Crenarchaeota

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Crenarchaeota
Sulfolobus, infected with the Sulfolobus virus STSV1 (ICTV: Sulfolobus spindle-shaped virus 1). Scale = 1 μm.

Sulfolobus , infected with the Sulfolobus virus STSV1 ( ICTV : Sulfolobus spindle-shaped virus 1 ).
Scale = 1  μm .

Systematics
Classification : Creature
Domain : Archaea ( Archaea )
Department : Crenarchaeota
Scientific name
Crenarchaeota
George M. Garrit & John G. Holt , 2002

The Crenarchaeota (from the Greek crenos , origin or source, outdated: eocytes, scientifically: Eocyta) are unicellular organisms and belong to the domain of the Archaea . In the past, the Crenarchaeota were only considered to be extremophiles (i.e. either (extremely) thermophilic or thermoacidophilic or psychrophilic ), but further studies showed that the Crenarchaeota are among the most common archaea in the sea. This group is known as the mesophilic marine group I Crenarchaeota.

properties

Within the Crenarchaeota one can find organisms that are adapted to extreme environmental conditions and can be found in areas with very high or very low temperatures. Many representatives live in the arctic plankton , where they often survive at temperatures below 0 ° C. However, these psychrophiles have only been cultivated in isolated cases under laboratory conditions (see also Psychrophilia and Cryophiles ). Another group within the Crenarchaeota lives under hyperthermal conditions, ie at temperatures of 80–110 ° C, Pyrolobus fumarii even lives at 113 ° C and survives even one hour of autoclaving . Many of the Crenarchaeota such as B. Sulfolobus acidocaldarius also tolerate high acid concentrations ( pH values of 1–2) and are therefore thermoacidophilic.

One of the best characterized organisms of the Crenarchaeota is Sulfolobus solfataricus . This organism was originally isolated from sulphurous hot springs in Italy and grows at 80 ° C and a pH value of 2-4.

Since there is often no organic substrate in their habitat, many live from the fixation of sulfur, carbon dioxide or hydrogen. However, others can also metabolize organic matter. In carbon dioxide assimilation, they use either the 3-hydroxypropionate / 4-hydroxybutyrate cycle (e.g. Sulfolobus) or the dicarboxylate / 4-hydroxybutyrate cycle (e.g. Desulfurococcales or Thermoproteales).

The representatives of the Crenarchaeota serve as hosts for the two virus families of the Ligamenvirales , the Rudiviridae and Lipothrixviridae .

Systematics

Internal system

External system

In the last few years (as of 2017), organisms have been identified based on genomes that are related to the Crenarchaeota. Initially, the following were found:

Together with the Crenarchaeota, they were temporarily classified in a so-called TACK supergroup (after the first letters of the Thaum, Aig, Cren and Korarchaeota). After this suggestion, further archaea from the environment of the Crenarchaeota were discovered:

These were also placed under the TACK super group. A separate Asgard supergroup was proposed for the following taxa :

For the then known representatives of these two supergroups, the name Proteoarchaeota (also Proteoarchaea) was proposed as a comprehensive taxonomic unit . The Proteoarchaeota thus include the entire supergroups TACK and Asgard (implicitly also their above new members).

Eocyte Hypothesis

The eocyte hypothesis proposed by James Lake in the 1980s suggests that eukaryotes (cells with a complex structure and multicellular cells such as plants, fungi and animals, especially humans) developed from the prokaryotic eocytes (an old name for Crenarchaeota).

The V-type ATPase of the eukaryotes is similar to the A-type ATP synthase of the archaea - a fact that suggests an origin of the eukaryotes among the archaea. The similarities to the F-type ATP synthases found in bacteria , chloroplasts and mitochondria , on the other hand, are much smaller (the exceptional occurrence of the F-type in some archaeal lines and the A-type in some bacterial lines is seen as a result of horizontal gene transfer ).

An indication of a close relationship between Crenarchaeota and eukaryotes is the presence of a homologue of the RNA polymerase subunit Rbp-8 in Crenarchaeota, which is not found in the Euryarchaeota .

Since the discovery of other archaea groups related to the Crenarchaeota within the supergroup TACK, it has been speculated whether they might be even closer to the eukaryotes than they are. With the discovery of the TACK sister group Asgard, representatives of the archaea were found that are much closer to the eukaryotes; the eukaryotes may even have emerged from them. These results confirm and substantiate the statement of the endosymbiont theory with regard to the origin of the original karyotes , even if the relationships are still being discussed in detail.

Web links

Individual evidence

  1. ↑ Brock: Biology of Microorganisms. 11th edition. Prentice Hall, 2005, ISBN 0-13-144329-1 .
  2. ↑ W. Zillig et al. : The Sulfolobus "Caldariellard" group: Taxonomy on the basis of the structure of DNA-dependent RNA polymerases. In: Arch. Microbiol. 125 (3) 1980, pp. 259-269, doi: 10.1007 / BF00446886 .
  3. ^ IA Berg et al. : Autotrophic carbon fixation in archaea. In: Nat Rev Microbiol . 8, 2010, PMID 20453874 , pp. 447-460, doi: 10.1038 / nrmicro2365 .
  4. ^ Céline Brochier-Armanet, Bastien Boussau, Simonetta Gribaldo, Patrick Forterre: Mesophilic crenarchaeota: Proposal for a third archaeal phylum, the Thaumarchaeota . In: Nature Reviews Microbiology . tape 6 , no. 3 , 2008, p. 245-252 , doi : 10.1038 / nrmicro1852 , PMID 18274537 .
  5. ^ NCBI taxonomy page on Archaea
  6. ↑ Petitjean, C., Deschamps, P., López-García, P., and Moreira, D .: Rooting the Domain archaea by phylogenomic analysis supports the foundation of the new kingdom proteoarchaeota. . In: Genome Biol. Evol. . 7, 2014, pp. 191-204. doi : 10.1093 / gbe / evu274 .
  7. ↑ (UCLA) The origin of the nucleus and the tree of life , UCLA via web archive of February 7, 2003
  8. ↑ E. Hilario E, J. P. Gogarten: Horizontal transfer of ATPase genes - the tree of life becomes a net of life . In: Bio Systems . 31, No. 2-3, 1993, pp. 111-119. doi : 10.1016 / 0303-2647 (93) 90038-E . PMID 8155843 .
  9. ↑ M. Kwapisz, F. Beckouët, P Thuriaux: Early evolution of eukaryotic DNA-dependent RNA polymerases . In: Trends Genet. . 24, No. 5, 2008, pp. 211-215. doi : 10.1016 / j.tig.2008.02.002 . PMID 18384908 .
  10. ↑ Katarzyna Zaremba-Niedzwiedzka et al. : Asgard archaea illuminate the origin of eukaryotic cellular complexity , in: Nature 541, pp. 353–358 of January 19, 2017, doi: 10.1038 / nature21031 .
  11. ↑ The term 'bacteria' is not entirely correct; the microbes considered are archaea or (according to some researchers) at least proto- eukaryotes different from the bacteria .