Prokaryota

Cashiers
Temporary range: 4280–0Ma Had. Arcaico Proterozoic Fan. Physics – Recent
Procarotes.
Taxonomy
(without rank): Cytota Super Kingdom or Empire: Prokaryota Chatton 1925 emend. Swain 1969
Domains or kingdoms
Archaea Bacteria
Synonyms
Bacteria, Ehrenberg 1828 Moneres, Haeckel 1866 Schizophyta, Cohn 1875 Procaryotes, Chatton 1925 Akaryonta, Novák 1930 Akaryota, Forterre 1995 Archaiophyta, Vilhelm 1931 Plantae holoplastidae, Pascher 1931 Monera, Copeland 1938, Barkley 1939, 1949, Stanier & van Niel 1941, Whittaker 1959 Anucleobionta, Rothmaler 1948 Mychota sensu Barkley 1949, Copeland 1956 Protophyta sensu Krassilnikov, 1949 Akaryobionta, Rothmaler 1951 Archezoa sensu Copeland, 1956 prokaryon, Dougherty 1957 Prokaryonta, Fott 1959 (according to Round 1973) protocaryotes, Chadefaud 1960 Procaryota, Christensen 1962, Allsopp 1969 Procaryotae, Murray 1968 Procaryonta, Novák 1969 Prokaryota, Swain 1969, Fott 1971, Margulis 1974, Cavalier-Smith 1981, Mayr 1998, Ruggiero et al. 2015 Procytota, Jeffrey 1971 Prokarya, Margulis 1996

In biology, prokaryotes or prokaryotes (taxon Prokaryota) is the superkingdom or domain that includes microorganisms made up of prokaryotic cells, that is,, cells that have DNA dispersed in the cytoplasm, since there is no cell nucleus. The term derives from the Greek: πρό-(pro-), "before" + κάρυον (carion), "nut" or "almond", as a reference to the lack of a cell nucleus, The prokaryotes or prokaryotic organisms have received various names such as Bacteria, Monera and Schizophyta, depending on authors and classification systems. Other terms used were Mychota, Protophyta and Procaryotae. It is made up of two well-differentiated domains: Archaea and Bacteria.

Prokaryotes are unicellular, except for some cases such as myxobacteria, some of which have multicellular stages in their life cycle. In other cases they create large colonies, such as cyanobacteria. Prokaryotes are characterized by not having a cell nucleus, mitochondria or other organelles. Compartmentalization is also frequent in the prokaryotic world in the form of compartments, some delimited by proteins and others delimited by lipids. They are microorganisms that have a single chromosome called a nucleoid, their reproduction is asexual by binary fission, they have a great variety of metabolisms and there are species adapted to all types of environments, even the most extreme, calculating that there are approximately 5×10³⁰ prokaryotes in the world.

History

The first prokaryotic microorganisms were observed by Anton van Leeuwenhoek in 1683 using a single-lens microscope designed by himself and together with protozoa he called them animacles. The invention of the microscope left behind the & #34;speculation phase" and ushers in the "age of observation", which culminated in the mid-19th century in the "golden period" of microbiology.

Among some of the key historical moments, it can be mentioned that in 1859 Louis Pasteur, considered the father of microbiology, defined bacterial fermentation; in 1876 Robert Koch discovers the bacterial infection of malignant anthrax or anthrax, in 1884 the Gram stain is discovered and in 1910 Paul Ehrlich developed the first antibiotic to combat Treponema of syphilis. In 1936 H.A Barker identified methanogens, in 1967 Thomas D. Brock discovered extremophiles and in 1977 a team from the University of Illinois discovered the great divergence between archaea and bacteria thanks to the genetic study of ribosomal RNA (Balch et al. 1977) which constitutes part of the beginnings of molecular phylogeny, then finding the following relationships:

That same year (1977), Woese et al. laid the foundations of the three-domain system, which was contradicted by the eocyte hypothesis of Lake et al. (1984). In any case, both postulates are part of modern microbial phylogeny.

General characteristics

Cell structure of a typical procariot.

Comparison between the size of procariot organisms and that of other organisms and biomolecules.

Prokaryotes are almost always:

• Unicellular agencies.
• Osmotrophos, feeding by osmotic absorption.
• They have cellular wall (except for some exceptions such as endoparasites)
• They usually have a protein S layer.
• They have plasma membrane that surrounds the cytoplasm composed of phospholipids.
• They have a single circular chromosome located in a cytoplasm region called nucleoid (DNA is a circular strand).
• They do not present a cellular core.
• There are no membranous orgadules proper, although there may be specialized procarote compartments.
• It has asexual reproduction by binary fission (without complex mitosis)
• There may be procariot conjugation, i.e., transfer of genetic material among procariots.
• The procariot cytoskeleton consists of structural proteins, maintains the cellular form and intervenes in the process of division.
• Each ribosome has a size of 70S, which in turn is made up of a subunit greater than 50S (which contains RNA 23S and 5S) and a subunit less than 30S (with RNA 16S).
• Presence of operones and plasmids.
• There are no recognizable objects except ribosomes with electronic microscope. Although there are exceptions in some bacteria.

Prokaryotes have enormous differences from eukaryotes, such as the absence of organelles, the presence of smaller ribosomes, or differences in reproduction. But the most important difference lies in the very origin of eukaryotes (eukaryogenesis), which would have a later and more complex evolutionary history as a result of the symbiotic association between different prokaryotic organisms. Mitochondria and chloroplasts synthesize their own ribosomes and these are also the same size as prokaryotes. This would prove the prokaryotic origin of these organelles by serial endosymbiosis. Thus, while prokaryotes originated about 3.5 billion years ago, eukaryotes appear much later, about 1.4 billion years ago and as descendants of prokaryotic organisms. From this point of view, we can consider Prokaryota as a paraphyletic group..

For a comparison with eukaryotic characteristics, see: Comparison table.

Size

They are typically between 1 and 7 μm in length and 0.2–2.0 µm in diameter, although they can go to extremes such as nanoarchaea and ultra-small bacteria, which are typically 0.4 µm (400 nanometers) in diameter. length and 0.25 µm in diameter. There are spirochetes that can reach 500 μm in length, but the largest bacterium is the proteobacterium Thiomargarita with 750 μm.

Organelles

In general, prokaryotes do not have any organelles. However, there are exceptions, since in certain cases there are membranous bodies that demonstrate the formation of prokaryotic cell compartments and that this is not an exclusive phenomenon of eukaryotes.

Some examples are the magnetosomes of magnetotactic bacteria such as Magnetospirillum, the carboxysomes of some CO₂ fixing bacteria, the chlorosomes in some phototrophic bacteria, the thylakoids in cyanobacteria, and fundamentally several types of compartments in planctomycetes such as the anammoxosome, riboplasm, parifoplasm and a nucleoid that is sometimes wrapped in a double membrane.

Metabolism

Prokaryotic metabolism is highly diversified. While eukaryotes have only two (animal and plant), prokaryotes have evolved in a wide variety of environments, so they depend on the following requirements:

Power source:

• Fototrophos, which require light
• Quimotrophos, which depend on chemical reactions

Carbon source:

• Atrophos or synthetics, using CO2
• Heterotrophos, which need organic compounds

Reducing source or donor of hydrogen and electrons:

• Lithophos, if your source is inorganic
• Organotrophos, if their source is organic

Nutritional types

The combination of the different metabolic factors in the previous paragraph gives rise to the following types of prokaryotes:

• Photolitootrophos: O photosynthetics, they were probably the first procariots, since as plants only require water, light and CO₂. Among them are the cyanobacteria, the green sulfur and non-sulfuric bacteria, the purple sulfur bacteria, and part of the non-sulphorous. Cyanobacteria (such as plants) also perform oxygenic photosynthesis, instead the green and purple bacteria perform anoxygenic photosynthesis.

• Photoorganoautrophos: They require light, CO₂ and organic acids, such as some non-sylfuric purpure bacteria.

• Photoorganotrophos: They require light and organic compounds, such as heliobacteria, some non-sulfuric bacteria and halophile arches.

• Chemolitoautrophos: O chemosynthetics, require energy from the oxidation of inorganic substances, in addition to CO₂, H₂ and many times NH₄+, as in the oxidizing bacteria of Fe, H, S and N, nitriphic bacteria (such as Nitrosomonas), methanogenous arches (euriots), nitriphic arches (taumarcheots), bleached sulfur bacteria (such as Acidithiobacillus), aquatic bacteria and sulfurous arches (crenota).

• Chemolitoheterotrophos: Oxidan inorganic compounds, but cannot fix CO₂like some H oxidant bacteria.

• Chemoorganotrophos. They feed on organic compounds (as animals and fungi do). They are the vast majority of bacteria and partly in metanogenic arches and other arches.

Breathing

The type of bacterial breathing can be identified, observing growth in a liquid medium of cultivation:
1. Aerobio
2. Anaerobic strict
3. Optional
4. Microaerophile
5. Anaerobic aerotolerant

Anaerobic respiration is diverse and archaic, instead of oxygen it generally uses an inorganic substance as an acceptor such as nitrate, sulfur, sulfate, thiosulfate, CO2, Fe+3, Mn+4, selenate, arsenate, and rarely a substance organic as fumarate, DMSO, TMAO or chlorobenzoate. Depending on their respiration, prokaryotes can be:

• Anaerobics, which use anaerobic breathing or fermentation of organic substances. As they can tolerate or not the presence of oxygen are called anaerobic aerotolerants or strict anaerobics, respectively.
• Aerobicsthat use aerobic breath (of O₂).
• MicroaerophilesThey use very little oxygen.
• Optional (called aerobics or optional anaerobics), breathing₂, but when found in a medium without oxygen use fermentation.

Heterotrophic organisms generally have aerobic metabolism (they breathe oxygen); and since the oxidation of glucose and other substances releases much more energy than their anaerobic use, aerobic beings soon became the dominant organisms on Earth because of the greater energy obtained with this type of respiration.

Environmental factors

Development temperature

Unlike eukaryotes, prokaryotes have great variability of habitats and temperature ranges for their development. Depending on their optimum development temperature, they can be:

• Psychotrophiles: From -1.8 °C to 20 °C
• Mesophiles: 20 to 40 °C
• Thermophiles: 40 to 70 °C
• Hyperthermals: 70 to 105 °C or more.

Extreme conditions

Adapting to different habitats on Earth has allowed prokaryotic organisms to evolve even in the most extreme environments. Depending on the environment in which they are developed, the following terms are used:

• Acidófilo: They develop in acidic media like Lactobacillus the yogurt. Thermoaccidophils such as sulfolobal arches in oceanic hydrothermal sources require pH 1.5-4 and temperature 65-90 °C.
• Alcalófilo: They develop in alkaline media with pH between 8.5 and 11, as some bacilos.
• Halophile: It requires a saline medium as in the oceans with 6% salt. Hyperhalophilal arches such as halobacteria require 12 to 23% on average or more.
• Barophile or piezophile: It requires high pressure like that of ocean funds. For example: Halomonas titanicae.
• Radiophile or radioresistent: It tolerates ionizing radiation very well like archaea Thermococcus gammatolerans.
• Endolito: He lives inside the rocks.
• Hippolyte: He lives under the rocks, like some cyanobacteria of cold weather.
• Metaloresistente: Living in environments with heavy metals such as iron, copper, zinc, cadmium and even arsenic such as chrysogenetes that breathe arseniato.
• Oligotrophe: That requires very few nutrients, which must have helped the proliferation of nutrients Pelagibacter in the marine bacterioplankton.
• Polyextremophile: Multiple Extremophile as Deinococcuswhich tolerates good heat, cold, dehydration, acidity, vacuum and high radiation.

Origin and evolution

The first living organisms may have been prokaryotes related to the origin of life (abiogenesis). The last universal common ancestor (LUCA) would be a prokaryotic cellular organism evolved from protobionts (proto-cells).

Statistical models confirm that all living things descend from a single universal ancestor. This is supported by evidence for the universality of the genetic code and of the cell as a basic biological unit. However, there is no agreement on the structural and/or metabolic characteristics of this universal ancestor, since there are various hypotheses that it could have been a progenote (RNA world hypothesis), a Gram positive bacterium, a Gram negative bacterium photosynthetic, or, perhaps more likely, a chemosynthetic, hyperthermophilic, archaean prokaryotic organism.

Antiquity

Palaeontological evidence dates the earliest prokaryotic organisms to at least 3.5 billion years (Ma), in the Eoarchean era. Fossil footprints reveal early life in terrestrial hot springs found in the Pilbara, Australia), also giving 3,500 Ma. The discovery of biogenic graphite in metasedimentary rocks in southwestern Greenland, constitutes evidence of 3,700 Ma old; although these findings have been disputed. Microfossils in the form of iron oxide microfilaments found at northern Canada, would be evidence of prokaryotic activity in marine hydrothermal vents dated between 3,770 and 4,280 Ma, which could indicate that life appeared relatively soon after the formation of the Earth.

A hot past

The first thermophile procarotes discovered were arches and bacteria in the thermal waters of Yellowstone in the late 1960s.

The most accepted theories indicate that the first living beings were prokaryotes that inhabited a hot ocean (primordial soup theory) or in volcanic hydrothermal vents in the darkness of the ocean floor (iron-sulfur world theory), where there is a hot, high-pressure, anaerobic medium, with the presence of CO₂ and sulfur compounds, a suitable medium for primordial chemosynthetic metabolism.

Evidence in this regard is found in prokaryotic phylogeny: According to bacterial phylogeny based on 16S, 23S rRNA, as well as some protein and enzymatic trees, the most divergent bacteria are thermophiles such as Thermotogae, Aquificae, Thermodesulfobacteria and dictyoglomi. In archaea it is more notorious, since most of the phyla have thermophilic members. Consistent with the phylogeny of the two main archean phyla, Crenarchaeota and Euryarchaeota, the most divergent subgroups are highly hyperthermophilic; in the first case it is the Pyrodictiaceae, whose optimum growth temperature is above 100 °C, and in the second it is Methanopyrus, a methanogen capable of surviving and reproducing at 122 °C.

The first living beings were prokaryotes and their appearance coincides approximately with the beginning of the Archaic period. At this time, the Earth's heat flux was nearly three times higher than it is today, volcanic activity was considerably higher, with numerous hot spots, rifts, mid-ocean ridges, and very hot eruptive lavas such as komatite, unusual today. The luminosity of the Sun was less than today, but at this time there was the greatest volume of greenhouse gases that acidified the oceans due to the dissolution of carbon dioxide. More than 90% of the Earth's surface was occupied by the oceans and its waters had a temperature of 70 °C. The Earth was still prey to the late intense bombardment of large meteorites until 3,200 Ma ago. All these conditions mean that only extremophiles survive..

During those remote times, the atmosphere and oceans lacked oxygen, so the predominant prokaryotic respiration was anaerobic; and photosynthesis must have been anoxygenic (no oxygen production) just as green and purple bacteria currently do. The oldest stromatolites of proven microbiological origin are 2,724 million years old.

Oxygenation of the Earth

Gradually the Earth cooled down, and a crucial event and probably the most important in prokaryotic evolution occurs during the Proterozoic 2.45 billion years ago, when the Great Oxidation Process began due to the accumulation of oxygen in the atmosphere and oceans, and the first glaciation appeared 2,300 Ma. Oxygenation was caused by the proliferation of cyanobacteria (blue-green algae), which are oxygenic photosynthetics and produced stromatolites with a maximum development about 1,200 million years ago. environment, the first eukaryotic beings appear about 1400 Ma, from prokaryotic ancestors. These changes must have meant a prokaryotic mass extinction, where thermophiles would only survive in hot springs or evolved to adapt to new habitats. From then until today, aerobic bacteria become the most abundant organisms on Earth.

Classification

Archaea and Bacteria

Broad consensus divides Prokaryota into two major groups: Archaea and Bacteria. Both are very old, dating back to the Archean, at the dawn of Earth's history, more than 3.5 billion years ago.

Their main differences are the following:

According to the three-domain system, Archaea and Bacteria are groups comparable to Eukarya, however, it must be taken into account that the eukaryotic origin is much later and was produced by symbiogenesis between an archaea and a bacterium, therefore that in addition to their own characteristics, eukaryotes have inherited characteristics related to nuclear DNA, histones, ribosomes, and informational genes from archaea, while from bacteria they have inherited characteristics related to cell membrane, metabolism, mitochondria, and operational genes.

Prokaryotic phylogeny and its relationship with eukaryotes

Procarotes have traditionally been regarded as precursors to eukaryotes. This changed when C. Woese postula based on the analysis of RNA 16S/18S, the great divergence between arches, bacteria and eukaryants, which constitutes the system of three domains, where they would relate as follows: Bacteria Archaea Eucarya This result shows that there would be greater proximity between Archaea and Eucarya, which has had backing in some phylogenetic trees of the genome, and others related to ARNP and RNAt.

Tree of life according to the analysis of the RNA of the lower subunit of the ribosomes.

However, in some proteome trees the relationship differs as follows:

Studies on the eukaryotic origin (eukaryogenesis), showed that the relationship with prokaryotes is not as simple as in these schemes. At least three prokaryotic organisms would be involved in eukaryotic origin and evolution: an archaea would have been the anaerobic proto-eukaryotic cell (eocyte hypothesis), while a proteobacteria would have given rise to mitochondria and eukaryotic aerobic heterotrophic metabolism; Additionally, a cyanobacterium would give rise to chloroplasts and the photosynthetic metabolism of plants (serial endosymbiosis). This implies that there would have been only two primary domains: Archaea and Bacteria.

On the other hand, prokaryotic phylogeny presents a multitude of difficulties for the interpretation of molecular phylogenetic trees (see Bacterial phylogeny). This is due to horizontal genetic transfer, where evolutionary inheritance is disturbed by the mobilome (a large set of viruses, plasmids and other elements); in such a way that depending on the type of analysis, for example of a gene sequence, RNA or specific proteins, many different results are obtained. Even so, an approximate phylogenetic relationship can be shown, according to some authors, between the different archaean and bacterial groups and superphyla and their relationship with eukaryotes. A somewhat agreed phylogeny in the GTDB database and the Annotree and including eukaryotes is the following:

Viewed another way, prokaryotic evolution and its relationship to eukaryotes show that before we talk about a phylogenetic tree of life, we should talk about a "ring of life"; in where it would be observed that the prokaryotic ancestors that originated the first eukaryote, are an archaea of the Asgard clade that inherited the informational genes, while an Alphaproteobacteria inherited the operational genes. As we can see in the following image:

Philogenetic ring of life: Cladogram of the main filos and prokaryotes. Proteoarchaeota and TACK claws are close or related to eukaryants. Terrabacteria clay is based on protein studies and represents early adaptation to land habitat. Gracilicutes, PVC, FCB and Rhodobacteria claws are negative grams and have extensive backing in the phylogenetic analysis of RNAr 16S, 23S, proteins and gene sequences. Posibacteria is the group of positive Grams and is based on the structural, biochemical, evolutionary and phylogenic similarities of ribosome proteins.

Recent studies (2018) reveal the existence of an important group of nanobacteria called CPR, ultra-small bacteria that would be parasites or symbionts of other microorganisms. These appear in a basal position among the bacteria, as seen in the attached image. Similarly, ultrasmall archaea appear in a basal position under the name DPANN.

Historical background

During the 19th and 20th centuries, notable advances were made in microbiological knowledge. However, this did not mean advances in phylogeny and natural classification of prokaryotes. The classification of plants and animals was based on comparative anatomy and embryology, whereas bacteria lack morphological complexity, while at the same time they have enormous physiological diversity.

Bergey's handbook from the 1960s and 1970s opted to give unnatural, but reasonable, classifications, rather than speculate on continually changing phylogenies. Many specialists (Stanier, van Niel, Winogradsky) resigned themselves to accepting that a prokaryotic phylogenetic classification was impossible, despite the general acceptance that it is a monophyletic group and that it is related to the monophyletic origin of life. It was then concluded that the use of the Linnaean system with its Latin terminology and its phylogenetic implications should be avoided, since it had no support, recognizing ignorance of everything related to bacterial evolution; except in the identification of genus / species and it was recommended common names such as sulfur, photosynthetic, nitrogen-fixing bacteria (Ninogvossky, van Niel) and proposed four main groups: cyanophyceae, myxobacteria, spirochetes and eubacteria (Stanier, Donderoff & Adelberg 1963).

The revolutionary step in phylogenetics was taken in the 1970s thanks to advances in molecular biology, which made it possible to develop more reliable natural trees through genetic analysis.

For the prokaryotic genetic analysis, the molecular sequence of the 16S ribosomal RNA was chosen, giving as a result that the archaea, a recently discovered prokaryotic group, were genetically distant from the other prokaryotes, which is attributed to an ancient divergence (Balch 1977) highest.

Subsequent genetic analyzes at the proteome level have strengthened prokaryotic phylogeny by confirming the clear separation between Archeae and Bacteria (Sicheritz 2001).

History of nomenclature and classification systems

Here is the relationship between some notable groupings and prokaryotic classification systems:

Prokaryotic organisms have been considered successively within the animal kingdom (Bacteria), plant kingdom (Schizophyta), protista (Moneres) and then grouped within their own kingdom (Monera or Procaryote).

Bacteria

Ehrenberg coined the term Bacteria in 1828 from the Greek βακτήριον (bacterion) meaning little rod. His 1838 classification is the first of many that used bacterial morphology to define groups. In it he grouped bacteria into the Animal kingdom, distinguishing 5 genera:

• Bacterium: in allusion to the bats and defined as rigid bacilos.
• Vibrio: for the vibes, defined as flexible bacilos.
• Spirillum: the spirilos, defined as rigid spirals.
• Spirochaeta: the spirochetes, defined as flexible spirals, is the only group that currently remains a taxon.
• Spirodiscus: flattened spirals.

Other later classifications include, for example, Micrococcus (Cohn, 1872) for cocci or spherical bacteria and Chlamydobacteriaceae (Migula, 1895) for filamentous bacteria surrounded by the pod and known today as proteobacteria.

Schizomycetes and Schizophyta

In 1857, the German botanist Nageli rejected the idea that bacteria were animals and gave them the name Schizomycetes (splitting fungi), within the plant kingdom.

A more coherent classification for these organisms was made by Ferdinand Cohn, who in 1875 joined bacteria (Schizomycetes) with blue-green algae (Schizophyceae) into one group which he named Schizophyta within the Planta kingdom. Schizophyta comes from schizo=partition and phyta=plant, alluding to the way bacteria reproduce by binary division.

This same criterion is maintained in subsequent classifications such as that of Engler (1924), Wettstein (1934) and Krasilnikov (1958), the latter using the term Protophyta.

Money

In 1866, Haeckel created the order Moneres (from the Greek μονήρης/moneres=simple), within the lowest level of the kingdom Protista to group bacteria, but not including blue-green algae that they were like Cyanophyceae among the algae. He mentions that bacteria are unique because "...unlike other protists, they do not have a nucleus and are as different as a hydra is from a vertebrate or a simple alga from a palm tree". In 1904 he rectified in his Die Lebenswunder (The Wonders of Life) recognizing that Chromaceae (blue-green algae), lacking a nucleus, should be grouped into Moneres along with bacteria; he also suggested when observing chloroplasts, that plants must have evolved by symbiosis between a green cell with another non-green phagotrophic cell. Ideas about symbiosis at the end of the 19th century were not uncommon. For Haeckel, the activity of the moneras is reduced to the purely chemical process of their metabolism, in such a way that the difference between them and other beings whose cells have a nucleus, it is the largest in all respects, even larger than that between a monera and an inorganic crystal.

A New Kingdom (Prokaryote)

The term prokaryote (French procaryotes), as well as eukaryote, were coined by Chatton in 1925 to differentiate anucleated from nucleated microorganisms.

Around this time, the search for a natural classification for bacteria was seen. In 1927, the botanist Edwin Copeland argued that a plant kingdom that includes bacteria "is no more natural than a kingdom of stones". In 1938, his son Herbert Copeland proposed for them a kingdom of their own called Mychota on the grounds that they were "the relatively unmodified descendants of life that appeared on Earth, and that they are clearly distinguished from protists by the absence of nuclei".

In parallel, in 1939, Barkley created the kingdom Monera (Neolatin form of Haeckel's moneres) to group viruses and prokaryotes, subdividing it into two groups:Archeophyta for viruses (defined as the particles of primitive early life) and Schizophyta for blue-green algae and bacteria.

A kingdom consisting only of bacteria called Monera was supported by van Niel in 1941, Bergey's manual proposes the kingdom Protophyta in 1948 and in successive editions Monera or Procaryote. Other authors such as Whittaker (1969) and Margulis (1978-1996) also used the term Monera.

Although in the 1940s the moneras were defined by negative meanings, such as the lack of a nucleus, lack of sexual reproduction, lack of plastids and organelles, by the 1960s with the development of molecular biology and the electron microscope, prokaryotes are redefined in comparative cytology, biochemistry and physiology, in such a way that the divergence in cell structure that separates bacteria and blue-green algae from other cellular organisms (prokaryotes vs. eukaryotes) is recognized as the greatest evolutionary discontinuity known in the world until now.

From superkingdom to empire

R.G.E. Murray, of Bergey's Manual, furthered their phylogenetic taxonomic recognition in 1968 by proposing Procaryotae along with Eucaryotae as highest level taxa. The following year A. Allsop gives them the level of "superkingdom". Gunther Stent (1971) also proposes the superkingdom Prokaryota, Whittaker (1978) gives it the category of "domain", Margulis (1995) proposes the term Prokarya and finally Mayr (1998) and Cavalier-Smith (2004) acknowledge the Prokaryota "empire".

Taxonomy

There is currently no official taxonomic system or one that is supported by all microbiologists. Institutions dedicated to prokaryotic taxonomy include the International Committee on Systematics of Prokaryotes (ICSP), the Manuel de Bergey List of Prokaryotic Names (LPSN), the US National Center for Technology Information (NCBI), and the Catalog of Life (CoL).

NCBI

According to NCBI taxonomy there are two prokaryotic superkingdoms that are subdivided into groups as follows:

Col

A recent taxonomy (CoL system) that includes paraphyletic groups, classifies the superkingdom Prokaryota into the following kingdoms and subkingdoms:

• superrein Prokaryota
  • Archaea kingdom
    • Crenarchaeota edge (TACK)
    • Euriarchaeota
  • Kingdom Bacteria
    • subreino Negibacteria
    • Subrein Posibacteria