This document provides an overview of extremophiles, which are microorganisms that thrive in physically or geochemically extreme conditions. It begins by defining extremophiles and their classification based on extreme habitats. It then discusses various types of extremophiles in more depth, including thermophiles and hyperthermophiles that grow at high temperatures, psychrophiles that grow at low temperatures, acidophiles and alkaliphiles that grow at extreme pH, and barophiles that live under high pressure. For each type of extremophile, examples are given and their adaptations to survive in extreme conditions are described.

1. EXTREMOPHILES
Life under extreme conditions
• Ranjeet Kumar Taram
• MSc.III sem (Microbiology)
• S.o.S. in Life Science
• Pt. Ravishankar Shukla University, Raipur
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2. CONTENTS
1. Introduction
2. Classification
3. Extreme in temperature
4. Extreme in pH
5. Extreme in pressure
6. Extreme salinity
7. Low nutrient concentration
8. Low water availability
9. Absence of oxygen
10. High ionizing radiation
11. Metal resistance
12. Biotechnological applications
13. Astrobiology
14. References
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3. INTRODUCTION
• Latin origin- “Extremus” means ‘Being on the outside’ PLUS “Philos” means ‘Love’ =
EXTREMOPHILE
• Extremophile- An organism with the ability to thrive in extreme environments.
• Coined by Bob McElroy- was the biochemist in the Adaptation Branch in NASA Ames.
• Basically extremophiles denote the microorganisms that live in
physically/geochemically extreme conditions that are mostly detrimental for other
forms of life .
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4. CLASSIFICATION
• Extremophiles are classified on the basis of their extreme habitat where they live.
• There are different types of extreme conditions where microorganisms are inhabit.
➢ Temperature- high, low
➢ pH- high, low
➢ Pressure- high
➢ Salinity- high
➢ Nutrient concentration- low
➢ Water availability- low
➢ Oxygen availability- low
➢ Ionizing radiation- high
➢ Harmful heavy metals and toxic compounds- high
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Fig. Phylogenetic tree showing Extremophiles and their resistant characteristics.

6. EXTREME IN TEMPERATURE:-
Organisms that can thrive in wide range of temperature.
• Types:-
➢ i. Hyperthermophile: Growth >80°C
➢ ii.Thermophile: Growth 60-80°C
➢ iii.Mesophile: Growth 15-60°C
➢ iv. Psychrophile :Growth -15 to 15°C
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7. Thermophiles :-
➢ Greek- thermotita (heat) and philia (love)
➢ Grows in a temperature range of 60-80 °C
➢ Mostly found in geothermally heated regions on earth viz.,
hot springs, hydrothermal vents etc.
➢ As they need extreme temperature, its very hard to study
them under laboratory conditions.
➢ Also that some members can produce heat by themselves
(compost and garbage landfills).
➢ Ex : Cyanidium caldarium, Chaetomium thermophile etc.
Hot spring
Hydrothermal vent
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8. ➢ Hyperthermophiles were first discovered by Thomas D. Brock in 1965, in hot springs in Yellowstone
National Park, Wyoming.
➢ At present- about 90 species of hyperthermophilic archaea and bacteria are known.
➢ Most hyperthermophilic organism – Archaea Pyrolobus fumarii- can thrive up to 113 °C.
➢ Archaea Methanopyrus kandleri- can thrive upto 122 °C .
➢ Other- Geogemma barosii ,Nanoarchaeum equitans, Thermus aquaticus, Pyrococcus furiosus.
Hyperthermophile :-
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9. • Membrane lipids have ether linkage- more branched, more saturated and are of high molecular weight.
These characters increase melting temperature of membrane lipids.
• Hyperthermophiles, most of which are Archaea, do not contain fatty acids in their membranes but
instead have C40 hydrocarbons composed of repeating units of isoprene bonded by ether linkage to
glycerol phosphate.
• The membrane forms a lipid monolayer rather than a lipid bilayer .
• This structure prevents the membrane from melting (peeling apart) at the high growth temperatures of
hyperthermophiles.
• Heat stability of proteins in hyperthermophiles is also bolstered by an increased number of ionic bonds
between basic and acidic amino acids and their often highly hydrophobic interiors; the latter property
is a natural resistance to unfolding in an aqueous cytoplasm.
Adaptation mechanism of Thermophile :-
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10. • Finally, solutes such as di-inositol phosphate, diglycerol phosphate, and mannosylglycerate are
produced at high levels in certain hyperthermophiles, and these may also help stabilize their
proteins against thermal degradation.
• Heat shock proteins- more hydrophobic interiors- prevents unfolding or denaturation at higher
temperatures
• High GC content than AT content in nucleic acid structure.
• Reverse DNA gyrase enzyme- catalyzes positive supercoiling of closed circular DNA- Positively
supercoiled DNA appears to resist degradation more than negatively supercoiled DNA.
• DNA association with DNA binding histone like protein.
• Salts like potassium and magnesium are found at higher levels in thermophilic archaea- protect
double-stranded DNA from phosphodiester bond degradation.
• Thick pseudo-crystalline proteinaceous surface layer (Slayer) surrounding cell.
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11. • Temperature range is -15 to 15 °C , Also known as cryophiles.
• Have an optimum temperature of 15 °C or lower .
• Isolated from Arctic and Antarctic habitats (90% of the ocean is 5 °C or colder).
• 20% of the terrestrial region of the Earth is, glaciers and ice sheets, polar sea ice and snow covered regions.
• Psychrophilic microbial communities containing algae and bacteria grow in dense masses within and under
sea ice (frozen seawater that forms seasonally) in polar regions.
• The common snow alga Chlamydomonas nivalis is an example of this.
• In addition to snow algae, several psychrophilic bacteria have been isolated, mostly from marine sediments
or sea ice, or from Antarctica.
• Psychromonas and Polaromonas species are common.
Psychrophiles :-
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12. • Some of them cause spoilage in refrigerated food materials.
• Ex: Arthrobacter spp., Psychrobacter spp., Halomonas spp., Pseudomonas, sphingomonas.
• Methanogens, members of Archaea, are the only group known to be Psychrophiles (Ex.
Methanococcoides burtonii)
• A Nematode Panagrolaimus davidi- can withstand freezing of all body water.
Adaptation mechanism of Pyshrophile :-
The greater 𝛼 −helix content of cold-active enzymes allows these proteins greater flexibility for
catalyzing their reactions at cold temperatures.
Cold-active enzymes also tend to have greater polar and lesser hydrophobic amino acid content than their
mesophilic and thermophilic counterparts .
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13. • Cytoplasmic membranes from psychrophiles tend to have a higher content of unsaturated and shorter-
chain fatty acids. This helps the membrane remain in a semifluid state at low temperatures.
• the lipids of some psychrophilic bacteria contain polyunsaturated fatty acids, something very
uncommon in prokaryotes. For example, the psychrophilic bacterium Psychroflexus spp. contains fatty
acids with up to five double bonds.
• Other molecular adaptations to cold include “cold-shock” proteins and cryoprotectants. Cold-shock
proteins are a series of proteins that have several functions including helping the cell maintain other
proteins in an active form under cold conditions or binding to specific mRNAs and facilitating their
translation.
• Cryoprotectants include dedicated antifreeze proteins or specific solutes, such as glycerol or certain
sugars that are produced in large amounts at cold temperatures; these agents help prevent the
formation of ice crystals that can puncture the cytoplasmic membrane.
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Fig. - Physiological adaptation in psychrophiles

15. EXTREME IN PH:-
• On the basis of pH microorganisms can be classified as :-
• i.Acidophiles ii.Alcaliphiles
• Organisms that lives in highly acidic environments are called as acidophiles.
• They grow best below pH 5.5.
• Some members that mainly found in the drainage of coal mines are able to oxidize sulfur into sulfuric
acid.
• Mechanism of action is that they have a proton pump machinery to maintain low pH.
• Ex.-Sulfolobus acidocaldarius , Hydrogenobaculum acidophilum , Alicyclobacillus acidocaldarius ,
• Algae - Cyanidium caldarium
Acidophiles :-
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16. • Sugar coating on acidophilic archaea- act as proton barrier apart from tetra ether linkage in
monolayer lipids, there is also high content of glycolipids, with one or more sugar units exposed at
the outer surface of the cell.
• Hydroxyl groups on the sugar units prevent the protons from penetrating the cell membrane.
Adaptation mechanism of acidophiles :-
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17. • These are extremophilic microorganisms which
thrives in roughly alkaline environments (8-11), and
have an optimum of pH around 10.
• Alkaliphilic microorganisms are typically found in
highly alkaline habitats, such as soda lakes and high-
carbonate soils.
• The most well-studied alkaliphilic prokaryotes are
certain Bacillus species, such as Bacillus firmus.
• Ex.-Halorhodospira halochloris , Natronomonas
pharaonis , Thiohalospira alkaliphila ,
Ectothirorhodospira , Bacillus alcalophilus ,Bacillus
subtilis , Bacillus pseudofirmus etc.
Alcaliphiles:-
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18. • By having cytoplasm rich in amino acids with positively charged side groups (lysine, arginine, and
histidine), these cells are able to buffer their cytoplasm in alkaline environments.
• By low membrane permeability which is another mode of passive regulation as it ensures that fewer
protons move in and out of the cell.
• Presence pH stable enzymes in alkaliphilic organisms.
• In addition to peptidoglycan, cell wall contain certain acidic polymers, such as galacturonic acid, gluconic
acid, glutamic acid, aspartic acid, and phosphoric acid.
• The negative charges on these acidic non-peptidoglycan components may give the cell surface its ability to
adsorb sodium and hydronium ions and repulse hydroxide ions and, as a consequence, may assist cells to
grow in alkaline environments.
Adaptation mechanism of alcaliphiles :-
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19. EXTREME IN PRESSURE
(BAROPHILES)
• Organisms that live in highly pressurized environments, such as the bottom of the ocean.
➢ Barotolerants (facultative): Grows at pressure from 100-400 Atm.
➢ Barophilic (obligative): Grows at pressure greater than 400 Atm.
➢ Extreme Barophilic: Grows at pressures higher than 700 Atm.
➢ These organisms cannot grow in pressure below 400-500 atm.
• True obligate barophiles also comprises bacteria which present in the gut of holothurians
and amphipods (crustaceans).
• Eg: Photobacterium, Shewanella, Colwellia.
• Some thermophilc archaea such as Pyrococcus spp., Methanococcus jannaschii are barophiles
too.
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20. • Lipids contain Unsaturated fatty acids (PUFA)- protect from the pressure.
• Proteins coat (Outer membrane proteins) -protects from the pressure.
• Proteins/enzymes hold the cellular structure together by allowing the normal chemical reactions
to take place.
• Pressure controlled gene expression.
Adaptation mechanism of barophiles :-
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21. EXTREME SALINITY
(HALOPHILES)
• Organisms that can survive in extremely salty environments such as The Great Salt Lake and Dead Sea.
• According to the optimal salt concentration for growth classified in three categories:
• Extreme halophile—Grows in an environment with 3.4–5.1 M (20% to 30%) NaCl.
• Moderate halophile—Grows in an environment with 0.85–3.4 M (3% to 25%) NaCl.
• Slightly halophile—Grows in an environment with 0.2–0.85M (1% to 5%) NaCl.
• Most of the halophiles belong to the Domain Archae.
• Eg: Salinibacter ruber,Halobacterium , Haloarcula vallismortis , Haloferax volcanii.
• There are eukaryotic halophiles such as Dunaliella salina (algae) and Wallemia icthyophaga (fungus).
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22. • Mainly employ two mechanism to prevent desiccation through osmosis.
• Both strategies work by increasing the osmotic concentration of the cell.
✓ “High salt in” strategy –
➢ Internal environment has a high salt concentration by influx of KCl.
➢ therefore organism is isotonic to its outer environment.
➢ prevents water from moving in and out of the cell, which regulates osmosis and maintains the
structure and function of the cell in turn.
✓ “Low-salt, compatible organic-solutes-in” strategy –
➢ Organisms store organic compatible solutes (osmoprotectants) in their cells.
➢ these organic compatible solutes regulate osmosis.
➢ these are neutral or zwitterionic include sugar, polyols, amino acids etc.
Adaptation mechanism of halophiles :-
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23. NUTRIENT CONCENTRATION- LOW
(ENDOLITHS)
• Endolith is an organism (archae, bacterium, fungus, lichen or algae) that lives in nutritionally poor
environments such as inside a rock or something.
• Particularly interesting in the area of astrobiology (exobiology).
• These organisms opens a clue for life beyond earth. There are chances of having life on endolithic
environments such as mars and other planets.
• Endoliths have been found in rocks down to the depth of 3 km.
• All the discovered organisms are autotrophs.
• Some utilize gas or dissolved nutrients from water moving through fractured rocks.
• Others may incorporate inorganic compounds found in their rock substrate (possibly by excreting acids
to dissolve the rock).
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24. WATER AVAILABILITY- LOW
(XEROPHILE)
• A xerophile (from Greek xēros , meaning "dry", and philos, meaning "loving"), is an extremophilic
organism that can grow and reproduce in conditions with a low availability of water.
• Water activity (aw) is a measure of the amount of water within a substrate an organism can use to
support sexual growth.
• Xerophiles are often said to be "xerotolerant", meaning tolerant of dry conditions. They can survive
in environments with water activity below 0.8.
• Endoliths and halophiles are often xerotolerant.
• Eg: many molds and yeast, Trichosporonoides nigrescens.
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25. ABSENCE OF OXYGEN
(OBLIGATE ANAEROBES )
• Obligate Anaerobes:-
• Microorganisms which grow strictly in the absence of molecular oxygen are called as obligate anaerobes.
• For these, oxygen is a toxin.
• For energy generation, they must employ fermentation or anaerobic respiration pathways.
• The toxic forms of oxygen are Singlet Oxygen(O2*), Superoxide radicals (O2
- ), peroxide anion (O2
-2 ), and
hydroxyl radical (OH).
• Some obligate anaerobes are Clostridium spp, Methanococcus and Methanopyrus.
• Microorganisms which can live both in the presence and absence of oxygen are known as Facultative
Anaerobes.
• They can utilize oxygen if available or, continue their growth by fermentation and anaerobic respiration.
• Eg: Bacillus anthracis, Escherichia coli. 25

26. IONIZING RADIATION- HIGH
(RADIORESISTOR)
• Radioresistor :-
• Organisms resistant to high levels of ionizing radiation, most commonly UV radiation.
• Some capable of resisting nuclear radiation.
• Deinococcus radiodurans is the radioresistant organism discovered so far which is a eubacteria.
• Their ability to withstand radiation is more than that of endospores.
• The mechanism for this extraordinary resistance lies in a unique arrangement of its DNA that
facilitates a rapid repair of radiation damage.
• It is similarly resistant to many mutagenic chemicals.
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27. METALLOTOLERANT:-
• Metallotolerants are extremophiles that are able to survive in environments with a high concentration
of dissolved heavy metals in solution. Metallotolerants may be found in environments containing arsenic ,
cadmium, copper, and zinc.
• Known metallotolerants include Ferroplasma sp. and Cupriavidus metallidurans.
• Bioleaching of heavy metals from industrial contaminated soil using metallotolerant fungi is the most
efficient, cost-effective, and eco-friendly technique.
• Metallotolerant fungal strains including Aspergillus niger M1, Aspergillus fumigatus M3, Aspergillus
terreus M6, and Aspergillus flavus M7 were isolated and identified by pheno- and genotyping.
• A. fumigatus and A. flavus of soil sample S1 showed higher efficiency for Pb removal (99.20% and
99.30%, respectively).
• Leptospirillum ferrooxidans could grow using ferrous iron as sole source of energy, and that this
microorganism is mainly responsible for metal bioleaching and acid mine drainage generation.
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28. BIOTECHNOLOGICAL APPLICATION OF EXTREMOPHILES:-
Products Uses
DNA polymerases DNA amplification by PCR
Alkaline phosphatases diagnostics
Proteases and lipases Dairy products
Lipases and proteases Detergents
Proteases Baking, brewing, amino acid production from keratin
Alcohol dehydrogenase Chemical synthesis
Xylanases Paper bleaching
S-layer proteins and lipids Molecular sieves
Lenthionin pharmaceutical
Oil degrading microorganisms Surfactants for oil recovery
Sulfur oxidizing microorganisms Bioleaching, coal & waste gas desulfurization
Hyperthermophilic consortia Waste treatment and methane production
Hyperthermophiles
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29. Products uses
Alkaline phosphatase Molecular biology
Lipases and proteases Cheese manufacture and dairy production
Proteases Contact-lens cleaning solutions, meat tenderizing
Polyunsaturated fatty acids Food additives, dietary supplements
Methanogens Methane production
𝛽 − 𝑔𝑎𝑙𝑎𝑐𝑡𝑜𝑠𝑖𝑑𝑎𝑠𝑒 Lactose hydrolysis in milk products
Ice nucleating enzymes Artificial snow ,ice cream , other freezing applications in
the food industry
Proteases, lipases, cellulases and amylases Detergents
Oxidases Bioremediation,environmental biosensors
Pychrophiles
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30. Products uses
Bacteriorhodopsin Optical switches and photocurrent generators in
bioelectronics
Polyhydroxyalkanoates Medical plastics
Rheological polymers Oil recovery
Eukaryotic homologues (e.g. myc oncogene product) Cancer detection, screening anti-tumor drugs
Lipids Liposomes for drug delivery and cosmetic packaging
Compatible solutes Protein and cell protectants in variety of industrial uses,
e.g. freezing, heating
Compatible solutes Protein and cell protectants in variety of industrial uses,
e.g. freezing, heating
g-linoleic acid, b-carotene and cell extracts, e.g. Spirulina
and Dunaliella
Health foods, dietary supplements, food coloring and
feedstock
Membranes Surfactants for pharmaceuticals
lipids Liposomes for drug delivery and cosmetic packaging
Halophiles
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31. Products uses
Proteases Gelatin removal on X-ray film
Proteases, cellulases, xylanases, lipases Detergents
Elastases, keratinases Hide dehairing
Cyclodextrins Foodstuffs, chemicals and pharmaceuticals
Xylanases and proteases Pulp bleaching
Pectinases Fine papers, waste treatment and degumming
Alkaliphilic halophiles Oil recovery
Alkaliphiles
Acidophiles
Products uses
Sulfur oxidizing microorganisms Recovery of metals and desulfurication of coal
Microorganisms Organic acids and solvents
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32. • Astrobiology :-
• astrobiology, formerly known as exobiology, is an
interdisciplinary scientific field concerned with the origins, early
evolution, distribution, and future of life in the universe.
• Astrobiology considers the question of whether extraterrestrial
life exists, and if it does, how humans can detect it.
• Some extremophiles are found in space that are used in study of
exobiology.
• Tardigrades, known colloquially as water bears or moss piglets,
are a phylum of eight-legged segmented micro-animals
• Discovered in 1773 by a German zoologist Johann August
Ephraim Goeze.
• Microscopic animals - body size varies from0.05 to 1.2 mm.
• Can survive all extreme environments:
• a) 120 to 1500C high temperature
• b) 200 to 3000 below 00C
• c) 1000 atm high pressure
• d) Vacuum of space
• e) X-rays, UV rays
Boil them, deep-freeze them, crush them,
dry them out or blast them into space:
tardigrades will survive it all and come
back for more.
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33. REFFERENCES :-
Madigan, Michael T., et al. Brock biology of microorganisms 13th edition. Benjamin
Cummings, 2010.
Rainey, Fred A., and Aharon Oren. "1 Extremophile microorganisms and the methods
to handle them." Methods in microbiology. Vol. 35. Academic Press, 2006. 1-25.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4187170/
https://www.researchgate.net/figure/Phylogenetic-tree-showing-the-extremophiles-
and-the-resistant-characteristics-that-appear_fig1_274725946
https://link.springer.com/article/10.1007/s42398-019-00082-0
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