Difference between Archaea and Bacteria

Archaea and bacteria have evolved 3.5 billion years ago. Both are representatives of prokaryotic cells and include in the Monera Kingdom. Although both archaea and bacteria belong to the prokaryotic category, they show profound variations in genetic makeup. Metabolic pathways, genes, and enzymes of the Archaea resemble the eukaryotic cells.

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Bacteria are the first to form of life on the earth with small sizes and various shapes. They are found ubiquitously everywhere and sometimes cause harm to humans and sometimes provide certain benefits to humans.

Archaea are the most primitive form of the living microorganism on the earth and named archaebacteria previously but now termed as archaea because of showing specific characteristics of eukaryotic cells.

Comparison Chart

Basis for Comparison Archaea Bacteria
Definition Archaea are most primitive single-celled microorganism and live in extreme temperatures Bacteria are single-celled microorganisms with complex structures.
Another name Archaebacteria Eubacteria
Shape Cocci, Rods, spiral, plates or coils Cocci, Rods, spiral, plates or coils
Habitat Extreme temperatures such as springs, salt lakes, marshlands, oceans, the gut of ruminants and humans Found everywhere, soil, hot springs, earth’s crust, plant and animal bodies, organic matter and radioactive waste, etc
Lipid membrane Pseudopeptidoglycan Lipopolysaccharides, muramic acid and peptidoglycan
RNA Consists of three RNA Consists of single RNA
Metabolic Pathways Methanogenesis Aerobic anaerobic respiration, autotrophy, fermentation, and photosynthesis.
Reproduction Asexual reproduction by budding, binary fission and fragmentation. Asexual reproduction
Types Methanogens, Halophiles, Thermoacidophiles Gram-positive and gram-negative bacteria
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What is Archaea?

Archaea have special characteristics of surviving under extreme temperatures so they are known as extremophiles. These are single-celled microorganisms as other bacteria with an undeveloped nucleus and no organelle. Their genetic material is in the form of a loop which is called plasmid. Anatomy and physiology of archaea are similar to eukaryotic organisms which are the distinctive feature of this group. Archaea size ranges from 0.5 to 4 micrometers and has rods, spirals, plates, and spheres. Archaea are different from other bacteria because of cell membrane which is composed of pseudo peptidoglycans which are composed of peptidoglycan in case of other bacteria. In pseudo peptidoglycans, lipid membranes are ether-linked with additional branching of aliphatic acids. This membrane acts as a barrier in the cell and outer environment. It is surrounded by a cell wall and helps to maintains its shape and chemical equilibrium.

Archaea possess a single circular chromosome in plasmid form which divides asexually by budding, binary fission and fragmentation. Archaea have one flagellum which helps in the locomotion and to identify unfavorable conditions for survival. They are mostly metabolically active in the situation of acids, pH, pressure, high temperature, and deep water.

Archaea are of three type; methanogens, thermophiles, and halophiles. Methanogens are a very diverse group of archaea and play an important role in wastewater treatment. These can convert bacterial waste products and carbon dioxide into methane. Methane is considered a greenhouse gas and help in reducing global warming. Methanobacterium is an example of this group. Thermophiles are the types of archaea that can survive at higher temperatures 106° to 252° F. They can be divided into further into three classes; simple thermophile, extreme thermophile or hyperthermophiles. This group has a salient role in biotechnology while performing a Polymerase Chain Reaction. Its common examples are Thermus aquaticus and Thermuococcus litoralis. Halophiles, the third type, are known as salt-loving extremophiles. These are fond of living in high salt concentration like in evaporation ponds, the deep sea of the Dead Sea and the Great Salt Lake. Halococcus and Halobacterium are examples of halophile estraea.

What are the Bacteria?

Bacteria, also known as Eubacteria are the prokaryotic microorganism which lacks the nucleus and membranous bound organelles. All the processes take place in the cytoplasm. The bacterial cell is surrounded by a membrane that supports, protects and regulates the transport of materials. Bacteria have a single chromosome as genetic material and ribosomes for the synthesis of proteins. The cell wall of the bacteria is composed of peptidoglycan which has ester linkage of fatty acids. They also possess some special appendages for mobility and have the ability to reproduce even in high temperatures. Bacteria can reproduce sexually as well as asexually.

For humans, bacteria can be harmful as well as beneficial. Some bacteria cause infections and different other diseases in humans such as pneumonia etc. But some bacteria are very helpful for humans such as help in curdling milk into yogurt and indigestion.

Because of the cell wall composition and color on staining, bacteria can be divided into two types; gram-positive and gram-negative bacteria. Gram-positive bacteria have a cell wall composed of peptidoglycan and murein whereas the cell wall of gram-negative bacteria has a thin layer of peptidoglycan and lipopolysaccharides.  Gram-positive bacteria give positive results and appear purple under a microscope whereas gram-negative bacteria appear as crystal violet in color. Staphylococcus, Bacillus, and streptococcus are examples of gram-positive bacteria whereas Salmonella, Shigella, and Pseudomonas are examples of gram-negative bacteria.

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Key Differences between Archaea and Bacteria

  1. Archaeal cell wall does not contain peptidoglycan whereas bacterial cell wall contains peptidoglycan (molecules made up of both sugar and protein ring).
  2. Archaea have three ribosomal RNA polymerase whereas bacteria have one ribosomal RNA polymerase.
  3. In archaea, thymine is absent in tRNA and introns are present whereas in bacteria thymine is absent in tRNA and introns are present.
  4. Archaea are extremophiles and can survive in very high temperatures whereas bacteria cannot live on 100 degrees Celsius temperature.
  5. Archaeal growth cannot be inhibited by antibiotics whereas bacterial growth can be inhibited by the use of antibiotics in case of illness.

Key Similarities

  1. Both fall in the category of prokaryotes.
  2. Both have a very small size which varies from 0.5 to 4 microns.
  3. Both lack nucleus and membrane-bound organelles.
  4. Both are types of autotrophs and heterotrophs.
  5. Both possess 70 S ribosomes.


In sum, archaea and bacteria both belong to prokaryotes but archaea have some characteristics common with eukaryotic cells and bacteria are more complex microorganisms.

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