Definition of Archaea (Archaea/Archaeabacteria)

Archaebacteria (as they are also often called) are a group of organisms with a very ancient evolutionary history and complex and difficult to trace because, like bacteria, they have the ability to transfer genes from one species to another. other. They have a great metabolic diversity that allows them to thrive in very nutrient-poor environments, since they are able to obtain energy from organic compounds. and inorganic under aerobic and anaerobic conditions, although this can also be seen in bacteria, there are specific processes that are unique to bacteria. archaebacteria. They stand out for having extremophile representatives, species that grow at temperatures above 80ºC, in acid environments, very saline or subject to high hydrostatic pressure.

in the big diversity biology of the planet there is a group of microorganisms that have been controversial since their discovery, since they share many similarities with the bacteria and with eukaryotic cells, however, they are separated from these two by molecular peculiarities in their membrane, in addition that they are an example of extraordinary adaptation to successfully survive in extreme environments where no other living being could. These are the archaea o

Archaea.

Structure and main characteristics of the Archaea

The configuration of the plasma membrane of the Archaea is a particular characteristic of this group of organisms, while in the domains Bacterium and eukarya, this is composed of phospholipids linked together by an ester bond, in the Archaea molecules of lipids Composed of a glycerol and isoprene linked together by ether-type bonds between the glycerol and the side chains, while in the other groups they do so by one of the ester type. This distinctive composition gives the Archaea a significant resistance to heat, allowing some species to grow at temperatures of more than 80ºC

Like bacteria, Archaea they have a wall cell phone, which in this case is a paracrystalline surface layer also known as the S layer, made up of glycoproteins that they intertwine forming hexagonal, tetragonal or trimeric symmetries, according to the subunits that compose it.

A distinctive aspect of the Archaea is that they also have an external membrane that is very diverse among the known species of this group, since they can contain different proportions of polysaccharides, proteins and glycoproteins depending on the environment to which they are adapted. For example, the methanogenic Archaea have a cell wall composed of a type of molecule much like the peptidoglycan found in bacteria, called pseudomurein. Pseudomurein is formed by several units of N-acetylglucosamine and N-acetylosaminuronic acid that are joined by glycosidic bonds between the sugars that compose them. On the other hand, the Archaea of the genre Methanosarcina they have a wall made of polymers of glucose, glucuronic acid, uronic acid, and acetate; while the Archaea that inhabit extreme salty ponds or seas such as halococcus have a cell wall with sulfate ions (SO₄^2-) that bind to Na⁺ to remain stable in this kind of environment.

Regarding the organization of their genetic material, like bacteria, Archaea they have a single circular chromosome and the ability to perform horizontal gene transfer via plasmids.

Classification and examples of its diversity

Through the analysis of the ribosomal sequences of the Archaea, in general there are five main phyla of this domain, whose main characteristics will be described below:

Euryarchaeota: In this group it is distinguished by the inclusion of methane-producing species (Methanobacterium, methanocaldococcus, Methanosarcina) and others that can live in very salty environments (Halobacterium, Haloferax, Natronobacterium), groups that are very contrasting with each other, since the former are strict anaerobes while the latter are strict aerobics; hyperthermophilic species are also included, that is, they resist high temperatures such as thermococcus and pyrococcus.

Thaumarchaeota: In this group there are species that inhabit the soils of the world whose contribution is nitrification as well as bacteria with the same function, with the difference that the archaea of ​​this group are adapted to extreme conditions of limitation of nutrients. Some genres in this group are: Nitrosopumilus and Nitrososphaera.

Nanoarchaeota: Phylum represented by a single and rare species, Nanarchaeum equitans, one of the smallest known organisms, with a volume that represents only 1% of Escherichia coli. This organism lives attached to Ignococcus hosptialis, another archaea, thus being the only known case of symbiosis in the entire domain Archaea.

Korarchaeota: The only characterized species of this phylum, Korarchaeum cryptophyllum It inhabits hydrothermal springs, whose metabolic characteristics are still being studied based on the sequence of its genome. Until now it is known that it ferments peptides.

Crenarchaeota: In this group are the most extreme species, since they are those that live in places with temperatures of up to 100º C and feed of inorganic substances, since in general, they have been found in hydrothermal vents on the ocean floor and in terrestrial volcanic habitats. Some genera of this phylum are: Sulfolobus, Acidus, thermoproteus, Pyrobaculum, Pyrodictium, ignicococus, staphylothermus.

References

Madigan, T., Martinko, J. M., Bender, K. S., Buckley, D. h. & Stahl, D. TO. (2015). BROCK. Biology of microorganisms. Pearson Education, S.A.