An extreme environment is a habitat characterized by harsh environmental conditions further than the optimal range for the development of humans or other living organisms.

Extreme environments are characterized by various unfavorable conditions including, high or low temperature, high or low pressure, and acidic or basic pH.

For an area to be considered extreme, certain conditions or aspects of the environment must be considered very hard for different forms of life to survive.

Examples of some extreme environments include the polar region, deserts, volcanic regions, deep ocean trenches, outer space, and every other planet of the Solar System except the Earth.

Some of the common extreme environments include areas that are alkaline, acidic, extremely hot or cold, high salt concentration, without water or oxygen.

Extreme environments are classified into the following groups based on the extreme physicochemical conditions:

Extreme temperature: Two types of extreme environments can be described; cold and hot.

• Extremely cold environments are those with environmental temperatures below 5°C. These can be found in deep ocean niches, at the peaks of high mountains, or the Polar Regions.
• Extremely hot environments are characterized by environmental temperatures higher than 45°C. These environments are influenced by geothermal activity as geysers and fumaroles of continental volcanic areas or deep-sea vents.

Extreme pH: Extreme environments can also be classified as acidic or alkaline according to their pH.

• Extreme acidic environments are natural habitats in which the pH is below 5.
• Extreme alkaline environments are those with a pH above 9.

Extreme ionic strength:

• Hypersaline environments are environments with an ionic concentration higher than of seawater (greater than 3.5%).

Extreme pressure:

• Extreme pressure environments are those environments under extreme hydrostatic or litho pressure, such as aquatic habitats at depths of 2,000 m or more or deep-subsurface ecosystems.

High-radiation environments are those areas that are exposed to abnormally high radiation doses, including ultraviolet or gamma radiation, like deserts and the top of high mountains.

Xeric environments are arid habitats with limited water activity. Cold and hot deserts are some examples of these extreme environments.

What are extremophiles?

• Extremophiles are living organisms with the ability to survive and thrive in extreme environments as a result of different physiological and molecular adaptations.
• These organisms thrive in extreme niches, ice, and salt solutions, as well as acid and alkaline conditions.
• Some might grow in toxic waste, organic solvents, heavy metals, or in several other habitats that are considered inhospitable for life.
• Most extremophiles are prokaryotic organisms with few eukaryotes. These extremophiles are defined by the environmental conditions in which they can survive and thrive optimally.
• Extremophiles can be divided into two categories: extremophilic organisms that require one or more extreme conditions to survive, and extremotolerant organisms that can tolerate extreme conditions of one or more physical parameters even though they grow optimally at neutral conditions.
• Extremophiles include members of all three domains of life; bacteria, archaea, and eukarya.
• Most extremophiles are prokaryotes with a high proportion of belonging to archaea, but some organisms might be eukaryotes such as protists (e.g., algae, fungi, and protozoa) and multicellular organisms.
• These are classified according to the conditions in which they grow: thermophiles and hyperthermophiles (organisms growing at high or very high temperatures, respectively), psychrophiles (organisms that grow at low temperatures), acidophiles and alkaliphiles (organisms thriving in habitats with acidic or basic pH values, respectively), barophiles (organisms that grow best under pressure), and halophiles (organisms that grow well in an environment with NaCl).

Characteristics of extremophiles

• Extremophiles are characterized by the ability to thrive in extreme environments which results from different forms of physiological and molecular adaptations.
• Extremophiles are mostly prokaryotes with the nuclear material in the cytoplasm and unicellular eukaryotes.
• Archea is an important group of organisms that tend to be extremophiles due to their ability to adapt to different extreme conditions.
• These organisms present a wide and versatile metabolic diversity, along with extraordinary physiological capacities to inhabit extreme environments.
• These forms of adaptations are developed through various evolutionary processes over a long period of time.

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Applications of Extremophiles

• Exremophilic enzymes have been model systems to study enzyme evolution, enzyme stability, activity, mechanism, protein structure, function, and biocatalyst under extreme conditions.
• Thermophiles have yielded stable α-amylase for starch hydrolysis, oxylonases for paper bleaching, and proteases for brewing and for detergent purposes.
• Alkaline active proteases, amylases, cellulases, mannanases, lipases, etc. are used in the formulation of heavy-duty laundry and dishwashing detergents as they are efficient in removing stains and allow effective low-temperature (30–40°C) washing.
• Some species of acidophilic microorganisms can be used not only to reduce mine water pollution but also to recover metals from acidic wastewater via selective biomineralization.
• Extroenzymes like Taq polymerase from Thermus aquaticus is an ideal for use in a polymerase chain reaction as it reduces the need for adding extra polymerase during the reaction.
• Cellulose for various extremophilic organisms has been used for the treatment of juices, color brightening in detergents, and treating cellulose-containing biomass and crops to improve their digestibility and nutritional quality.
• Similarly, halophiles are being exploited as a potential source of carotene, compatible solutes, glycerols, and surfactants for pharmaceutical use.
• Some extremophilic microorganisms may also comprise a large reservoir of novel therapeutic agents—for example, iron-binding antifungal compound, pyochelin isolated from halophilic species of Pseudomonas.
• A thermostable glucokinase from the thermophilic species, Bacillus stereothermphiolus, can be used as a glucose sensor for quick glucose assay.
• Alkaline active enzymes have got several notable applications in textile and fiber processing in processes like cotton scoring and blast fiber degumming.
• Alkaliphiles and their enzymes have been tried in various synthesis reactions with peptide synthesis being the most important one.
• Information on the microbial composition and biogeochemical cycling of extreme ecosystems also helps in understanding the global change, threats, and opportunities for living beings.
• Enzymes from extremophiles can also be used in bioremediation processes like toxifying wastewater and air and removing metallic waste from sewages and industries.
• Different barophilic enzymes are used for the production and sterilization of items at varied pressure conditions.