Definition: What are Archaea?

Archaea are unicellular organisms that make up the third doprimary of organisms on earth. Therefore, they are different from the other 2 domains that include Bacteria and also Eukaryota.

Like bacteria, yet, archaea are prokaryotes that share specific features with bacteria (this is among the factors archaea were formerly thshould be a type of bacteria).

Due to their ability to survive extreme conditions, they have the right to be uncovered in a variety of environments varying from lakes and soil to the Dead Sea and the deepest parts of the ocean (sea floor).

Some examples include:


Aeropyrum pernixThermosphaera aggregansIgnisphaera aggregansSulfolobus tokodaiiMetallosphaera sedulaStaphylothermus marinusThermoproteus tenax


Archaea by Kaden11a

Based on miscellaneous molecular and also genetic compositions, the domain Archaea is subsplit right into 5 (5) phyla that include:


Phylum Euryarchaeota

The phylum Euryarchaeota is among the best-studied phyla of the domain (Archaea). Consisting of more than 70 genera, members of the phylum are exceptionally physiologically varied through the capacity to endure some of the most too much settings roughly the civilization.

The complying with are attributes of different groups of the phylum Euryarchaeota:


Euryarchaeotae is created of mesophilic, thermophilic and psychrotolerant species spreview throughout eight (8) classes. 


Class Archaeoglobi - The class Archaeoglobi is consisted of of a solitary order (Archaeoglobales) and family (Archaeoglobaceae). Archaeoglobaceae is even more separated right into 3 genera that incorporate Ferroglobus, Geoglobus, and also Archaeoglobus. Like course Thermococci, members of Archaeoglobi are spherical in appearance and for this reason may be defined as having actually a coccoid morphology.

Some of the primary qualities of this group include:

They are discovered in hydrothermal vents (in deep-sea)AnaerobicThey grow well in marine salinityThe three genera in the phylum contain species that are mixotrophic (usage various sources of energy) and lithoautotrophic (achieve power from decreased compounds) in natureOptimum temperature range for members of this phylum is in between 83 and also 88 levels Celsius (maximum temperature is around 95 levels Celsius)


Class Protoarchaea - Also known as class Thermococci, Protoarchaea is additionally made up of a single order (Thermococcales) and also family members (Thermococcaceae). The household Thermococcaceae is better divided into the genera Pyrococcus, Thermococcus, and Paleococcus.

With the exemption of a few species, a bulk of species in these genera have the adhering to characteristics:

Hyperthermophilic (thrive in incredibly hot environments)OrganotrophicGrow well in neutral pH and also marine salinityCoccoid in morphologyCapable of movementFound in hydrothermal ventsSome species are capable of fermentationAre all obligate organo-heterotrophs (they deserve to acquire energy/nutrition from organic compounds or from other organisms)


Class Thermoplasmata - Class Thermoplasmata is consisted of one order (Thermoplasmatales) and also 3 family members.

Members of this course have the complying with characteristics:


Extreme acidophiles (flourish under acidic conditions)Aerobic in nature (they require air for growth)Spherical/coccoid morphologyMajority of species are moderate thermophiles (they prosper under modeprice temperatures- listed below 40°C)Some species (e.g. members of family members Ferroplasmaceae) can oxidize iron compounds to obtain energyThey are incapable of fermentation


Class Halobacteria - Consisting of about 30 genera, the Class Halobacteria is made up of organisms that are extremely halophilic in nature. Therefore, they are able to thrive well in settings via high salt concentrations (30 to 36 percent sodium chloride). For this factor, they deserve to be uncovered in such excessive environments as the Dead Sea.

Several of the various other crucial attributes of the members of this class include:

Aerobic organisms (require air for growth)Many of the species additionally need magnesium salts for their developmentMany of the species are pleomorphic in morphology which is caused by the high minerals in their environmentsA majority of the species are Gram-negative through just a couple of being Gram-variableMesophilicChemo-organotrophs - They oxidize the chemical bonds of complicated organic compounds (peptone etc) to obtain energyA majority of the species are discovered in such salty atmospheres as soda lakes and marine springs containing sulfur and also sulfide among others


Methanogens incorporate four classes of the Phylum Euryarchaeota that are characterized by their capability to produce methane. These encompass Methanotherma, Methanobacteria, Methanopyri, and also Methanomicrobia.

Acomponent from the capacity to develop methane, all members of this group are obligate anaerobes that use carbon dioxide to accept electrons. Therefore, they cannot tolerate the existence of oxygen.

Some of the other characteristics of Methanogens include:

Can be uncovered in the digestive device of ruminant animals (e.g. goats and also residential yak) - In the rumen of these animals, Methanogens are connected in the fermentation processAre discovered in the deep-sea and saline environments (e.g. members of Class Methanopyri and also Methanothermea)Vary from cocci and also curved rods to lengthy and also short in morphologyGrow well in neutral settings (or slightly alkaline environments)
Archaea by Themasterdidi

Phylum Crenarchaeota

Apart from the Phylum Euryarchaeotae, Phylum Crenarchaeota is the various other team of organisms that has obtained a lot of attention over the years.

Although this phylum includes fewer genera compared to the former, it consists of a great diversity of organisms that deserve to be discovered in various types of atmospheres. For instance, whereas some of the species have the right to be uncovered in the soil, others can be discovered in high-temperature settings (thermophiles).

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Compared to the phylum Euryarchaeotae, a solitary class (Crenarchaeota) of phylum Crenarchaeota has been determined so much.

Crenarchaeota is better separated into five orders that include:


Order Acidolobales - Members of this order are acidophiles that use sulhair throughout respiration (as the electron acceptor). They are spherical in shape (cocci) and also include members of 2 major households namely, Acidilobaceae and Caldispheraceae.

Order Desulfurococcales - This order is split into household Pyrodictiaceae and family Desulfurococcaceae. Whereas some are cocci in their morphology (the majority of Desulfurococcaceae), others are rod-shaped. 

Several of the various other attributes of Order Desulfurococcales include:

Some are obligate anaerobes in nature (Desulfurococcaceae)Slightly acidophilic or neutrophilic organisms that have the right to be found in some marine settings (Desulfurococcaceae)Some members are fermentersSome members of the household Pyrodictiaceae are thermophiles and deserve to survive very high temperaturesG+C content varies from one team to another


Order Sulfolobales - The Order Sulfolobales is composed of a single family members (Sulfolobaceae) which is in turn comprised of hyperthermophilic and also acidophilic organisms spreview across six genera.

Characteristics of the order Sulfolobaceae vary from one team of organisms to one more. For circumstances, whereas the genus Sulfurisphera is comprised of an organism that is strictly organotrophic facultative anaerobe, members of Acidianus and also Sulfolobus among others have been displayed to use lithoautotrophic and organotrophic metabolism.


Order Thermoproteales - This order is created of 2 households (Thermofilaceae and Thermoproteaceae) that have actually the following characteristics:


Neutrophiles or slightly acidophilic organisms that can be discovered in high-temperature atmospheres (hyperthermophiles)Rod-shapedSome are fermenters (Thermoproteus)Some deserve to flourish on compounds containing hydrogen and also thiosulfates etc


Order Fervidicoccales - This order consists of a single family members and species that deserve to be found in warm springs.



The other three phyla of Archaea are not completely understood and no valid representatives have actually been agreed on.

The adhering to are some of the attributes of the three groups:


Korarchaeota - This phylum was uncovered in both marine and terrestrial warm environments for this reason suggesting that members of the phylum are hyperthermophilic. In order to recognize the diversity and also abundance of the group in nature, research studies have actually been performed in assorted settings and in a variety of nations.

Thturbulent these studies, it ended up being apparent that members of the phylum prosper in atmospheres that array between 70 to 97 degrees Celsius in temperature, and also 2.5 and 6.5 in pH. Right now, incredibly few organisms have actually been established as belonging to the phylum. One instance of this is the Candidatus Korarchaeum cryptofilum that was isolated from a culture containing sediments from Obsidian Pool. 

Based on studies on the organism, the following attributes were identified:

Capable of degrading peptides through fermentationCannot synthedimension such co-factors as vitamins


Nanoarchaeota - Like the phylum Korarchaeota, just one member (Nanoarchaeum equitans) of phylum Nanoarchaeota has actually presently been figured out. 

N. equitans has actually been displayed to grow attached (in a symbiotic relationship) to the surface of assorted Ignicoccus species and has actually the complying with characteristics:


Hyperthermophilic organismsCan be uncovered on hot rocks, marine thermal vent atmospheres and also springsAre strict anaerobesContain divergent 16S rDNA sequenceLack genes responsible for the synthesis of lipid, amino acids, and nucleotideGrow well in high temperatures (around 90 degrees Celsius) and pH selection of in between 2.5 and 3.0


Thaumarchaeota - As compared to Korarchaeota and Nanoarchaeota, Thaumarchaeota is better construed via the team making up about five (5%) percent of all prokaryotes in soil devices. They can additionally be found in warm springs and also marine waters and consist of ammonia-oxidizing organisms. 

A few of the main attributes of Thaumarchaeota include:

A majority of the organisms deserve to fix carbon dioxide under autotrophic conditionsThey oxidize ammonia aerobically

Archaeal Groups

Acomponent from phylum divisions of Archaea, the doprimary is also split into the adhering to three groups:

Extreme Halophiles

Extreme halophiles include a variety of organisms that grow in an setting that contain high salt concentrations. For optimal expansion, extreme halophiles have been presented to require at least 1.5 mol l-1 of sodium chloride. As such, while many may tolerate high salt problems, a great number have been displayed to actually depfinish on such conditions for growth.


Instances of excessive halophiles include:




Methanogens are characterized by the inability to tolerate oxygen and the ability to create methane.

Methane gas is therefore developed under anaerobic problems and also in the absence of such ions as ferric ions and also nitrates. In cases wbelow methanogens live in anoxic soils or in atmospheres wright here other organisms create oxygen, they produce methane at a high price in order to carry about anoxic problems.

Due to the fact that of their capacity to create methane, they have been provided in some sectors to develop the gas.

Instances of methanogens include:


Methanopyrus kandleriMethanocaldococcusMethanobrevibacterMethanosphera


Hyperthermophiles are also typically described as heat-loving prokaryotes. This is because they are a group of Archaea that are capable of thriving in temperatures of over 80 degrees Celsius.

They are frequently found in settings with exceptionally high temperatures such as warm acid springs, in geothermal power plants and submarine volcanic habitats and areas through heated soil.

Acomponent from high temperatures, some Hyperthermophiles have additionally been shown to tolerate extreme acidity in their environments. However, the majority, which is obligate anaerobes, flourish well in settings that are either neutral or mildly acidic.

Examples of Hyperthermophiles include:



Main Characteristics of Archaea (Vs. Bacteria)

Because of their diversity, archaeal cells display considerable variance in morphology. Whereas some are rod-shaped, prefer many bacteria, others are spiral, disk shaped or spherical in form. On the other hand, some have been presented to portray assorted irconsistent shapes.

Although Archaea is a unique domain, it shares a variety of attributes with both Bacteria and Eukaryota. For circumstances, favor bacteria, a majority of archaea have a cell wall that regulates osmosis and also maintains the form of the cell.

However before, unlike bacteria, archaea execute not have the peptidoglycan. Rather, they contain pseudopeptidoglycan consisting of N-acetyltalosamine uronic acid (NAT) while others have actually a cell wall comprised of proteins or polysaccharides.

Both (bacteria and also archaea) are additionally capable of locoactivity in moist or liquid environments. This is made possible by the presence of flagella. Depfinishing on the species, archaea may possess a one or numerous flagella permitting it to move from one allude to another.

Although they both possess flagella that enable for locoactivity, the flagella protein and the framework of flagella is various in between the two.

The other distinction in between archaea and bacteria is with regards to their cell membrane. While both have actually a cell membrane, there is a difference in exactly how miscellaneous components of the cell membrane are arranged in archaea. For instance, in archaea, the tails of the hydrophobic lipid are attached to the glycerol by ether linkperiods. This is various from the ester link existing in Bacteria and also Eukaryota.

With both Bacteria and also Archaea being prokaryotes, the chromosome area is created of bodies well-known as nucleoids. Compared to Eukaryotes, these diffusage mass absence a membrane envelope and also therefore reside in the cytoplasm as DNA aggregateways.

Both Bacteria and also Archaea additionally contain plasmids (little DNA molecules). These extrachromosomal molecules of DNA are frequently circular in shape with genes varying from about 5 to 100.

* Like Eukaryotes, Bacteria and Archaea have actually also been shown to have actually a cytoskeleton that regulates cell division.

See more: What Does Living On The Edge Mean, On The Edge Definition & Meaning

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Elena V. Pikuta. (2014). Synopsis of Archaea. ResearchGate. 


Jeffrey C. (1994). Cell Structure and also Function in the Bacteria and Archaea. Fundamentals of Microbiology - Pommerville 9th Edition. 


Jet McLain. (2004). Archaea. Encyclopedia of Soils in the Environ., Elsevier Ltd., Oxford, UK, pp. 88-94, 2004..


Jose Berenguer. (2011). Thermophile. Encyclopedia of Astrobiology.