Archaea vs Bacteria- Definition, 15 Major Differences, Examples

Differences between Archaea and Bacteria (Archaea vs Bacteria)

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Archaea Definition

Archaea is a group of primitive prokaryotes that based on their distinct characteristics form a separate domain from bacteria and eukaryotes.

  • The term ‘Archaea’ is derived from a Greek word, ‘archaios’ which means primitive or ancient, indicating the primitive structure of these organisms.
  • These organisms usually inhabit extreme environments like deep-sea vents, saline waters, hot springs, and even below petroleum deposits.
  • These are mostly anaerobic and live in low-oxygen environments. Most of the archaea cannot be cultured in laboratories and thus, have to be identified through culture-independent techniques.
  • Organisms in this domain might share some characteristics with both bacteria and eukaryotes. They have an incipient membrane-less nucleus like bacteria but share some genes, metabolic pathways, and enzymes that are also observed in eukaryotes.
  • However, these organisms also have some unique characteristics. The membrane lipids of archaea contain fatty acid linked to glycerol molecule by ether bond instead of ester bond as in bacteria and eukaryotes.
  • Because archaea inhabit many extreme environments, they tend to have distinct metabolic pathways as well as genes that support their survival. Halophilic archaea have a unique set of genes that limit the extent of osmosis, facilitating their survival.
  • Reproduction in archaea is asexual by budding, fission, and fragmentation. The usual division process of mitosis and meiosis does not take place.
  • Most archaea aid the process of biogeochemical cycles for various elements like carbon, nitrogen, and sulfur.
  • Many archaea are methanogens that utilize anaerobic cellular respiration to produce methane as a by-product.
  • Even though oxygen-generating photosynthesis doesn’t occur in these organisms, some of them (phototrophs) use sunlight as a source of energy.

Bacteria Definition

Bacteria are single-celled primitive organisms that form a domain of organisms diverse in shape, size, structure, and even habitats.

  • Bacteria are prokaryotes that have a membrane-less nucleus and lack many cell organelles, which make them simple in structure and function.
  • The domain Bacteria includes organisms that are found in many different forms of life from high mountains to inside the body of other organisms.
  • Some bacteria are beneficial that help in various purposes like antibiotics production, industrial use, and biogeochemical cycles. However, some are pathogenic organisms that result in mild to severe diseases.
  • Bacteria are the smallest living entities in the world and are microscopic. These organisms are observed under a microscope by performing a number of staining techniques.
  • Based on the staining techniques, bacteria are divided into Gram-positive and Gram-negative bacteria.
  • Almost all bacteria have a cell wall made up of peptidoglycan that protects the bacteria against harmful chemicals. The cytoplasm has few ribosomes and a membrane-less incipient nucleus containing the genetic material.
  • The membrane lipids in bacteria are composed of fatty acids bound to glycerol by ester bonds.
  • Bacteria also have a unique RNA called transfer-messenger RNA (tmRNA).
  • The genetic material in bacteria is DNA which is transferred to their offsprings via asexual reproduction.
  • Reproduction takes place through binary fission, budding, and fragmentation but different methods like transformation, transduction, and conjugation are available for the transfer of genetic materials.

Key Differences (Archaea vs Bacteria)

Basis for ComparisonArchaeaBacteria
DefinitionArchaea is a group of primitive prokaryotes that based on their distinct characteristics form a separate domain from bacteria and eukaryotes.Bacteria are single-celled primitive organisms that form a domain of organisms diverse in shape, size, structure, and even habitats.
HabitatMost archaea are extremophiles and are found in extreme environments like the deep sea, mountains, hot springs, salt brine, etc.Bacteria reside in different habitats ranging from soil, water to inside living, and non-living organisms.
Cell wallThe archaeal cell wall is made up of pseudopeptidoglycan and lack D-aminoacids and N-acetylmuramic acid.The bacterial cell wall is made up of peptidoglycan consisting of N-acetylmuramic acid and D-amino acids.
Membrane lipidThe fatty acids in membrane lipids of archaea are bound to glycerol by ether bonds.The fatty acids in membrane lipids of bacteria are bound to glycerol by ester bonds.
Glucose oxidationArchaea do not use glycolysis or Kreb’s cycle for glucose oxidation but follow metabolic pathways similar to these.Glycolysis and Kreb’s cycle are important metabolic pathways in bacteria for glucose oxidation.
PhotosynthesisArchaea do not perform oxygen-generating photosynthesis but are phototrophs, that use sunlight as a source of energy.Many bacteria containing photosynthetic pigments can perform photosynthesis to prepare their own food.
TypesArchaea are divided into different groups like Methanogens, Thermophiles, and Halophiles on the basis of their characteristics.Bacteria are divided as Gram-negative and Gram-positive based on their response to Gram staining.
FlagellaArchaeal flagella, also termed archaella, are synthesized by adding subunits at the base.Bacterial flagella are hollow and are assembled by adding subunits moving from the central pore towards the tip of the flagella.
ReproductionArchaea reproduce by fission, budding, and fragmentation. Sporulation doesn’t occur in archaea.Some bacteria are capable of forming spores that help them survive extreme conditions for a particular period of time.
tRNAThymine is absent in the t-RNA of archaea.Thymine is present in the t-RNA of bacteria.
tmRNAtmRNA (transfer messenger RNA) is found in archaea.tmRNA is found in bacteria.
ChromosomesIntrons are present in the chromosomes of archaea.Introns are absent in the chromosomes of bacteria.
RNA polymeraseRNA polymerase in archaea is complex with more than eight polypeptides. They might even have multiple RNA polymerases.Bacterial RNA polymerase is simple, with four polypeptides.
PathogenicityArchaea are non-pathogenic.Bacteria might be pathogenic or non-pathogenic.
ExamplesThermosphaera aggregans, Staphylothermus marinus, Sulfolobus tokodaii.Pseudomonas aeruginosa, Bacillus subtilis, Staphylococcus aureus, Salmonella Typhi.

Examples of Archaea


  • Sulfolobus is a genus of organisms that belong in the domain Archaea and are both acidophilic and thermophilic in nature.
  • They grow at a pH of 2-3 and a temperature of about 80°C. These are mostly found in volcanic springs.
  • The proteins found in Sulfolobus are particularly important in biotechnology as they are thermostable and also can function at low pH.
  • These microorganisms are also special because they utilize sulfur as the final electron acceptor during cellular respiration.
  • These are thus, dependent on sulfur for the autotrophic or heterotrophic mode of nutrition.
  • Sulfolobus was also used as a model for the study of DNA replication. Multiple sites of origin of replication were identified during studies on these organisms.
  • Some species belonging to this genus are Sulfolobus tokodaii and Sulfolobus metallicus.


  • Methanogens are prokaryotes belonging to the domain Archaea which are named so because they produce methane as a by-product during metabolic activities.
  • These are found mostly in wetlands and inside the gastrointestinal tracts of various ruminants and even human beings. Some methanogens are extremophiles and are found in hot springs and deep-sea vents.
  • There are more than 50 species of methanogens known so far, many of which produce methane through different metabolic pathways.
  • Some methanogens reduce carbon dioxide in the presence of hydrogen to produce methane. However, others produce methanol via anaerobic respiration.
  • Methanogens are mostly used in the treatment of wastewater via bio composition, which is a cost-effective and faster wastewater treatment process.
  • Some common species of methanogens are Methanosarcina bakeri, Methanosarcina acetivorans, and Methanococcus maripaludis.

Examples of Bacteria

Escherichia coli (E. coli)

  • E. coli is a model microorganism used for various research studies. These organisms are found in multiple environments, and many are found in the lower intestine of human beings and other warm-blooded animals.
  • Most varieties of E. coli are harmless, but few might cause mild to severe diarrhea. Some microbes even produce Vitamin K and Vitamin B-12.
  • E. coli is a Gram-negative and facultative anaerobe that flourishes at room temperature.
  • It is rod-shaped and has short lifecycles which makes it ideal for research studies.
  • E. coli are non-sporing and have peritrichous flagella.


  • Lactobacillus is a group of rod-shaped, Gram-positive, non-spore-forming microorganisms belonging to the family
  • The term Lactobacilli is given to indicate their ability to produce lactose as a by-product of glucose metabolism.
  • These organisms are mostly found in milk and milk products.
  • Many varieties of lactobacillus are used commercially to produce fermented products of milk and different vegetables.
  • Some commonly used species of this genus are Lactobacillus brevis, Lactobacillus casei, and Lactobacillus plantarum.
  • These organisms are even found within the body of living beings like in the intestine and vagina of human beings.

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About Author

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Anupama Sapkota

Anupama Sapkota has a bachelor’s degree (B.Sc.) in Microbiology from St. Xavier's College, Kathmandu, Nepal. She is particularly interested in studies regarding antibiotic resistance with a focus on drug discovery.

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