por The main differences between archaea and bacteria They are based on molecular-structural and metabolic aspects that we will develop below. The Archaea domain taxonomically groups unicellular microorganisms that have prokaryotic cell morphology (without a nuclear membrane or cytoplasmic organelle membranes), characteristics that resemble bacteria.
However, there are also features that separate them, since archaea are endowed with very particular adaptation mechanisms that allow them to live in environments of extreme conditions.
The bacteria domain contains the most abundant forms of bacteria called eubacteria, or true bacteria. These are also unicellular, microscopic, prokaryotic organisms that live in any environment of moderate conditions.
Differential Characteristics of Archaea and Bacteria
The organisms of Archaea and Bacteria have common characteristics in that both are free or aggregated unicellular. They do not have a defined nucleus or organelles, they have a cell size between 1 and 30μm on average.
They present significant differences with respect to the molecular composition of some structures and the biochemistry of their metabolisms.
Habitat
Bacteria species live in a wide range of habitats: they have colonized brackish and fresh waters, hot and cold environments, marshes, marine sediments and rock fissures, and can also live in atmospheric air..
They can coexist with other organisms within the digestive tracts of insects, mollusks and mammals, oral cavities, respiratory and urogenital tracts of mammals, and blood of vertebrates.
Also the microorganisms belonging to Bacteria can be parasites, symbionts or commensals of fish, roots and stems of plants, of mammals; they can be associated with lichen fungi and with protozoa. They can also be food contaminants (meat, eggs, milk, shellfish, among others).
The species of the Archaea group have adaptation mechanisms that make it possible to live in environments with extreme conditions; They can live at temperatures below 0 °C and above 100 °C (a temperature that bacteria cannot support), in extreme alkaline or acid pH and saline concentrations much higher than those of seawater.
Methanogenic organisms (producing methane, CH4) also belong to the Archaea domain.
plasma membrane
The envelope of prokaryotic cells, in general, is formed by the cytoplasmic membrane, the cell wall and the capsule.
The plasmatic membrane of the organisms of the Bacteria group does not contain cholesterol or other steroids, but rather linear fatty acids attached to glycerol by ester-type unions.
The membrane of members of Archaea can be made up of a lipid monolayer or bilayer, which never contain cholesterol. Membrane phospholipids are made up of long-chain, branched hydrocarbons linked to glycerol by ether-type bonds.
Cellular wall
In organisms of the Bacteria group, the cell wall is made up of peptidoglycans or murein. Archaeal organisms possess cell walls that contain pseudopeptidoglucan, glycoproteins, or proteins, as adaptations to extreme environmental conditions.
Additionally, they can present an external layer of proteins and glycoproteins, covering the wall.
ribosomal ribonucleic acid (rRNA)
The rRNA is a nucleic acid that participates in protein synthesis –production of the proteins that the cell requires to fulfill its functions and for its development-, directing the intermediate steps of this process.
The nucleotide sequences in ribosomal ribonucleic acids are different in Archaea and Bacteria organisms. This fact was discovered by Carl Woese in his 1990 studies, which led to the separation into two different groups to these organisms.
endospore production
Some members of the Bacteria group can produce survival structures called endospores. When environmental conditions are very adverse, endospores can maintain their viability for years, with practically zero metabolism.
These spores are extraordinarily resistant to heat, acids, radiation and various chemical agents. In the Archaea group, no species that form endospores have been reported..
Motion
Some bacteria have flagella that provide them with mobility; Spirochetes have an axial filament by means of which they can move in liquid, viscous media such as sludge and humus.
Some purple and green bacteria, cyanobacteria, and Archaea possess gas vesicles that allow them to move by buoyancy. Known Archaea species do not have appendages such as flagella or filaments.
Photosynthesis
Within the Bacteria domain, there are species of cyanobacteria that can carry out oxygenic photosynthesis (which produces oxygen), since they have chlorophyll and phycobilins as accessory pigments, compounds that capture sunlight.
This group also contains organisms that perform anoxygenic photosynthesis (which does not produce oxygen) through bacteriochlorophylls that absorb sunlight, such as: red or purple sulfur and red non-sulfur bacteria, green sulfur bacteria, and green non-sulfur bacteria.
In the Archaea domain, no photosynthetic species have been reported, but the genus Halobacterium, from extreme halophytes, is capable of producing adenosine triphosphate (ATP), using sunlight without chlorophyll. They have the retinal purple pigment, which binds to membrane proteins and forms a complex called bacteriorhodopsin.
The bacteriorhodopsin complex absorbs energy from sunlight and when it is released it can pump H+ ions out of the cell and promote the phosphorylation of ADP (adenosine diphosphate) to ATP (adenosine triphosphate), from which the microorganism obtains energy.
References
Barraclough TG and Nee, S. (2001). Phylogenetics and speciation. Trends in Ecology and Evolution. 16:391-399.
Doolittle, W.F. (1999). Phylogenetic classification and the universal tree. Science. 284:2124-2128.