Bacteria and archaea

Archaea and bacteria are two types of microorganisms that belong to the category of prokaryotes. However, not all of them are prokaryotic. Previously, archaea were classified as bacteria, but no longer, because both have been found to have different biochemistry and different evolutionary history. Read on to find the differences between them!



DefinitionArchaea are a group of primitive prokaryotes that, based on their distinctive characteristics, form a separate domain from bacteria and eukaryotes.Bacteria are primitive single-celled 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 such as deep sea, mountains, hot springs, brine, etc.Bacteria reside in different habitats ranging from soil, water, to the interior of living and non-living organisms.
Cellular wallThe archaic cell wall is made up of pseudopeptidoglycan and lacks D-amino acids and N-acetylmuramic acid.The bacterial cell wall is made up of peptidoglycan consisting of N-acetylmuramic acid and D-amino acids.
Membrane lipidFatty acids in archaea membrane lipids are linked to glycerol by ether bonds.Fatty acids in bacterial membrane lipids bind to glycerol through ester bonds.
Glucose oxidationArchaea do not use glycolysis or the Kreb cycle for glucose oxidation, but rather follow similar metabolic pathways.Glycolysis and the Kreb cycle are important metabolic pathways in bacteria for the oxidation of glucose.
PhotosynthesisArchaea do not carry out oxygen-generating photosynthesis, but they are phototrophs, using sunlight as an energy source.Many bacteria that contain photosynthetic pigments can photosynthesize to prepare their own food.
TypesArchaea are divided into different groups such as methanogens, thermophiles, and halophiles based on their characteristics.Bacteria are divided into Gram negative and Gram positive based on their response to Gram stain.
FlagellaArchaeological flagella are synthesized by adding subunits at the base.Bacterial flagella are hollow and assembled by adding subunits that move from the central pore to the tip of the flagella.
ReproductionArchaea reproduce by fission, budding, and fragmentation. Sporulation does not occur in archaea.Some bacteria are capable of forming spores that help them survive in extreme conditions for a certain period of time.
ARNtThymine is absent from archaea t-RNA.Thymine is present in the t-RNA of bacteria.
tmRNAThe mRNA (transfer messenger RNA) is found in archaea.TmRNA is found in bacteria.
ChromosomesIntrons are present on the chromosomes of archaea.Introns are absent from the chromosomes of bacteria.
Polymers of ARNRNA polymerase in archaea is complex with more than eight polypeptides. They could even have multiple RNA polymerases.Bacterial RNA polymerase is simple, with four polypeptides.
PathogenicityArchaea are not pathogenic.Bacteria can be pathogenic or non-pathogenic.
ExamplesThermosphaera aggregans, Staphylothermus marinus, Sulfolobus tokodaii.Pseudomonas aeruginosa, Bacillus subtilis, Staphylococcus aureus, Salmonella typhi.

Definition of archaea

Archaea are a group of primitive prokaryotes that, based on their distinctive 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.

They generally inhabit extreme environments such as deep-sea vents, saline waters, hot springs, and even under oil reservoirs. They are mostly anaerobic, live in low oxygen environments and cannot be grown in laboratories, therefore they must be identified using culture independent techniques.

Organisms in this domain can share some characteristics with both bacteria and eukaryotes. They have a nascent membraneless nucleus like bacteria, but they share some genes, metabolic pathways, and enzymes that are also seen in eukaryotes. However, these organisms also have some unique characteristics. Archaea membrane lipids contain fatty acids bound to the glycerol molecule by ether bond rather than 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 and facilitate 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 help process the biogeochemical cycles of various elements such as carbon, nitrogen, and sulfur.

Many archaea are methanogens that use anaerobic cellular respiration to produce methane as a by-product. Although oxygen-generating photosynthesis does not occur in these organisms, some of them (phototrophs) use sunlight as a source of energy.

Definition of bacteria

Bacteria are primitive single-celled organisms that form a domain of organisms diverse in shape, size, structure, and even habitats. They are prokaryotes that have a membraneless nucleus and lack many cellular organelles, making them simple in structure and function.

It includes organisms found in many different life forms, from high mountains to the interior of the body of other organisms. Some bacteria are beneficial and help in various purposes, such as antibiotic production, industrial use, and biogeochemical cycling. However, some are pathogenic organisms that cause mild to severe disease.

Bacteria are the smallest living entities in the world and they are microscopic. These organisms are observed under the microscope by performing a series of staining techniques. According to 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 bacteria from harmful chemicals. The cytoplasm has few ribosomes and an incipient, membraneless nucleus that contains the genetic material. The membrane lipids in bacteria are composed of fatty acids linked to glycerol by ester bonds.

Bacteria also have a unique RNA called transfer messenger RNA (tmRNA). The genetic material of bacteria is the DNA that is transferred to their descendants through asexual reproduction . The latter takes place through binary fission, budding and fragmentation, but there are different methods such as transformation, transduction and conjugation for the transfer of genetic materials.

Examples of archaea


  • Sulfolobus is a genus of organisms that belong to the 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 mainly found in volcanic springs.
  • The proteins found in Sulfolobus are particularly important in biotechnology as they are thermostable and can also function at low pH.
  • These microorganisms are also special because they use sulfur as the final electron acceptor during cellular respiration.
  • Therefore, these depend on sulfur for the autotrophic or heterotrophic mode of nutrition.
  • Sulfolobus was also used as a model for the study of DNA replication. Multiple replication origin sites were identified during studies of these organisms.
  • Some species belonging to this genus are Sulfolobus tokodaii and Sulfolobus metallicus.


  • Methanogens are prokaryotes belonging to archaea that are so named because they produce methane as a by-product during metabolic activities.
  • These are mainly found in wetlands and within the gastrointestinal tract of various ruminants and even humans.
  • Some methanogens are extremophiles and are found in hot springs and deep-sea vents.
  • More than 50 species of methanogens are known, 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 through anaerobic respiration.
  • Methanogens are mainly used in wastewater treatment through biological 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 small intestines of humans and other warm-blooded animals.
  • Most varieties of E. coli are harmless, but few can cause mild to severe diarrhea. Some microbes even produce vitamin K and vitamin B-12.
  • E. coli is a gram-negative and facultative anaerobic that blooms at room temperature.
  • They are rod-shaped and have short life cycles, making them ideal for research studies.
  • E. coli does not produce spores and has peritrichous flagella.


  • Lactobacillus is a group of gram-positive microorganisms
  • The term Lactobacilli is used to indicate its ability to produce lactose as a by-product of glucose metabolism.
  • These organisms are mainly found in milk and dairy products.
  • Many varieties of lactobacillus are used commercially to produce fermented milk products and different vegetables.
  • Some species of this genus in common use are Lactobacillus brevis, Lactobacillus casei and Lactobacillus plantarum.
  • These organisms are even found within the body of living beings such as the intestine and vagina of human beings.

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