Extremophiles are microorganisms that thrive in extreme conditions detrimental to most forms of life, mainly belonging to the domain Archaea and including types such as thermophiles, psychrophiles, and halophiles. They possess specialized enzymes called extremozymes that are stable and functional under harsh conditions, making them valuable in various industrial applications. The document also explores the classification, habitats, and unique adaptations of these organisms, as well as their implications for astrobiology and the possibility of life beyond Earth.

1. MICROBIOLOGY
Jithin. V
EXTREMOPHILES

2. EXTREMOPHILES
 Organisms found living in extreme harsh environments.
 Word originated from Greek- Extremus + Philia which
means extreme loving.
 Most members of this group comes under the domain
Archae.
 These include thermophiles, hyperthermophiles,
thermoacidophiles, alkaliphiles, psychrophiles,
halophiles, barophiles, radiation resistant bacteria
and endoliths.

3. DEFINITION
Organisms lives in physically/geochemically extreme
conditions that are mostly detrimental for other forms of
life.
In other words, an extremophile is a
microorganism, mostly an Achaeon that lives in
conditions of extreme acidity, alkalinity, temperature,
salinity, pressure, nutrient scarcities etc.

4. HOW DO THEY LIVE SO?
 Extremozymes- specialized enzymes that
are highly stable.
 Can tolerate extremes of temperature, pH,
salinity that would inactivate other
enzymes.
 Important in industries because of this
property.

5. EXTREME CONDITIONS
 Temperature
 pH
 Salinity
 Nutritional scarcities
 Absence of oxygen
 Radiation
 Pressure

6. Response to Environmental factors

7. TYPES
Psychrophiles
 Temperatue range is -15 to 150
C
 Also known as cryophiles.
 Have an optimum temperature of 150
C or lower
 Isolated from Arctic and Antarctic habitats (90% of the
ocean is 50
C or colder)
 Also found in ice bergs, glaciers, snowfields etc
 Metabolism is quite normal at colder temperatures.
 Cell membranes-high levels of fatty acids which remain
fluid at colder temperatures.
 Proteinaceous antifreeze mechanism to protect the cell
and DNA
 Some of them cause spoilage in refrigerated food materials.
 Eg: Arthrobacter spp, Psychrobacter spp, Halomonas
spp, Pseudomonas, sphingomonas

8. FIRMICUTES
 Gram positive, spore forming bacterial family that
can survive desiccation and can survive extreme
conditions.
 This group also is an example for extremophilic
true bacteria (eubacteria).
 Plays an important role in the spoilage of beer, wine
and cider.
 Eg: Helicobacterium spp, Mycoplasma,
Clostridium spp.

9.  Many members of the Family Firmicutes are also
thermophiles.
 Eg: Bacillus stearothermophilus
 Recently, a DNA polymerase derived from these
bacteria, Bst polymerase has become important in
biotechnology.
 Bst polymerase- helicase like activity (making it
able to unwind DNA strands.
 Optimum functional temperature is 60-650
C and get
inactivated at temperatures above 800C

10. THERMOPHILES
 Greek- thermotita (heat) and philia (love)
 Temperature loving organisms.
 Most members are Archae
 Grows in a temperature range of 55-1130C
 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).
 Eg : Cyanidium caldarium,
Chaetomium thermophile

11.  Deinococcus-thermus is a small group of eubacteria
which can thrive environmental hazards.
 Stains Gram positive (thick cell wall) but possesses an
outer membrane, similar to the Gram negative cell wall.
 Several thermophilic bacteria comes under this group.
 It is the source of heat resistant enzyme- taq
polymerase, which is well used in PCR.
 The enzyme is isolated from Thermus aquaticus.

12. Grand Prismatic Spring and Midway Geyser Basin-
Yellowstone National Park, USA
Source: Internet

13. CLASSIFICATION OF THERMOPHILES
1. Obligate thermophiles
 Also known as extreme thermophiles.
 Temperature range is 80-1220
C.
 Membranes and proteins are unusually stable at
these extreme temperatures.
 For this reason, most biological processes utilize
thermophilic enzymes because of their ability to
withstand intense heat.
 Many of this group can resist radiation too.
 Eg: Methanopyrus kandleri, can survive and
reproduce at 1220
C, Sulfolobus spp , Pyrococcus
spp, Pyrodictium spp (optimum of 1130
C)

14.  Most of the members require elemental sulfur for
growth.
 Anaerobic members use sulfur as electron acceptor
instead of oxygen in cellular respiration.
 Some are lithotrophs that oxidizes sulfur to sulfururic
acid as an energy source.
 Such organisms require a very low pH and hence
known as thermoacidophiles.
 Inhabits regions associated with volcanic eruption viz;
hot, sulfur rich, acidic regions such as hot springs,
natural geysers, fumaroles etc .

15. HABITATS OF EXTREMOPHILES
Hot spring situated in Atlanta, USA
Courtsey:
http://www.idahohotsprings.com/destinations/atlanta/atlanta_hot_
springs_01.jpg

16. Castle Geyser, Yellowstone National Park, USA
Courtesy:
http://upload.wikimedia.org/wikipedia/commons/4/49/Steam_Phase_eru
ption_of_Castle_geyser_with_double_rainbow.jpg

17. Black smoker at a mid-ocean ridge
hydrothermal vent

18. Thermoacidophiles
 Requires both high temperature and highly acidic environment
for optimum growth.
 Preferred temperature range is 70-800
C and have an optimum
pH range of 2-3.
 All the organisms discovered belongs to the Domain Archae,
so far.
 They can thrive in acidous and sulfur rich environments.
 Instead of cell wall, possesses a unique membrane composed
of tetraether lipoglycan, which gives the unusual stability for
the bacteria.
 Eg: Thermoplasma acidophilum and T.volcanium

19. Facultative Thermophiles
 Rare group of organisms that can live both in higher
temperature and normal temperature are referred to
as facultative thermophiles.
 These organisms can live at 200
C, and have an
optimum of 500
C. Maximum temperature that they
can survive is 600
C.
 Eg: Bacillus flavothermus

20. ACIDOPHILES
 Microorganisms that lives in highly acidic
environments are called as acidophiles.
 The pH range is 1-5.
 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 eliminate protons from the
cytoplasm of the cell to maintain low pH.
 Eg: Pyrodictium, Picrophilus, Ferroplasma,
Sulfolobus

21. ALKALIPHILES
 These are extremophilic microorganisms which thrives
in roughly alkaline environments (8-11), and have an
optimum of pH around 10.
 Organisms which needs high pH to survive are called
as obligate alkaliphiles.
 There are facultative alkaliphiles and haloalkaliphiles
(needs salty environment as well).
 Most of the alkaliphiles possess a bacillus morphology.
 Eg: Bacillus halodurans C125,
Bacillus firmus OF4

22.  Two methods for surviving
1. The cell will be having a unique cellular
machinery that works best in alkaline range of
pH.
2. The cell will have to acidify the cytosol to nullify
the effect of the high pH outside the cell.

23.  Experimental studies revealed that the cytosolic
enzymes of alkaliphiles functions best in a neutral
pH range (7.5-8.5).
 This shows that for surviving in highly alkaline pH,
the cell must have some pH regulatory mechanism
to protect the plasma membrane.
 The mechanism is that the cell wall contains acidic
polymers composed of residues such as
galacturonic acid, gluconic acid, glutamic acid,
aspartic acid, and phosphoric acid.
 This protects the PM by preventing the entry of
hydroxide ions and allowing the entry of sodium
(Na+
) and hydronium ions(H+)

24. XEROPHILES
 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

25. HALOPHILES
 This group comprises microorganisms that can thrive in
high salty environments such as The Great Salt Lake
and Dead Sea.
 Most of the halophiles belong to the Domain Archae.
 Eg: Salinibacter ruber
 There are eukaryotic halophiles such as Dunaliella
salina (algae) and Wallemia icthyophaga (fungus).
 Extreme halophiles/obligate halophiles-adapted to
survive high salt concentrations
 Organisms from Dead Sea often requires nearly 33%
salt (sea water has only 3%), and the inoculating loop
must be dipped in a saturated salt solution to isolate
them.
 Microorganisms live in such high salinity are termed as
extreme halophiles

26. Mechanism
Mainly employ two mechanism to prevent desiccation
through osmosis.
Both strategies work by increasing the osmotic
concentration of the cell.
1.In first method (followed my most halophiles including
bacteria, archae etc) organic compounds are accumulated
in the cytoplasm.
They are known as osmoprotectants or compatible
solutes.
It include sugars, aminoacids, polyols, betaines etc.
These compounds can be synthesised or accumulated
from the environment.
Eg: Ectothiorhodospira halochloris

27. 2. The second is the selective influx of potassium
ions (K+
) into the cytoplasm.
 This adaptation is restricted to moderately
halophilic organisms.
 The entire intracellular machinery (enzymes,
structural proteins etc) is highly adapted to
withstand the high saline environment.
 Eg: Bacteria comes under the Family
Halobacteriaceae
 The 16S rRNA studies opens a broad range of
information on the field of evolution.

28. 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.

29. Characteristics
 Endoliths have been found in rocks down to the depth of
3 km.
 It is not known that whether this is the limit since digging
to the deep is highly expensive.
 The major threats to live in such depth is the high
temperature.
 Recently discovered strains can reproduce at 1210
C.
 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).

30. Endoliths can be classified into
 Chasmoendoliths
Colonizes fissures and cracks in the rock (chasmo-
cleft)
 Cryptoendolith
Colonizes structural cavities within porous rocks,
including spaces produced and vacated by
euendoliths (crypto = hidden)
 Euendolith
Penetrates actively into the interior of rocks forming
tunnels that conform with the shape of its body(eu =
good, true).

31. Endolithic life form found inside an Antarctic rock
http://en.wikipedia.org/wiki/File:Cryptoendolith.jpghttp://
en.wikipedia.org/wiki/File:Cryptoendolith.jpg

32. 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

33. An anaerobic work chamber and incubator
Fig: 6.15 page no:129, Prescott, Harley and Klein’s
microbiology

34.  To routinely grow and maintain in pure cultures,
reducing media which stored in ordinary, tightly packed
tubes is been used.( media containing thioglycollate
or cystein)
 For culturing in petriplates, sealed boxes and jars in
which oxygen removed completely is been used.
 Sometimes, certain chemicals which can produce
hydrogen and carbon di oxide will be added and the so
formed hydrogen will be incorporated with the oxygen
present in the container to yield water
 This water can be utilized by the microorganisms.
 The most advanced system is that the media used for
culture will be containing an enzyme- oxyrase which will
bind with oxygen and eliminate as water. No addition of
extra chemicals or hydrogen is needed.

35. Radiation
 Although most living things are sensitive to radiation,
there are some microorganisms which can resist high
levels of 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.
 They can survive exposure to radiation doses as high as
15,000 Grays. This much radiation is 1500 times the
dosage that would kill a human.
 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.

36. Barophiles
 Microorganisms that can survive under immense hydrostatic
pressure.
 Generally found in ocean floors where pressure exceeds
300 atm (38 MPa).
 Some have been found at the bottom of the Pacific Ocean
(Mariana Trench-10500 m) where pressure often exceeds
117 MPa.
 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 archae such as Pyrococcus spp.,
Methanococcus jannaschii are barophiles too.

37. SOME INTERESTING FACTS
 Halomonas titanicae- the bacterium which is
responsible for rusting of RMS Titanic.
 Pseudomonas putida (super bug) is a genetically
engineered bacteria which literally “eats” petroleum
products. These are very much useful in oil spills.
 GFAJ-1 is a strain of rod shaped bacteria in the
family Halomonadaceae which is an extremophile,
highly resistant to the dangerous poison-Arsenic.
 There are chances of life forms beyond earth and the
field of study is known as astrobiology.

38. ASTROBIOLOGY/EXOBIOLOGY

39.  The study of origin, evolution, distribution, and
future of life in the universe and life forms that are
extraterrestrial.
 Astrobiology arises a question whether life exists
beyond Earth and if so, how it can be detected by
humans.
 Nucleic acids might not be the only biomolecules
which codes for life.
 Astrobiology makes use
of physics, chemistry, astronomy, biology, molecula
r biology, ecology, planetary science, geography,
and geology to investigate the possibility of life on
other worlds and help recognize biosphere that
might be different from the biosphere on Earth.

40.  Recent advances in planetary science have
changed fundamental assumptions about the
possibility of life in the universe, raising the
estimates of habitable zones around other stars
and the search for extraterrestrial microbial life.
 The possibility that viruses might also exist
extraterrestrially has been proposed. Efforts to
discover life on Mars, either currently or in the past,
is an active area of research.
 Europa has emerged as one of the top locations in
the Solar System in terms of potential
habitability and the possibility of
hosting extraterrestrial life due to the presence of
liquid water (somewhat an ocean).

41. REFERENCES
 Precott, Haarley and Kleins Microbiology by Willey,
Sherwood and Woolverton. (5th and 8th editions)
 Microbiology - An Introduction (11th Ed)(gnv64)
Tortora
 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC98
975/
 http://library.thinkquest.org/CR0212089/therm.ht
m
 http://www.mhhe.com/biosci/genbio/raven6b/gra
phics/raven06b/enhancementchapters/raven30_
enhancement.html
 http://www.mapoflife.org/topics/topic_354_Extre
mophiles-Archaea-and-Bacteria/