Prokaryote

A prokaryote (/proʊˈkærioʊt, -ət/; less commonly spelled procaryote)[1] is a single-celled organism whose cell lacks a nucleus and other membrane-bound organelles.

[3] In the earlier two-empire system arising from the work of Édouard Chatton, prokaryotes were classified within the empire Prokaryota.

[8][9] Bacterial cells have various shapes, including spherical or ovoid cocci, e.g., Streptococcus; cylindrical bacilli, e.g., Lactobacillus; spiral bacteria, e.g., Helicobacter; or comma-shaped, e.g., Vibrio.

Bacterial biofilms are often made up of microcolonies (dome-shaped masses of bacteria and matrix) separated by channels through which water may flow easily.

This structure functions as a simple circulatory system by moving water through the biofilm, helping to provide cells with oxygen which is often in short supply.

[30][31] Bacterial biofilms may be 100 times more resistant to antibiotics than free-living unicells, making them difficult to remove from surfaces they have colonized.

Soil prokaryotes are still heavily undercharacterized despite their easy proximity to humans and their tremendous economic importance to agriculture.

[40][41][42] Another view is that the three domains of life arose simultaneously, from a set of varied cells that formed a single gene pool.

[45] According to the 2016 phylogenetic analysis of Laura Hug and colleagues, using genomic data on over 1,000 organisms, the relationships among prokaryotes are as shown in the tree diagram.

[46] The distinction between prokaryotes and eukaryotes was established by the microbiologists Roger Stanier and C. B. van Niel in their 1962 paper The concept of a bacterium (though spelled procaryote and eucaryote there).

[47] That paper cites Édouard Chatton's 1937 book Titres et Travaux Scientifiques[48] for using those terms and recognizing the distinction.

[47] In 1977, Carl Woese proposed dividing prokaryotes into the Bacteria and Archaea (originally Eubacteria and Archaebacteria) because of the major differences in the structure and genetics between the two groups of organisms.

Archaea were originally thought to be extremophiles, living only in inhospitable conditions such as extremes of temperature, pH, and radiation but have since been found in all types of habitats.

Prokaryote ribosomes are smaller than those in eukaryote cytoplasm, but similar to those inside mitochondria and chloroplasts, one of several lines of evidence that those organelles derive from bacteria incorporated by symbiogenesis.

[55] In addition, many important genes of prokaryotes are stored in separate circular DNA structures called plasmids.

[65] The non-bacterial group comprising Archaea and Eukaryota was called Neomura by Thomas Cavalier-Smith in 2002, on the view that these form a clade.

[66] Unlike the above assumption of a fundamental split between prokaryotes and eukaryotes, the most important difference between biota may be the division between Bacteria and the rest (Archaea and Eukaryota).

[64] DNA replication differs fundamentally between the Bacteria and Archaea (including that in eukaryotic nuclei), and it may not be homologous between these two groups.

[68] Further, ATP synthase, though homologous in all organisms, differs greatly between bacteria (including eukaryotic organelles such as mitochondria and chloroplasts) and the archaea/eukaryote nucleus group.

[67] A ribonucleoprotein world has been proposed based on the idea that oligopeptides may have been built together with primordial nucleic acids at the same time, which supports the concept of a ribocyte as LUCA.

Diagram of a prokaryotic cell, a bacterium with a flagellum
Bacterial conjugation using F-pili to exchange DNA [ 16 ]
Biofilm of golden hydrophobic bacteria in a cave [ 24 ]
The bright colors of Grand Prismatic Spring , Yellowstone National Park are produced by thermophilic bacteria. [ 33 ]
Diagram of the origin of life with the Eukaryotes appearing early, not derived from prokaryotes, as proposed by Richard Egel in 2012. This view, one of many on the relative positions of prokaryotes and eukaryotes, would imply that the universal common ancestor was relatively large and complex. [ 38 ]
Phylogenetic tree showing the diversity of prokaryotes. [ 46 ]
Phylogenetic tree showing the diversity of prokaryotes. [ 64 ] This 2018 proposal shows eukaryotes within the archaean Asgard group which represents a modern version of the eocyte hypothesis . In this view, the division between bacteria and the rest is what groups organisms into the two major domains.