In terrestrial life you can find different types of domains , the eubacteria that are also called true bacteria, the eukaryotes where humans are located and finally the Archeas or Archae , where we find the archaebacteria . This last group can be observed under a microscope with characteristics similar to bacteria, however, they have very important differences between the two.

What are archaebacteria?

Archaebacteria are a special group formed by unicellular organisms that do not contain a nucleus and that also have membranous organelles in their internal part forming a separate Domain .

  • Definition
  • Characteristics of archaebacteria
  • Domain
  • Which kingdom do they belong to
  • Types of archaebacteria
  • Structure
  • Nutrition of archaebacteria
  • Habitat
  • Function
  • Diseases
  • How they differ from eubacteria
  • Importance
  • Examples of archaebacteria


The group of archaebacteria is one of the oldest that exists and thanks to its special characteristics they make up a completely separate Domain known as Archae . They are organisms very similar to eukaryotes in the aspect of not having a part of their cell membrane , which is known by the name of peptidoglycan. They are also similar to bacteria in that they do not have the genetic material inside a membrane but it is found throughout the cell. They are basically a mix between bacteria and eukaryotic organisms.

Characteristics of archaebacteria

Among the most outstanding characteristics that can be observed in archaebacteria, the following are mentioned:

  • They are considered the oldest organisms that exist on earth.
  • They measure approximately between 5 and 5 microns .
  • Its shape is stick, palm or spiril .
  • They do not contain the basic structure in the cell wall so they do not have peptidoglycan .
  • They are prokaryotic organisms and also reproduce asexually through spores .
  • They do not have nuclei, nor do they have organelles , lysosomes , endoplasmic reticles , or Golgi complexes .
  • They are capable of withstanding quite high temperatures , which is why they are considered hyperthermophilic .
  • They are anaerobic so they can only survive in places where there is no oxygen.
  • They have the ability to synthesize chemicals such as sulfur.


Its domain belongs to the Archae and is completely independent of eubacteria due to the great variety and phylogenetic differences. It has that name because it is considered to be the oldest in the world.

Which kingdom do they belong to

Archaebacteria are ancient organisms that have a prokaryotic morphology and are located in the Kingdom of Archaebacteria . This kingdom is subdivided into five phyla that have been recognized by experts, however this process is still under investigation.

Types of archaebacteria

Archaebacteria can be divided or grouped into three different groups mentioned below.

Methanogenic archeas

This first group is made up of all those archaebacteria that have the ability to produce methane . They can generally be found in places where there is no presence of oxygen, such as swamps, deep water, sewage, and they have sometimes been found in the stomachs of ruminants such as cows. They can obtain energy from carbon dioxide and hydrogen while releasing methane gas as a waste from metabolism.

Halophilic archeas

This type of archaebacteria is also known as extreme halophilic man . It is important to know, to understand the type, to know that halophilic means “who likes salt” . For this reason, halophilic ones can be found in places where there are high concentrations of salt, such as the Dead Sea. Some of them cannot tolerate low levels of this mineral. They use sunlight as a source of energy thanks to a pigment they have called bacteriorredopsin .

Thermoacidophilic Archeas

This last group of archaebacteria can be found inhabiting hot waters that are also acidic , such as those found in sulfur springs or in vents located at the bottom of the sea. They are also known as extreme thermophiles.


The structure of archaebacteria is characterized by being microscopic , they are unicellular and are also prokaryotes , which means that they only have one prokaryotic cell so they can only be seen under a microscope. They have a structure that has a cell membrane, cell wall, flagella, cytoplasm, ribosomes, plasmids, and DNA. 

Lipids can be found in its cell membrane, which makes them have a monolayer to withstand adverse environments. Its cell wall is made up of proteins and has a pseudopeptidoglycan . Its flagella are long and thick and its structure can also be spherical, spiral, bacillary, laminar or lobed.

Nutrition of archaebacteria

Most of them can use inorganic compounds to be able to produce “food” or energy, which they use to keep their metabolic system working properly. It also has the ability to photosynthesize using sunlight to produce energy that is easy to use. Archaebacteria that inhabit the intestines of ruminants have a mutualistic function , which means that they feed on a part of the fiber that is consumed by these animals.


Archaebacteria have the ability to live in habitats under extreme conditions , in inhospitable areas that have high salinity , high temperature and in places where there are high concentrations of hydrogen , a situation that is not compatible with other types of life on the planet.


The main function of archaebacteria is to participate in the recycling of elements such as nitrogen , sulfur and carbon , which are found within ecosystems , eliminating the nitrogen present, assimilating nitrate and fixing nitrogen . They also have a relevant function in the oxidation of ammonia that is present in the soil, producing nitrites that will be oxidized by nitrates, a necessary product for plants and other types of organisms.


Some leading scientists believe that they may be responsible for some types of serious diseases for which the causes are unknown, such as arthritis, lupus, and Crohn’s disease. However, another part of the scientific community does not attribute any type of disease to him. What we do know with certainty is that they have the ability to dwell in animals and possibly in humans .

How they differ from eubacteria

Archaebacteria have a very simple organizational structure, they can be found in extreme environments , they have a round , plate , spiral , flat or a little square shape . Their cell wall is composed of peptidoglycans , they are not capable of producing the glycolysis process or the Krebs Cycle , they reproduce asexually by binary fission and the polymerase in their RNA consists of a complex pattern of subunits.

Eubacteria have a much more complex structure than archaebacteria and can also be located anywhere on earth . They have the shape of bacilli , vibrios , filaments or spirals and their cell wall is composed of peptidoglycans plus muramic acid . They have the capacity, contrary to archaebacteria, to be able to carry out the Krebs Cycle and of these there are only two types, the gram positive and the negative .


They have their main importance in the field of technology . Thanks to the extreme conditions in which they can develop, they are used to produce beneficial reactions in extreme conditions, such as in the treatment of wastewater while producing biogas . They are also stable with organic solvents, which is why they have started to be used in processes that are respectful with the environment .

Examples of archaebacteria

Some examples are:

  • Nanoarchaeum equitans
  • Halobacteria sp.
  • Sulfolobus sp.

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