremely hot or cold temperatures and acidic or alkaline environments. There are of course many different types of extremophiles which are also undergoing research. These biomolecules can perform different abilities at industrial levels. An example of these abilities is biodegradation, sources of biofuel and bio energy. For biodegradation, many extremophiles microorganism contain enzymes which are robust and versatile; an example of an extremozyme is Bacillus safensis which contains the enzyme oxidoreductase which can degrade aromatic compounds. Furthermore, many enzymes have an important role in chemical, food, paper and waste-treatment industries (Shukla et al, 2020). Therefore, extremophiles can play a predominant role within the future of a sustainable earth benefitting humans across the globe.

Astro biology

Due to their robust structure, extremophiles push the boundaries of life on Earth. They are therefore of interest to astrobiologists curious about exploring life beyond earth. Planets with harsh environments similar to those in which extremophiles can survive may be home to organisms with similar extreme physiological and biochemical adaptations. Scientists have found an extremophile called the Haloarchaea These are anaerobes that can grow with or without the presence of oxygen. Furthermore, they can tolerate many extremes and is the key microorganisms in which astrobiologists believe could expand our knowledge on life in space. To begin with the study of life on other planets, we must understand evolution and habitability as this allows organisms to adapt and survive. Evolution is caused by a random mutation that occurs in the DNA sequence. The mutation could be beneficial and increases survival chances making the organism more likely to pass on its alleles which could include the survival benefactor. The perfect case for this is the Haloarchaea as it represents the perfect model for astrobiology as it has evolved to survive in many different extreme conditions, therefore they possibly evolved very early on Earth. Due to the ancient microorganisms, they could possible survive on Mars as they can survive exposure to radiation, sub-zero temperatures and remarkably, they have been discovered to survive the process of launching them into the stratosphere with high exposures to the conditions of space. Further research includes the proof that Haloarchaea constrain highly acidic proteins. With these proteins, they can maintain an osmotic equilibrium within very salty concentrations. Lastly, with future modelling studies there are plans for astrobiological observations which could lead to new discoveries and potentially answer the question of the existence of life in space and if it is possible (DasSarma et al, 2021).

Extremophiles are an incredible life form that can give scientists further understandings into pushing the boundaries of life. With this knowledge on extremophiles, we can produce biodegrading enzymes and medicine, extremophiles serve a purpose in industrial levels and help benefit society. They also give scientists hope for new life as certain extremophiles could possibly be adapted for another planet. Therefore, with the continuous research produced everyday, we could possibly answer some very important questions about humanity and life based off these incredible organisms.

Discussion questions

1. What is the most hostile environment an extremophile can be found in?

2. What are the challenges of studying extremophiles as a career?

References

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Interested in learning more?

Here is a short video from National Geographic:

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