Difference between archaea and bacteria

the archaea and the bacteria they are prokaryotes, unicellular living beings whose genetic material is not enclosed in an intracellular compartment.

Archaebacteria were initially considered bacteria, and in fact they were known as archaebacteria. Thanks to the studies of Carl R. Woese and technological advances in genetic sequencing, archaea and bacteria were separated into different phylogenetic groups. Living organisms are now classified into three domains:

  • Control bacteria: where the bacteria are.
  • Control Archaea: where archaebacteria are included.
  • Control Eukarya: where all eukaryotes (plants, fungi and animals) are included.
archaea bacteria
Control Archaea bacteria
Carbon bond of lipids ether Esther
Phosphate column of lipids Glycerol-1-phosphate Glycerol-3-phosphate
Metabolism Similar to bacteria bacterial
Location Extensive, they are located in extreme environments Wide
Transcription device Similar to eukaryotes bacterial
Nucleus and organelles Absent Absent
methanogenesis present Absent
pathogens No Yes
Ribosomal RNA subunit 16S 16S
Cellular wall Does not contain peptidoglycan Contains peptidoglycan
spores They do not form spores Some bacteria form spores
examples Halobacterium salinarum Escherichia coli


Halobacterium salinarum Fuentecaliente salt pans
Fuentecaliente salt pans in the Canary Islands, Spain. The yellow color is due to archaea Halobacterium salinarum.

Archaebacteria are microscopic organisms that were discovered just 130 years ago, although they were initially thought to be bacteria. Archaebacteria constitute the third branch of the tree of life, between bacteria and eukaryotes.

The first completely sequenced genome of an archaea was that of Methanococcus jannaschii published in 1996.

Characteristics of archaea

Archaebacteria have a structure similar to bacteria: circular DNA, plasma membrane, cell wall, cytoplasm and ribosomes. However, the cell membrane of archaea is characterized by the incorporation of isoprenoid lipids with ether bonds attached to a glycerol-1-phosphate base.

They have information processing systems like bacteria and eukaryotes, namely DNA replication, transcription and translation, although they are more similar to the latter.

They are microscopic in size, being as small as 400-500 nanometers. They present shapes similar to bacteria: rounded (cocci), cylindrical (bacilli) and irregular shapes. In fact, the first square microorganism (Haloquadratum walsbyi) was an archaea discovered in 1980 in the Sinai Peninsula.

the archaea they do not photosynthesize and neither do they form spores. They produce methane from biological compounds through the process of methanogenesis.

Archaea are beings that can live in extreme environments: or very high or very low temperatures. That is why they are classified as extremophiles. However, not all extremophile organisms are archaeogens, nor are all archaea extremophiles.

So far no pathogenic archaea are known, that is to say, that produce disease in animals or plants.

Control Archaea

The classification of archaea as a distinct domain arose from the studies of Carl Woese in the late 1960s using the sequence of ribosomal RNA as a marker. Thus, these organisms make up a separate domain of their own from bacteria and eukaryotes, domain Archaeawhich presents several main divisions or rows that grow as new specimens are studied.


Most are hyperthermophiles and thermoacidophiles. Thermoacidophiles (including hyperthermophiles, which grow fastest above 80ºC) colonize terrestrial volcanic environments and deep-sea hydrothermal vents. They can grow in the presence or absence of oxygen and be heterotrophic or autotrophic.

Examples of Crenarchaeota are Metallsphaera sedula (isolated from a volcano in Italy) i Thermoproteus neutrophilus (found in hot springs).


A large number of families with varied habitats are grouped in this section. For example, the methanogens they are found in anaerobic aquatic environments and in the gastrointestinal tract of animals, where they participate in the conversion of organic matter by using the metabolic products of bacteria (for example CO2hydrogen H2acetate and formate) and convert them into methane (CH4).

On the other hand, haloarchaea live in hypersaline environments (such as salt flats, lakes and the Dead Sea) where they grow as heterotrophs, often in association with phototropic algae. The square archaea Haloquadratum walsbyi is a halophilic representative.


It belongs to this group Nanoarchaeum equitans, the smallest archaea (400 nm) found so far. It was identified as small dots growing next to another archaea (Ignicoccus hospitalis).


This division was recognized in 2008 and its members are widely distributed in marine environments of medium temperatures. An example is the Nitrosopumilus maritimusfound in a tropical marine tank at the Seattle Aquarium, in Washington (USA).


Bacteria Aeromonas hydrophila
Some bacteria can be grown in special media (Image of colonies of aeromones hydrophila on agar, taken by Nathan Reading)

Bacteria are prokaryotic unicellular microorganisms, that is to say they do not have a nucleus defined by a nuclear membrane. They are widely distributed in the biosphere and were the first ancestral life forms.

There are more bacterial cells than human cells in the human body. The bacteria that reside in the gut are called gastrointestinal microbiome and they play a fundamental role in the state of health of the individual.

Of the wide variety of known bacterial species, only a few are pathogenic to humans, the vast majority are harmless. Examples of pathogenic species are the Haemophilus influenzae (which can cause meningitis and pneumonia in children under five) and the Vibrio cholerae (which causes cholera).

Characteristics of bacteria

Bacterial cells possess circular chromosomal DNA, plasmids, cell membrane, cytoplasm, ribosomes and cell wall.

The bacterial cell wall it contains peptidoglycans composed of polysaccharide chains that are interconnected with unusual peptides. It works as a protective layer and gives shape to the bacterium. The forms of bacteria are varied; they can be spherical, cylindrical, spiral or comma-shaped.

Some bacteria have a capsule outside the cell wall. The capsule allow bacteria to adhere to surfaces, protect against dehydration and attack by phagocytic cells.

The plasmids they are small fragments of DNA that are separated from the main DNA (chromosomal DNA) and that can be transmitted between bacteria.

Some species have flagella that are used for locomotion and pili that are used to adhere to surfaces.

Control bacteria

Bacteria are divided into two large groups according to their reaction to a staining technique: Gram-positive and Gram-negative. This staining was invented by Hans Christian Gram (1853-1938).

the Gram-positive bacteria they have a cell wall composed of up to 90% peptidoglycans and the rest by teichoic acids. Examples of Gram-positive bacteria are staphylococci Staphylococcus aureus which is found in the skin.

the Gram-negative bacteria they have a relatively thin cell wall with only 10% peptidoglycans, covered by an external envelope composed of lipopolysaccharides and lipoproteins. Examples of Gram-negative bacteria are meningococci Neisseria meningitidiscausative agent of meningococcal meningitis.

The domain Bacteria (formerly called Eubacterium) represents the first branch of the tree of life division. This group presents a great variety of row of which we can mention:

  • Proteobacteria: Gram-negative organisms such as Escherichia coli and the Salmonella sp.
  • Chlamydia: Gram-negative aerobic pathogenic organisms such as Chlamydia trachomatis i Chlamydia pneumoniae.
  • Spirochetes: bacteria with wavy shapes like the Spirochaeta halophila.
  • Cyanobacterium: bacteria that carry out photosynthesis.
  • Gram-positive bacteria: such as lactobacilli, which produce lactic acid and are used in making yogurt.

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Differences between archaea and bacteria

The main differences between archaea and bacteria are in the composition of the membrane and cell wall, metabolism and genetic machinery.

Composition of the plasma membrane

phospholipids archa and bacteria
Differences in cell membrane and phospholipids between archaea and bacteria.

The cell membrane of archaea differs from bacteria in types of phospholipids that make it up Bacteria’s membrane phospholipids are made up of two linear chains of fatty acids, linked by ester bonds to a glycerol with a phosphate group at the third carbon. Two layers of these phospholipids form the membrane. This is why it is called a lipid bilayer and is similar to the membrane structure of eukaryotes.

On the other hand, the phospholipids in the archaea membrane are made up of long (20 to 25 carbons) and branched chains of isoprenoids, which are joined at each end by ether bonds to a glycerol, which in this case has a phosphate group at the first carbon. This type of phospholipid forms a lipid monolayer.

Cellular wall

Unlike bacteria, the cell wall of archaebacteria does not contain peptidoglycan and is composed of proteins, polysaccharides or glycoproteins. Some archaea have a pseudopeptidoglycan with different sugars in the polysaccharide.


A characteristic that distinguishes certain species of archaea from bacteria is their ability to generate methane from carbon dioxide and other organic compounds such as acetate and formate. Although archaebacteria can generate their energy source from light, they do not carry out the process of photosynthesis, as cyanobacteria do.

Genetic machinery

Genetic information processing in archaea is more similar to eukaryotes than to bacteria. While bacterial DNA has one origin of replication, archaeal DNA has multiple replication initiation sites. The first amino acid in protein synthesis in bacteria is formyl-methionine, while in archaea it is methionine.

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