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Biological classification is the term that is used for grouping different living organisms into different groups according to their similarities and dissimilarities. Modern classification uses many new features to differentiate between species, but in ancient times it was based on similarities on the basis of their physical properties. This process of differentiating the species from each other and classifying them into different classes has not happened in one or two months, it had taken quite a few years for the researchers to collect the data and then to analyze it, and then classify them according to their properties. The beginning of the earth was 3.7 billion years ago. In all these years and now also every day new species are getting discovered. The diversity of animals is much more than we can ever think, all types of animals from the micro to macro level has discovered. There are many species in the existing time that have not been discovered yet. For this vast system to understand and memorized, it was a need of time to classify them. The father of biology i.e., Aristotle a Greek philosopher has begun the biological classification on the basis of mode of nutrition, habitat, etc. Then there is the modern 5-kingdom classification which includes Monera, Protista, Fungi, Plantae, and Animalia.


Monera is the first kingdom in the 5-kingdom classification system as it includes prokaryotic organisms, lacks a nucleus, and most are composed of single-celled organisms. In 1866, Ernst Haeckel was the one who proposed the taxon Monera. There are two divisions of Monera, i.e., Archaebacteria and eubacteria. This kingdom is believed not to include common recent ancestors. This kingdom includes all types of bacteria. The first ever bacteria were discovered by Antonie van Leeuwenhoek in 1675, and he named them ‘animalcules’ this bacterium was put under class Vermes in Animalia. The oldest known microorganisms which are known on the earth are put under this kingdom. These species lack nuclei and due to this their genetic material is also not enclosed, but it is loose inside the cell of these species. Monera is classified into three subkingdoms which are:

  • Archaebacteria
  • Eubacteria
  • Cyanobacteria

In this article, we are going to discuss Archaebacteria in detail, so let’s start.




Archaebacteria is a domain that consists of single-celled organisms. These are prokaryotes and don’t have a nucleus. Archaebacteria is the term that is usually used for these bacteria but later on, it is known as Archaea. The cells of the other two domains i.e., Eubacteria and Cyanobacteria don’t have some properties which are uniquely shown by Archaebacteria which makes it different from other subkingdoms. We can not isolate all the Archaebacteria in labs and so their classification is a bit tough because it is only done on the basis of the gene sequence that is taken from environmental samples. The size and the shape of Archaea and bacteria are similar but Archaea have different shapes in themselves like Haloquadratum walsbyi has flat square cells. The enzymes which are involved in translation and transcription are more related to eukaryotes, and some metabolic activities of Archaebacteria are similar to eukaryotes.


  • Archaebacteria can perform methanogens because they flourish where there is no oxygen, as they are facultative or obligate anaerobes.
  • Archaebacteria have cell membranes. The main component of cell membranes is lipids in Archaebacteria. Moreover, they have ether-linked phospholipids, while the rest (Bacteria and Eubacteria) have ester-linked phospholipids.
  • Sugar that is used in Archaebacteria is different from that which is used in bacteria’s cell membranes.
  • Most cells get burst out in hypotonic conditions, but this is not the case with Archaebacteria because they have rigid cell walls by which mechanical support is provided to the organism, which inhibits its bursting in extreme situations.
  • To protect Archaebacteria from the effects of the lysosome, its cell wall has Pseudomurein. Usually in a host body as an effect of the immune system lysosomes are produced which dissolved the cell wall of pathogenic bacteria, but this action gets restricted in Archaebacteria due to the presence of Pseudomurein in their cell wall.
  • The cytoplasm of these bacteria is thick and contains all nutritious components and also the components which are important for the metabolism of the species. They lack all the membrane-bound organelles like ER, Golgi apparatus, Lysosome, Nucleus, Mitochondria, etc.
  • The common name of Archaebacteria is extremophiles, as they can survive in extreme situations. For example, they can survive in extremely high temperatures and extremely acidic and alkaline conditions.
  • These bacteria have a specialty to survive under extremely high pressure, even more than 200 atmospheres.
  • Archaebacteria are resistant to antibiotics because they have antibiotic-resistance enzymes in their plasmids, so their nature toward antibiotics is a bit different.
  • These bacteria reproduce through binary fission which is an asexual mode of reproduction.
  • Transcription of genes is performed uniquely in this subkingdom.   
  • They diverge from both eukaryotes and prokaryotes, which is shown by the differences in their ribosomal RNA.

Classification of Archaebacteria

On the basis of phylogenetic relationships, Archaebacteria is divided into 5 divisions which are as follows-


The bacteria which can survive in a wide range of habitats is known as crenarchaeota. They can also survive in extremely high temperatures. To survive extremely high temperatures like 230 degrees Celsius, there is a need for many special proteins which are present in these bacteria. These bacteria also survive in highly acidic environments. The usual habitat of these bacteria is hot springs, deep-sea vents, and places where there is super-heated water All the hyperthermophiles, thermoacidophiles, and thermophiles are included in this category of Archaebacteria.


This category is specialized in surviving extreme alkaline conditions. The only bacteria to perform cellular respiration using carbon as an electron receptor is Euryarchaeota. There are only very few bacteria that can produce methane, and those bacteria fall under this category of Archaebacteria. Methanogens and halophiles are included under euryarchaeota.


The common factors of crenarchaeota, euryarchaeota, and korarchaeota are their genes. Common ancestors are present in all three categories. Hyperthermophiles are included under this subcategory as they have the ability to survive extra extremely high temperatures and these bacteria are believed to be the oldest existing bacteria on the earth.


The bacteria which have the ability to oxidize ammonia are kept under this category.


Ignicoccus is the genus to which these bacteria belong. These are the obligate symbiont of archaea.


  • A common definition of species is changed due to Archaebacteria because usually, species are those in which gene flows within its member, but it is not in Archaebacteria as here gene flows across its species.
  • Methanogens are included in Archaebacteria because they have the ability to produce methane. Methane which is used in cooking and lighting is produced when these bacteria act on organic matter and then organic matter decomposes to produce methane which further has many uses.



Loki’s castle is the location where this bacterium is found, which is located in deep-sea vents. These are thermophilic bacterium that has the ability to survive high temperatures. The genome of these bacteria is unique. The genes which are involved in phagocytosis are present in the genome of Lokiarchaeota. There are some genes in eukaryotic organisms which are used for maintaining the shape of the organism. Such genes are also found in this bacterium. The origin of eukaryotes and Lokiarchaeota are from the same ancestors, this was believed by some of the researchers due to the similarities found in Lokiarchaeota and eukaryotes. Lokiarchaeota is the transitional form between Archaea and Eukaryote.

Methanobrevibacter Smithii

As the name itself describe, it produces methane. The location of this bacterium is the human gut. The function which is assigned to this bacterium in the human gut is a breakdown of complex sugars. In consuming the energy from the food, we eat, this bacterium plays an important role. In a few cases, it is seen that it also provides protection against colon cancer. The level of Euryarchaeota bacteria is high in those individuals which are suffering from obesity and colon cancer.

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FAQs on Archaebacteria

Question 1: Give the characteristics of Archaebacteria.


  • Archaebacteria have some characteristic features, like they have ribosomal RNA’s and tRNAs.
  • The cell wall of Archaebacteria lacks peptidoglycan.
  • The bond in Archaebacteria is different as found in bacteria and eubacteria, i.e., they have ether-linked phospholipids.

Question 2: Explain the different habitats where Archaebacteria can be easily found.


There is a wide variety of habitats where Archaebacteria can be found as they have the ability to survive extreme conditions. They can be found in hot springs, in extreme acidic situations, in alkaline places, and many others.

Question 3: Is DNA present in Monera?


Yes, DNA is present in Monera but as the nucleus is not present so naked DNA is present which forms a clump and is called a nucleoid. This kingdom contains the species which is the oldest species present on the earth.

Question 4: What is the mode of nutrition of Monera?


The mode of nutrition in this kingdom is autotroph as all the bacteria are included in this category. These have their own chlorophyll and make their own food with the help of chlorophyll and sunlight.

Question 5: Explain the importance of biological classification.


The main importance of biological classification is for the correct identification of an organism. The origin and evolution of any particular species can be studied easily with the help of biological classification. The phylogenetic relations can determine between similar species with the help of such classification.

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Last Updated : 06 Dec, 2022
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