Archaea vs bacteria- Its differences with examples


Archaea and bacteria are two distinct categories in the vast field of microbiology that fascinate both academics and scientists. Despite their microscopic size, these microorganisms have a large impact on human health and have significant role in many ecosystems. The definitions of Archaea and Bacteria, their primary distinctions, and fascinating examples from each domain will all be covered in this article.

What is Archaea?

The single-celled microorganisms known as archaea, often known as “extremophiles,” have a unique cellular structure and genetic make-up. They may survive in a variety of Conditions, from hot springs and deep-sea hydrothermal vents with extremely high temperatures to extremely acidic or alkaline environments. Archaea are classified into Euryarchaeota, Crenarchaeota, and Thaumarchaeota, and each has its own special characteristics and adaptations.

What is Bacteria

Bacteria are single-celled microorganisms, like Archaea, but they have different genetic makeup and cell structures. Bacteria are everywhere on Earth and can be found in almost every environment, including soil, water, air, and even other living things. They come in a large variety of forms, sizes, and metabolic activities. Bacteria are classified into phylum which includes Proteobacteria, Firmicutes, and Actinobacteria, among others.

Archaea Vs Bacteria

DefinitionArchaea are a group of primitive prokaryotes that constitute a distinct domain separate from bacteria and eukaryotes, based on their unique characteristics.Bacteria are single-celled, primitive organisms that form a domain characterized by a wide range of shapes, sizes, structures, and habitats.
HabitatMost archaea are extremophiles and thrive in extreme environments such as the deep sea, mountains, hot springs, and salt brine.Bacteria inhabit diverse habitats, including soil, water, and both living and non-living organisms.
TypesArchaea are categorized into different groups, such as Methanogens, Thermophiles, and Halophiles, based on their distinctive characteristics.Bacteria are classified as Gram-negative or Gram-positive based on their response to Gram staining.
PhotosynthesisArchaea do not perform oxygen-generating photosynthesis but can be considered phototrophs, as they utilize sunlight as an energy source.Many bacteria possess photosynthetic pigments and are capable of performing photosynthesis to produce their own food.
Cell wallArchaea have cell walls composed of pseudopeptidoglycan, lacking D-amino acids and N-acetylmuramic acid.Bacterial cell walls are composed of peptidoglycan, which consists of N-acetylmuramic acid and D-amino acids.
Membrane lipidArchaeal membrane lipids contain fatty acids that are bound to glycerol by ether bonds.Bacterial membrane lipids contain fatty acids that are bound to glycerol by ester bonds.
Glucose oxidationArchaea have cell walls composed of pseudo peptidoglycan, lacking D-amino acids and N-acetylmuramic acid.Archaea do not rely on glycolysis or the Krebs cycle for glucose oxidation, but they follow metabolic pathways similar to these processes.
FlagellaArchaeal flagella, known as archaella, are formed by adding subunits at the base.Bacterial flagella are hollow structures that are assembled by adding subunits from the central pore towards the tip of the flagellum.
ReproductionArchaea reproduce through fission, budding, and fragmentation. They do not undergo sporulation.Certain bacteria can form spores that enable them to survive under extreme conditions for a specific period.
tRNAThymine is not present in the tRNA of archaea.Bacterial tRNA contains thymine.
tmRNAArchaea possess tmRNA (transfer messenger RNA).Bacteria contain tmRNA (transfer messenger RNA).
ChromosomesArchaeal chromosomes contain introns.Bacterial chromosomes do not contain introns.
RNA polymeraseArchaeal RNA polymerase is a complex enzyme composed of more than eight polypeptides and may include multiple RNA polymerases.Bacterial RNA polymerase is a simpler enzyme consisting of four polypeptides.
PathogenicityArchaea are generally non-pathogenic.Bacteria can be either pathogenic or non-pathogenic.
ExamplesExamples of archaea include Thermosphaera aggregans, Staphylothermus marinus, and Sulfolobus tokodaii.Bacteria utilize glycolysis and the Krebs cycle as crucial metabolic pathways for glucose oxidation.

Examples of Archaea


  • Methanogens are an intriguing species of archaea with the unusual capacity to create methane gas as a metabolic byproduct. 
  • They live in anaerobic habitats like marshes, swamps, and ruminant digestive systems. 
  • These microbes contribute significantly to the carbon cycle by turning organic matter into methane via a process known as methanogenesis.
  • Methanogens play an important role in biogas generation. Biogas is a sustainable energy source created by the anaerobic digestion of organic waste by associations of microorganisms that includes methanogens. 
  • Methanogens break down complex organic substances including agricultural waste, sewage sludge, and biomass to produce methane-rich biogas. 
  • This procedure not only provides a renewable energy source, but it also aids in trash management and minimizes greenhouse gas emissions.


  • Extremophiles are a varied group of microorganisms that grow in unfavorable environments. 
  • They have evolved amazing resistance to severe environments such as high temperatures, acidic or alkaline pH, high salinity, and high pressure. 
  • Thermophiles (adapted to high temperatures), acidophiles (suited to acidic conditions), and halophiles (adapted to high salt concentrations) are examples of extremophiles.
  • Archaea like Pyrococcus furiosus live at deep-sea hydrothermal vents, where temperatures can reach hundreds of degrees Celsius. 
  • These hyperthermophiles carry out their metabolic activities using specific heat-stable enzymes. Acidophilic archaea, such as Ferroplasma acidiphilum, may oxidize ferrous iron and contribute to the formation of acidic conditions in acidic environments, such as acid mine drainage sites.
  • Thermophiles: Thermophiles are archaea that thrive in high-temperature environments. They can be found in places like hot springs, hydrothermal vents, and geothermal areas. Thermus aquaticus is a well-known thermophilic bacterium that thrives in hot springs and is notable for its heat-resistant DNA polymerase, which is widely used in the polymerase chain reaction (PCR) technique.
  • Halophiles: Halophiles are archaea that thrive in high-salt environments. They can be found in salt flats, salt lakes, and salt pans. An example of a halophile is Halobacterium salinarum, which is known for its ability to survive in environments with extremely high salt concentrations. It has a reddish-pink color due to the presence of pigments such as bacteriorhodopsin.


  • Thaumarchaeota is a group of archaea that contribute significantly to the global nitrogen cycle. 
  • They are ammonia-oxidizing archaea (AOA), which convert ammonia to nitrite, which is an important stage in nitrification. 
  • Thaumarchaeota contributes to the availability of nitrate, which is required for the development of plants and other creatures. 
  • Their prevalence in a variety of environments emphasizes their ecological significance.
  • Thaumarchaeota has been discovered in a variety of marine settings, including coastal waters, open oceans, and deep-sea deposits. 
  • They are one of the most numerous groups of animals in the water, suggesting their importance in marine ecosystems. 
  • Thaumarchaeota are key contributors to total ecosystem productivity and nutrient dynamics due to their capacity to grow in low-nutrient settings and their role in nitrogen cycling.

Examples of Bacteria

E. coli 

  • Escherichia coli, sometimes known as E. coli, is a gram-negative bacteria found in the typical gut microbiota of humans and animals. While some strains of E. coli are harmful, others are not and have become useful model organisms for scientific research. 
  • The fast growth of E. coli, as well as its well-characterized genetics and simplicity of manipulation, have made it a powerful tool in molecular biology and biotechnology.
  • The traits and abilities of E. coli strains might vary. In research laboratories, 
  • for example, the strain E. coli K-12, notably the MG1655 strain, is often utilized. 
  • It has been thoroughly investigated, and its genome has been sequenced, allowing scientists to explore a variety of biological processes. 
  • Other strains, such as E. coli O157:H7, are known to be pathogenic and can cause serious foodborne infections.

Mycobacterium tuberculosis 

  • Mycobacterium tuberculosis is the bacterium that causes tuberculosis (TB), a worldwide infectious illness mostly affecting the lungs. 
  • TB is still a major public health issue, generating millions of infections and deaths each year. 
  • M. tuberculosis has a distinct cell wall structure and complicated biochemistry, which contribute to its capacity to escape the immune system and cause persistent infections.
  • M. tuberculosis is found all across the world, however, it is more prevalent in underdeveloped nations and populations with little access to healthcare. Tuberculosis control options include early detection, effective pharmacological therapy, and immunization. 

Staphylococcus aureus

  • S. aureus is a Gram-positive bacterium that is commonly found on the skin and mucous membranes of humans and animals. 
  • It can cause various infections, ranging from minor skin infections to more severe conditions such as pneumonia, bloodstream infections, and surgical site infections.

Bacillus subtilis

  • B. subtilis is a Gram-positive bacterium commonly found in soil, water, and the gastrointestinal tracts of humans and animals. 
  • It is known for its ability to form spores, which allow it to survive harsh environmental conditions. 
  • B. subtilis is widely used as a model organism in research and has industrial applications in enzyme production and bioremediation.


  • Tortora, G. J., Funke, B. R., & Case, C. L. (2021). Microbiology: An introduction. Pearson Education Limited.
  • Willey, J. M., Sandman, K. M., Wood, D. H., & Prescott, L. M. (2019). Prescott’s microbiology (11th ed.). McGraw Hill.
Mubashir Iqbal
Mubashir Iqbal

Mubashir Iqbal is a highly dedicated and motivated Microbiologist with an MPhil in Microbiology from the University of Veterinary and Animal Sciences. Currently, he is researching the efficacy of commercially available SARS Cov-2 vaccines to neutralize the omicron variant in Pakistan. He holds a Bachelor's degree in Microbiology and has experience in chemical and microbiological analysis of water samples, managing SOPs and documents according to standard ISO 17025. Additionally, he has worked as an internee in BSL 3, Institute of Microbiology, UVAS, where he gained experience in RNA extraction, sample processing, and microscopy.

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