All organisms are made up of cells which is the basic unit of life. Some are composed of single cells while others are composed of multiple cells. Archaea and Bacteria are two major single-celled or unicellular organisms categorised as Prokaryotes that is they do not have a well-defined nucleus and are lacking membrane-bound organelles. Even though both of them are Prokaryotes, they have a lot of differences.
Archaea vs Bacteria
The difference between Archaea and Bacteria is that the cell wall of Archaea does not have a polymer comprising of amino acids and sugars called peptidoglycan. The cell wall of Bacteria on the hand does have a mesh-like coating of peptidoglycan.
Archaea is a group of prokaryotes whose members that exhibit certain unique physical, physiological and genetic features distinguishing them from bacteria on one hand and eukaryotes on the other.
Bacteria, on the other hand, is a group of unicellular, microscopic organisms that can survive in virtually all environments including soil, water, organic matter and the bodies of multicellular organisms.
Also, the plasma membrane of Archaea has ether-linked (one atom of oxygen bonded with two aryl or alkyl groups) lipids. While the plasma membrane of Bacteria uses ester-linked (one oxygen atom bonded with two hydrocarbon groups) lipids.
Comparison Table Between Archaea and Bacteria (in Tabular Form)
|Parameter of Comparison||Archaea||Bacteria|
|Ribonucleic Acid (RNA)||Three||One|
|Reproduction||Budding, binary fission and fragmentation.||Produces spores so that it can survive for several years in a variety of conditions-favourable and unfavourable.|
|Found in||Unusual and extreme conditions like deeper regions of oceans, hot springs, swamps etc.||Almost everywhere like earth’s crust, organic matters, water bodies, bodies humans and animals and so on.|
|Cell Wall||Composed of S-layer or pseudopeptidoglycan.||Composed of peptidoglycan accompanied by muramic acid.|
|Major groups||Halophiles, Methanogens, Thermoacidophiles.||Gram-negative and Gram-positives.|
What is Archaea?
It is a group of single-celled microorganisms that do not have a well-defined nucleus and exhibit characteristics which distinguishes them from the other two branches of phylogenetic (evolutionary) tree.
When it was first discovered, it was put into the category of bacteria due to their resemblances in size and shape and was named as Archaebacteria. However, eventually it was discovered that Archaea exhibited certain features of Eukaryotes which were not present in bacteria. For example, Bacteria have only one RNA polymerases. While just like Eukaryotes, there are three RNA polymerases in Archaea.
Besides, it is believed that one of the ancestors of the present Archaea had given birth to Eukarya. Consequently, the category of Archaebacteria became obsolete.
The term Archaea is of Greek origin. It comes from the word archaios which means ‘primitive’, ‘archaic’ or ‘ancient’. The nomenclature is very much justified insofar as some Archaea members do show some primitive characteristics. For example, certain members of Archaea use inorganic compounds like sulphur or ammonia as their energy source. This characteristic feature of those Archaea members points to the fact that some of them were present on the earth when it was in a nascent stage.
The Archaea may be aquatic or terrestrial microorganisms. They show a diversity of shapes which includes spherical, rod-like, and spiral forms. Moreover, they can survive in various extreme conditions which even include very hot or salty environments.
Some of them survive on oxygen and produce methane as an end product whereas others do not. They reproduce asexually by a variety of mechanisms which binary fission, fragmentation and budding.
What is Bacteria?
It refers to a group of unicellular, microscopic and prokaryotic organisms that are found in virtually all environments like soil, water, organic matter and the bodies of multicellular organisms.
The four basic shapes of bacteria are bacillus (rod-like), vibrio (comma-shaped), coccus (spherical), and spirillum (spiral). Like Archaea, there is no well-defined nucleus in bacteria. The genetic material is not covered by a nuclear membrane. That is to say, it is naked.
Apart from the genomic DNA that is single chromosome or circular DNA, many bacteria contain another DNA that is small and circular and resides outside the genomic DNA. This smaller DNA are known as plasmids. They provide a distinct phenotypic (a combination of environmental and genetic effects) character to the bacteria. A major example of such character is resistance to antibiotics.
Based on the structure of their cell wall and their reaction to gram stain (staining with a violet dye to identify the species of bacteria), bacteria are classified into two main groups- gram-positive and gram-negative.
Gram-positive bacteria turn purple during the gram staining experiment and have a thick layer of peptidoglycan in their cell walls. Gram-negative bacteria, on the other hand, exhibit a pink colour when stained with the violet dye and possess a thin layer of peptidoglycan. Also, Gram-positive bacteria do not possess any outer lipid membrane while the contrary is the case for Gram-negative bacteria.
Although some bacteria can cause food poisoning and infectious diseases in human beings, most of them are harmless. Many bacteria are useful as well. For example, bifidobacteria reside in the digestive tract of the human body and enables the digestion of food.
Bacteria are also used in a variety of industrial processes, especially in the food industry. For example, the production of cheeses, yoghurt and pickles are not possible without bacterial reactions.
Main Differences Between Archaea and Bacteria
- Both Archaea and Bacteria are single-celled prokaryotes. But Archaea shows certain characteristics of Eukaryotes as well. Like Eukaryotes, they have three RNA. But bacteria contain only one Ribonucleic Acid (RNA).
- Archaea can exist in extreme and unusual conditions like salty water, hot springs, deeper regions of oceans, marshes and gastrointestinal tract of human beings. Bacteria, on the other hand, are almost omnipresent. They are found in water, soil, radioactive wastes and multicellular animals and so on.
- Both Archaea and Bacteria procreate asexually but their mechanisms are different. Archaea procreate by the mechanisms of budding, binary fission and fragmentation. Bacteria, on the other hand, procreate by producing spores so that they can remain latent for many years in all conditions.
- The cell wall of Archaea is not made up of peptidoglycan. It is made up of simpler connecting subunits called the S-layer or pseudopeptidoglycan. The cell wall of Bacteria, on the other hand, is composed of peptidoglycan accompanied by lipopolysaccharide.
- The plasma membrane of Archaea has lipids covered with hydrocarbons which are sometimes branched and form monolayers. These lipids have ether bonds that connect the glycerol backbones. While, the plasma membrane of Bacteria contains lipids having ester bonds and enclosed with fatty acids.
Archaea, Bacteria and Eukaryotes constitute three major domains of life. All living things are categorised into these domains based on their structural, genetic and biochemical features. Among these, Archaea and Bacteria are single-celled organisms. But they have considerable differences in terms of their genetic, physical and physiological features which is enough to categorise them into two separate domains of life.
However, it is interesting to note that this separation between Archaea and Bacteria is very recent. Earlier they constituted a single domain which was known as the Archaebacteria kingdom.