Archaebacteria Definition, Types, Characteristics, Structure, Examples

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Archaebacteria definition

  • Archaea form a part of a family composed of unicellulated organisms. 
  • They lack cell nuclei and thus are prokaryotes.
  •  Archaea were originally classified as bacteriaand were given the term archaebacteria (in the archaebacteria kingdom) However, this name has since been removed from use.
  • Archaeal cells are unique in their properties which distinguish them from other two domainsof the phylum, Bacteria as well as Eukaryota. 
  • Archaea are further subdivided into a variety of recognized classes of phyla.
  • It is difficult to classify because the majority are not isolated in a lab and are only recognized by the sequences of their genes in the samples from the environment.
  • Archaebacteria is a kind of single-cell organism that is distinct from other contemporary life forms that they have changed the way scientists categorize life.
  • However, biochemical and genetic research on bacteria quickly revealed that a particular type of prokaryotes was quite distinct in comparison to “modern” bacteria as well as unlike all other modern life types. Then, they were identified as “archaebacteria” because of “archae” meaning “ancient,” these unique cells are believed to be modern-day descendants of an extremely ancient lineage of bacteria that developed in deep-sea vents that were sulfur rich.
  • Advanced biochemical and genetic analysis has resulted in a brand novel “phylogenetic tree of life” which uses the notion of “domains” to define different divisions of life larger and more fundamental than “kingdom.”
  • The most recent variant of this method reveals all eukaryotes – species of fungi, plants, animals and protists. They form”Eukaryota,” the realm of “Eukaryota,” while the modern and more prevalent division of bacteria is “Prokarya,” and archaebacteria are their own distinct domain that is called “Archaea.”
  • It is the discovery that Archaea and its distinctive characteristics is exciting for scientists since it is believed that archaebacteria’s unique biochemistry could provide us with insights into the inner workings of the very early life. Certain scientists suggest that archaebacteria Thermoplasma could actually be the ancestral nuclei in our Eukaryotic cells. They may have evolved through endosymbiosis.
  • A unique characteristic of archaebacteria is their capacity to withstand extreme conditions which include very acidic, salty, and extremely hot environments. Archaebacteria have survived temperatures that reach 190 degrees Fahrenheit, which is just 22 degrees less than what is considered to be the water’s boiling point and acids that are as high as 0.9 pH.
  • Archaebacteria have even challenged scientists’ theories about what defines the term “species” because they are involved in a large amount of horizontal gene transfer. This is in which genes transfer from one person to another throughout their lives which makes it difficult to establish how closely cells are connected or whether archaebacteria cells exhibit the type of constant combinations of traits that scientists normally employ to define species.
  • The realm of Archaea includes both aerobic and anaerobic species. They can be found in normal environments like soil , as well as in extreme environments.

Archaebacteria characteristics

The following are the most important traits of archaebacteria.

  • Archaebacteria can be described as facultative or obligatory anaerobes i.e. they thrive even in absence of oxygen. this is the reason why they are able to undergo methanogenesis.
  • Cell membranes in Archaebacteria comprise lipids.
  • The cell’s wall is rigid and provides shape and stability for the Archaebacteria. It also shields the cell from rupture under hypotonic conditions.
  • Cell wall made of Pseudomurein which shields archaebacteria against the effects of Lysozyme. Lysozyme is an enzyme produced from the body’s immune system that destroys in the cells wall that harbor pathogens.
  • They do not have organelles that are membrane bound, such as nuclei, endoplasmic-reticulum mitochondria, lysosomes, mitochondria, or chloroplast. The cytoplasm is thick and is filled with all the essential compounds to regulate metabolism and nutrition.
  • They can be found in various conditions and hence are known as extremophiles. They can live in acidic and alkaline water areas, and at temperatures that are above the boiling point.
  • They are able to stand up to extremely high pressure of over 200 atmospheres.
  • Archaebacteria do not react to major antibiotics since they possess antimicrobial resistant plasmids. enzymes.
  • The way of reproduction is sexual, called binary fission.
  • They are able to perform gene transcription that is unique.
  • The distinct the ribosomal RNA suggests the possibility that they differed from prokaryotes as well as eukaryotes.

A. Types of archaebacteria based on Habitat

Archaebacteria are classified based on their phylogenetic connection. The archaebacteria that are the most prevalent are described in the following sections:

1. Crenarchaeota

  • Crenarchaeota are Archaea that are found across a wide range of habitats.
  • They can withstand extreme temperatures or extreme heat.
  • They contain specific proteins that allow to perform at temperatures up to 300 degrees Celsius.
  • They are located in deep-sea vents , as well as hot springs, which are regions that have superheated waters.
  • They include hyperthermophiles, thermophiles as well as thermoacidophiles.
  • The word Crenarchaeota translates to “scalloped archaea.” They’re usually odd in their shape.
  • Crenarchaeotes all synthesize a distinct triether lipid called crenarchaeol.
  • Originally, the spores contained hyperthermophilic and thermophylic sulfur that metabolizes archaea.
  • Recently discovered Crenarchaeota have been inhibited by sulfur, and they grow best when temperatures are lower.
  • They stain Gram negative and are morphologically diverse , with filamentous, cocci, rod and strangely shape cells
  • Example:
    • One of the most well-studied species of Crenarcheota includes Sulfolobus solfataricus, which was isolated from the sulfuric hot springs geothermally heated in Italy and grows at 80°C and pH ranging from 2-4.
    • Other Examples can be found in Pyrolobus fumarii.
    • Sulfolobus solfataricus as well as Sulfolobus acidocaldarius

2. Euryarchaeota

  • They can withstand extreme alkaline conditions, and they have the capacity to create methane in a way that is different from any other living thing on the planet. They include methanogens and halophiles.
  • Highly diverse with 7 classes. Methanococcus, Methanobacteria, Halobacteria, Thermoplasmata, Thermococci, Archaeglobi & Methanopyri.
  • It is comprised of 9 orders and 15 families.
  • Based on their habitat, they are classified into methanogens extreme halos, sulphate reducers, and numerous extreme thermophiles having S-dependent metabolism.

3. Korarchaeota

  • They have the same genetics with Crenarchaeota as well as Euryarchaeota.
  • They are all believed to descend from the same ancestor.
  • They are believed as the oldest organisms on the planet.
  • They include hyperthermophiles.
  • The name comes by it being derived from the Greek noun koros, or Kore, which means ”young person or young woman”, and an Greek adjective archaios that refers to “ancient”. The are sometimes referred to as Xenarchaeota.
  • The Korarchaeota are only found in hydrothermal environments with high temperatures.
  • The area of Yellowstone National Park (YNP), Korarchaeota were most abundant in springs, with an pH range from 5.7 through 7.0.
  • Korarchaeota Korarchaeota were first discovered through the analysis of microbial communities of ribosomal DNA genes taken from the environment of hot springs in Yellowstone National Park.

4. Thaumarchaeota

  • This includes archaea, which can oxidize ammonia.
  • Thaumarchaeota Thaumarchaeota (from the Greek “thaumas” which means wonder) was introduced in 2008 following C.symbiosum’s genome C.symbiosum was sequenced, and it was found to differ in significant ways from other members of the phylum Crenarchaeota.
  • All organisms of this lineage thus far identified are chemolithoautotrophic ammonia-oxidizers and may play important roles in biogeochemical cycles, such as the nitrogen cycle and the carbon cycle.
  • It was promoted on the evidence from phylogenetics including the sequences of the ribosomal RNA of these organisms’ genes, as well as the existence of a topoisomerase type I that was previously believed to be exclusive to Eukaryotes.
  • Examples: Nitrososphaera viennensis

5. Nanoarchaeota

  • The symbiont is only obligate from archaea that belongs to the Ignicoccus genus.
  • In taxonomy, we have the Nanoarchaeota originates from Greek is a reference to “old dwarf”.
  • They live in high-temperature environments, that allow for optimum growth at 90 C and are uncommon because they grow and split off within the shell of an archaea called Ignicoccus.
  • Nanoarchaea was identified in the year 2002 are the tiniest living cells (1/100th that of Escherichia coli) and the tiniest known genome (480 Kilobases [1 Kilobase = 1,000 base pair of DNA] ).
  • Members belonging to this phyla aren’t identified in pure cultures.
  • The cells of Nanoarchaeum are approximately 0.4 millimeters wide and only reproduce when connected on the outside of Ignicoccus.

B. Types of archaebacteria based on Nutrition

Although some archaebacteria are heterotrophic, the majority are chemoautotrophs. That is, they create their own food using substances found in their environment. Based on the method that they consume their nutrition (metabolism mechanism) archaebacteria are divided into four categories including methanogens and halophiles, sulfur reducersand thermoacidophiles.


1. Methanogens

  • Methanogens are anaerobic. They feed on decaying plant matter and other organic matter, creating methane gas and water.
  • They are located in marshes and bogs deep within oceans, and also in the digestive tracks of herbivores with cellulose fermentation that assist in the digestion process of the cellulose.
  • Certain methanogens thrive near volcanic vents. The capacity of these bacteria to live close to vents like these is an area of great interest for scientists, as the water in these regions can reach temperatures as high as 120 degrees Celsius.
  • The majority of organisms aren’t able to stand up to the conditions. Proteins change shape and cease to function approximately 45 ° Celsius. The way in which methanogens have adapted the extreme temperatures is not yet understood.
  • Examples:  Methanofollis aquaemaris, M. ethanolicus, M. formosanus, M. liminatans

2. Halophiles

  • The Halophiles, also known as phototrophs (producing their energy through light) that utilize a violet version of chlorophyll known as bacteriorhodosin.
  • They reside in extremely salty environments, like those within the Great Salt Lake and the Dead Sea.
  • These environments pose two problems. The first is that the difference in salt concentration within and outside of the cell is huge, which creates massive osmotic pressure. While other organisms could quickly shed all their water and eventually die but halophiles have developed the ability to live with this different water gradient. Additionally, the environments that are salty are extremely alkaline, with certain having pHs of upwards of 11.5. In addition to surviving in these hostile environments, halophiles have integrated the conditions in their unique photosynthetic pathway. A majority of halophiles are Aerobes.
  • Example: Halobacterium which includes several species, found in salt lakes & high saline ocean environments.  Halobacterium salinarum,  H. denitrificans &  H. halobium.

3. Sulfur Reducers

  • Similar to methanogens sulfur reducers are found close to volcanic vents and lakes.
  • The name of the vent suggests that they rely on the abundance of sulfur inorganic found in these vents, as well as hydrogen as food sources.
  • They also have extremely high tolerance to heat, living in temperatures as high as 85 ° Celsius.
  • Their Class is Archaeglobi and their order is Archaeoglobales.
  • It is Gram -ve irregular coccoid cells.
  • Cell wall is composed by glycoproteins subunits.
  • Their electron sources include hydrogen, lactate, and glucose. They reduce sulfate, the sulfite or thiosulfate form sulf.
  • The S symbol isn’t used to act as an electron acceptor.
  • Extremely thermophilic, Optimal temperature is around 83 C can be found in hydrothermal vents 

4. Thermoacidophiles

  • Thermacidophiles are also dependent on sulfur, however they do this by oxidizing itand combining sulfur with oxygen molecules instead of hydrogen.
  • As with the methanogens as well as sulfur reduction agents, the archaebacteria reside near volcanic vents and lakes and, consequently, are adapted for extreme temperature (65 up to 80° Celsius).
  • In contrast to the other two classes however, thermoacidophiles require extremely acidic conditions, and can be found in conditions with pH of as lower as 1.0.
  • Nearly all thermoacidophiles are anaerobes.
  • Example: Pyrolobus fumarii, currently holds the record for high- temperature growth, it can grown in temperatures up to 113oC.

Morphology of Archaebacteria

  • Archaea vary in size between 0.1 millimeters (mm) to more than 15 millimeters in size, and are found in many shapes, most commonly as rods, spheres, plates or spirals.
  • Other morphologies of the Crenarchaeota include lobed irregularly-shaped cells in Sulfolobus needle-like filaments which are smaller than half a micrometer across in Thermofilum and near-perfectly round rods from Thermoproteus as well as Pyrobaculum.
  • Archaea from the genus Haloquadratum like Haloquadratum Walsbyi are flat square species that reside in hypersaline pools.These strange shapes are most likely preserved by their cell walls as well as an cytoskeleton that is prokaryotic.
  • Proteins that are akin to the cytoskeleton components of different organisms are present in archaea and filaments develop inside their cells. However, unlike other species, the structures of their cells are not well understood.
  • For Thermoplasma or Ferroplasma the absence of a cell’s wall signifies that cells are irregular in forms, and may resemble amoebae.
  • Certain species form aggregates and filaments that can be that are up to 200 millimeters in length. They can be found in biofilms.
  • Notably, the aggregates made up of Thermococcus coalescens cells meld when they are in the culture, and form huge cells.
  • Archaea within the genus Pyrodictium create a complex multicell colony with a variety of thin, long tubes, called cannulae, that extend from the cells’ surface and connect them to form an agglomeration that resembles a bush. The purpose of these cannulae are not established, but they might facilitate communication or exchange of nutrients with neighbours.
  • There are multi-species colonies like for instance the “string-of-pearls” community, which was first discovered in 2001 in the German swamp.
  • The round, whitish colonies of the unique Euryarchaeota species are arranged by thin filaments that be between 15 centimetres (5.9 in) long. The filaments are produced by one specific species of bacteria.

Structure of Archaebacteria

Archaea and bacteria generally have similar cell structures, but the composition of cells and their organization sets them apart. Similar to bacteria, archaea have no organelles inside their membranes. Similar to bacteria, the cell membranes of archaea typically bounded by a cell wall, and they swim with several flagella. The structurally, archaea is most like Gram-positive bacteria. They possess only a single plasma membrane as well as a cell wall, but do not have an periplasmic area; the exception to this principle is Ignicoccus and Ignicoccus, which have an especially large periplasm which has membrane-bound vesicles, and is protected with an external membrane.

Structure of Cell wall

  • The majority of archaea (but not Thermoplasma and Ferroplasma) contain the cell wall.
  • In the majority of archaea, walls, the wall is made of proteins that make up the surface layer, which forms an S-layer.
  • The S-layer is sturdier collection of protein molecules that covers the exterior of cells (like chain mail).
  • This layer offers physical and chemical protection and also prevents macromolecules from touching to the membrane of cells.
  • As opposed to bacteria, archaea do not have peptidoglycans in their cell walls.
  • Methanobacteriales do have cell walls containing pseudopeptidoglycan, which resembles eubacterial peptidoglycan in morphology, function, and physical structure, but pseudopeptidoglycan is distinct in chemical structure; it lacks D-amino acids and N-acetylmuramic acid, substituting the latter with N-Acetyltalosaminuronic acid.

Structure of Archaeal flagella or archaella

  • Archaeal flagella are also known as archaella. They operate as bacterial flagella. Their long stalks are powered by motors that rotate at the base.
  • They run on a gradient of proton over the membrane. However, archaella are distinct in the composition and growth.
  • The two kinds of flagella evolved from various ancestral lineages.
  • The flagellum of a bacterium shares an ancestor common to the secretion system of type III, the archaeal flagella seem to be derived from bacterial pili type IV.
  • In contrast to the flagellum of bacteria which is hollow and is assembled through subunits that travel through the central pore until the point of the flagella. Archaeal flagellas are made by adding subunits at the base.

Structure of Membranes

The archaeal membranes consist by molecules distinct from those found in all other life forms, which indicates that archaea can be compared in a limited way to eukaryotes and bacteria. Cell membranes are composed of phospholipids or phospholipids. They have an polar component which dissolves when water is added (the”head” of phosphate) “head”) as well as the “greasy” non-polar component which does not (the tail of lipids). The two parts are linked via a glycerol component. Within water, phospholipids form a cluster with their heads facing water, and the tails towards it. The primary structure of cell membranes is that of a two-layer of the phospholipids. It is referred to as a lipid bilayer.

The archaean phospholipids are unique for four reasons:

  1. Membranes of these species are made up of glycerol ether lipids. bacteria and eukaryotes’ membranes consist predominantly of glycerol-ester-based and glycerol-ester. The distinction lies in the kind of bond that connects the lipids and the glycerol moiety. two types are depicted by the color yellow in the illustration below. In ester lipids it can be described as an ester bond however, in ether lipids it bonds to an ether.
  2. Stereochemistry in the archaeal Glycerol moiety is mirror-image seen in the other species. Glycerol moiety is found with two distinct forms which mirror images of each other known as Enantiomers. As a right-handed hand cannot easily fit to a left-handed glove the enantiomers of a particular type typically aren’t made by enzymes that are adapted to the different. The archaeal phospholipids are built on a backbone of sn-glycerol-1-phosphate, which is an enantiomer of sn-glycerol-3-phosphate, the phospholipid backbone found in bacteria and eukaryotes. It is believed that archaea utilize completely different enzymes to synthesize the phospholipids, as opposed to eukaryotes and bacteria. The enzymes that archaea use developed at earliest in the evolution of life, suggesting an early separation from the two other domains.
  3. The Archaeal lipid tails are different from other organisms due to the fact that they are built on long chains of isoprenoid with many side-branches, and sometimes rings of cyclopropane and cyclohexane rings. Contrary to this the fatty acids found in Membranes of various organisms are straight chains that lack side rings or branches. Although isoprenoids play an essential part for biochemistry in a variety of species, only archaea make them for phospholipids. These chains can aid in preventing archaeal membranes from leakage at temperatures that are high.
  4. In some archaeas in some archaea, the bilayer of lipids is replaced by the monolayer. In essence, the archaea join their tails from two different phospholipids to create an molecule that is a single one with two heads with polarity (a Bolaamphiphile) and this may create membranes that are more rigid and better equipped to withstand harsh environments. For instance the lipids found in Ferroplasma have this kind and are believed to help the organism’s survival in its acidic environment.

Examples of Archaebacteria

1. Lokiarcheota

Lokiarcheota is an hyperthermophile found in deep-sea vent known as Loki’s Castle, which some scientists believe has a unique genetic significance.

It is a truly unique genome that is comprised of 26% proteins recognized to be present in other archaebacteria. There are 29% proteins identified in bacteria and 32 percent of genes that don’t match any protein known to exist as well as – 3.3 percentage of genes that match to proteins only found in the eukaryotes.

The eukaryotic genes are especially interesting for researchers, as they are the genes that may encode proteins that eukaryotes employ to regulate the shape of their cells and cytoskeletons, which include proteins and Actin is the principal motor component and a variety of proteins that in the eukaryotes participate in altering cell membranes’ shape.

A few of these genes play a role in phagocytosis. This is interesting because the process of the phagocytosis process could have been employed by our ancestors from the eukaryotic lineage for “swallow” different cells. These could be able to develop into endosymbiotes. This could have led to endosymbiotic relations between eukaryotic cells, the mitochondria of their chloroplasts and nuclei.

Lokiarchaeota’s distinctive genome is likely to be our closest to prokaryotes. It is also could be a transitional species in the crucial transition from prokaryotic life to eukaryotic that made the development of the plants, animals and protist kingdoms feasible. Researchers believe that Lokiarchaeota and us may have shared a common ancestral lineage around 2 billion years ago.

It’s not known if this implies that eukaryotes may have developed around deep sea vents or if Lokiarchaeota’s cousins could previously have been prevalent in other environments prior to when they were pushed out of competition and forced to the brink of extinction by their advanced eukaryotes, their more advanced cousins.

2. Methanobrevibacter Smithii

Methanobrevibacter Smithii is a methane-producing archaebacteria which lives within the human digestive. This part of Euryarchaeota assists us in breaking down complex sugars in plants and to extract additional energy from food items we consume.

The microorganisms we have in our gut – and this includes the members of Euryarchaeota also have an intricate relationship with our health. Although some studies have shown that many obese people or colon cancer carry higher concentrations of Euryarchaeota in their digestive tracts, Euryarchaeota also help people who aren’t eating enough to make more energy and certain kinds of archaebacteria may protect us from colon cancer.

Importance of Archaebacteria

The importance of archaebacteria may be understood by examining the following aspects:

  • The Archaebacteria species have forced scientists to reconsider the traditional concept of species. The term “species” refers to a group of organisms that have gene flow among its members. The archaebacteria show gene flow throughout its species.
  • Methanogens are utilized to produce methane, which is an abundant source of energy.
  • Exthermophilic Archae Resilient to either heat or extremes in acidity and alkalinity. They are utilized for various reasons, such as: Thermostable DNA polymerases like (a) Pfu DNA polymerase. Pfu DNA polymerase of Pyrococcus furiosus, are utilized in PCR. (b) Amylases as well as galactosidases and pullulanases from various species of Pyrococcus which function at more than 100 degrees Celsius, allow food processing at a high temperatures.
  • Preparation of glycoproteins and proteins from archaeal species help to strengthen the your body’s immunity against infection.
  • Halophilic archaea can be utilized to help prescreen antitumor medications which are active against eukaryotic protein
  • They perform anaerobic digestion that produces biogas.
  • Thermophilic archaea is used in PCR.
  • These (Acidophilic Archae) are used for the extraction of metals like cobalt, copper, and gold from their ore.
  • Play important role in carbon cycle,nitrogen cycle, sulphur cycle etc.
  • They aid in research for example; their capacity to endure extreme conditions aids researchers understand the environment, climatic conditions and the way they survived on earth.
  • Archaea hosts a new class of antibiotics that may prove useful.

Facts About Archaebacteria

  • They are found in extreme environments (like hot salty lakes or hot springs) as well as normal conditions (like the ocean and soil).
  • All cells are unicellular (each person has only 1 cell).
  • There isn’t any peptidoglycans in the cell walls.
  • A few have a flagella that helps them move.
  • Many don’t require oxygen to live.
  • They are able to create ATP (energy) through sunlight.
  • They are able to withstand extreme temperatures.
  • They can live under rock and even in ocean floor vents which are located deep beneath the surface of the ocean.
  • They can withstand massive pressure differentials


  • Dunlap, Paul V. (2001). Encyclopedia of Biodiversity || Microbial Diversity. , (), 280–291. doi:10.1016/B978-0-12-384719-5.00435-4 
  • C. R. Woese; L. J. Magrum; G. E. Fox (1978). Archaebacteria. , 11(3), 245–252. doi:10.1007/bf01734485 
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