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The hydrogen hypothesis is a model proposed by William F. Martin and Miklós Müller in 1998 that describes a possible way in which the mitochondrion arose as an endosymbiont within a prokaryotic host in the archaea, giving rise to a symbiotic association of two cells from which the first eukaryotic cell could have arisen (symbiogenesis).
The last universal common ancestor (LUCA) is the hypothesized common ancestral cell from which the three domains of life, the Bacteria, the Archaea, and the Eukarya originated. The cell had a lipid bilayer; it possessed the genetic code and ribosomes which translated from DNA or RNA to proteins. The LUCA probably existed at latest 3.6 billion years ago, and possibly as early as 4.3 billion years ago or earlier. The nature of this point or stage of divergence remains a topic of research.
Loki's Castle is a field of five active hydrothermal vents in the mid-Atlantic Ocean, located at 73 degrees north on the Mid-Atlantic Ridge between Iceland and Svalbard at a depth of 2,352 metres (7,717 ft). When they were discovered in mid-July 2008, they were the most northerly black smoker vents known to science.
A prokaryote is a single-cell organism whose cell lacks a nucleus and other membrane-bound organelles. The word prokaryote comes from the Ancient Greek πρό (pró), meaning 'before', and κάρυον (káruon), meaning 'nut' or 'kernel'. In the two-empire system arising from the work of Édouard Chatton, prokaryotes were classified within the empire Prokaryota. However in the three-domain system, based upon molecular analysis, prokaryotes are divided into two domains: Bacteria and Archaea. Organisms with nuclei are placed in a third domain: Eukaryota.
Archaea is a domain of organisms. Traditionally, Archaea only included its prokaryotic members, but this sense has been found to be paraphyletic, as eukaryotes are now known to have evolved from archaea. Even though the domain Archaea includes eukaryotes, the term "archaea" in English still generally refers specifically to prokaryotic members of Archaea. Archaea were initially classified as bacteria, receiving the name archaebacteria, but this term has fallen out of use.
The eukaryotes constitute the domain of Eukaryota or Eukarya, organisms whose cells have a membrane-bound nucleus. All animals, plants, fungi, seaweeds, and many unicellular organisms are eukaryotes. They constitute a major group of life forms alongside the two groups of prokaryotes: the Bacteria and the Archaea. Eukaryotes represent a small minority of the number of organisms, but given their generally much larger size, their collective global biomass is much larger than that of prokaryotes.
The eocyte hypothesis in evolutionary biology proposes that the eukaryotes originated from a group of prokaryotes called eocytes. After his team at the University of California, Los Angeles discovered eocytes in 1984, James A. Lake formulated the hypothesis as "eocyte tree" that proposed eukaryotes as part of archaea. Lake hypothesised the tree of life as having only two primary branches: prokaryotes, which include Bacteria and Archaea, and karyotes, that comprise Eukaryotes and eocytes. Parts of this early hypothesis were revived in a newer two-domain system of biological classification which named the primary domains as Archaea and Bacteria.
The Magnetococcales were an order of Alphaproteobacteria, but now the mitochondria are considered as sister to the alphaproteobactera, together forming the sister the marineproteo1 group, together forming the sister to Magnetococcidae.
Lokiarchaeota is a proposed phylum of the Archaea. The phylum includes all members of the group previously named Deep Sea Archaeal Group, also known as Marine Benthic Group B. Lokiarchaeota is part of the superphylum Asgard containing the phyla: Lokiarchaeota, Thorarchaeota, Odinarchaeota, Heimdallarchaeota, and Helarchaeota. A phylogenetic analysis disclosed a monophyletic grouping of the Lokiarchaeota with the eukaryotes. The analysis revealed several genes with cell membrane-related functions. The presence of such genes support the hypothesis of an archaeal host for the emergence of the eukaryotes; the eocyte-like scenarios.
Proteoarchaeota is a proposed archaeal kingdom thought to be closely related and possibly ancestral to the Eukaryotes.
Hadesarchaea, formerly called the South-African Gold Mine Miscellaneous Euryarchaeal Group, are a class of thermophile microorganisms that have been found in deep mines, hot springs, marine sediments, and other subterranean environments.
"Candidatus Thorarchaeota", or simply Thorarchaeota, is a phylum within the superphylum Asgard archaea. The Asgard superphylum represents the closest prokaryotic relatives of eukaryotes. Since there is such a close relation between the two different domains, it provides further evidence to the two-domain tree of life theory which states that eukaryotes branched from the archaeal domain. Asgard archaea are single cell marine microbes that contain branch like appendages and have genes that are similar to eukarya. The asgard archaea superphylum is composed of Thorarchaeota, Lokiarchaeota, Odinarchaeota, and Heimdallarchaeota. Thorarchaeota were first identified from the sulfate-methane transition zone in tidewater sediments. Thorarcheota are widely distributed in marine and freshwater sediments.
TACK is a group of archaea, its name an acronym for Thaumarchaeota, Aigarchaeota, Crenarchaeota, and Korarchaeota, the first groups discovered. They are found in different environments ranging from acidophilic thermophiles to mesophiles and psychrophiles and with different types of metabolism, predominantly anaerobic and chemosynthetic. TACK is a clade that is sister to the Asgard branch that gave rise to the eukaryotes. It has been proposed that the TACK clade be classified as Crenarchaeota and that the traditional "Crenarchaeota" (Thermoproteota) be classified as a class called "Sulfolobia", along with the other phyla with class rank or order. After including the kingdom category into ICNP, the only validly published name of this group is kingdom Thermoproteati.
The Orthokaryotes are a proposed Eukaryote clade consisting of the Jakobea and the Neokaryotes. Together with its sister Discicristata it forms a basal Eukaryote clade. They are characterized by stacked Golgi, orthogonal centrioles, and two opposite posterior ciliary roots.
The Scotokaryotes (Cavalier-Smith) is a proposed basal Neokaryote clade as sister of the Diaphoretickes. Basal Scotokaryote groupings are the Metamonads, the Malawimonas and the Podiata. In this phylogeny the Discoba are sometimes seen as paraphyletic and basal Eukaryotes.
Ubiquitin-like proteins (UBLs) are a family of small proteins involved in post-translational modification of other proteins in a cell, usually with a regulatory function. The UBL protein family derives its name from the first member of the class to be discovered, ubiquitin (Ub), best known for its role in regulating protein degradation through covalent modification of other proteins. Following the discovery of ubiquitin, many additional evolutionarily related members of the group were described, involving parallel regulatory processes and similar chemistry. UBLs are involved in a widely varying array of cellular functions including autophagy, protein trafficking, inflammation and immune responses, transcription, DNA repair, RNA splicing, and cellular differentiation.
Asgard or Asgardarchaeota is a proposed superphylum belonging to the domain Archaea that contain eukaryotic signature proteins. It appears that the eukaryotes, the domain that contains the animals, plants, and fungi, emerged within the Asgard, in a branch containing the Heimdallarchaeota. This supports the two-domain system of classification over the three-domain system.
Christa Schleper is a German microbiologist known for her work on the evolution and ecology of Archaea. Schleper is Head of the Department of Functional and Evolutionary Biology at the University of Vienna in Austria.
The two-domain system is a biological classification by which all organisms in the tree of life are classified into two domains, Bacteria and Archaea. It emerged from development of knowledge of archaea diversity and challenges the widely accepted three-domain system that classifies life into Bacteria, Archaea, and Eukarya. It was preceded by the eocyte hypothesis of James A. Lake in the 1980s, which was largely superseded by the three-domain system, due to evidence at the time. Better understanding of archaea, especially of their roles in the origin of eukaryotes through symbiogenesis with bacteria, led to the revival of the eocyte hypothesis in the 2000s. The two-domain system became more widely accepted after the discovery of a large group (superphylum) of Archaea called Asgard in 2017, which evidence suggests to be the evolutionary root of eukaryotes, thereby making eukaryotes members of the domain Archaea.
(Candidatus) Verstraetearchaeota is a phylum in the domain of Archaea. Other valid names for this phylum are Nitrososphaerota and Thermoproteota, but it also has a number of non-valid synonyms. This phylum has not been cultured. This domain is capable of Methanogenesis.
References
- 1 2 Spang, Anja; Stairs, Courtney W.; Dombrowski, Nina; Eme, Laura; Lombard, Jonathan; Caceres, Eva F.; Greening, Chris; Baker, Brett J.; Ettema, Thijs J. G. (2019). "Proposal of the reverse flow model for the origin of the eukaryotic cell based on comparative analyses of Asgard archaeal metabolism". Nature Microbiology. 4 (7): 1138–1148. doi:10.1038/s41564-019-0406-9. ISSN 2058-5276. PMID 30936488.
- ↑ Albers, Sonja; Ashmore, Jonathan; Pollard, Thomas; Spang, Anja; Zhou, Jizhong (2022). "Origin of eukaryotes: What can be learned from the first successfully isolated Asgard archaeon". Faculty Reviews. 11: 3. doi: 10.12703/r-01-000005 . ISSN 2732-432X. PMC 8815363 . PMID 35174363.
- 1 2 Zaremba-Niedzwiedzka, Katarzyna; Caceres, Eva F.; Saw, Jimmy H.; Bäckström, Disa; Juzokaite, Lina; Vancaester, Emmelien; Seitz, Kiley W.; Anantharaman, Karthik; Starnawski, Piotr; Kjeldsen, Kasper U.; Stott, Matthew B.; Nunoura, Takuro; Banfield, Jillian F.; Schramm, Andreas; Baker, Brett J. (2017-01-19). "Asgard archaea illuminate the origin of eukaryotic cellular complexity". Nature. 541 (7637): 353–358. Bibcode:2017Natur.541..353Z. doi:10.1038/nature21031. ISSN 1476-4687. PMID 28077874. S2CID 4458094.
- ↑ Wu, Fabai; Speth, Daan R.; Philosof, Alon; Crémière, Antoine; Narayanan, Aditi; Barco, Roman A.; Connon, Stephanie A.; Amend, Jan P.; et al. (2022). "Unique mobile elements and scalable gene flow at the prokaryote-eukaryote boundary revealed by circularized Asgard archaea genomes". Nature Microbiology. 7 (2): 200–212. doi:10.1038/s41564-021-01039-y. ISSN 2058-5276. PMC 8813620 . PMID 35027677.
- ↑ "Researchers discover 'marvel microbes' explaining how cells became complex". EurekAlert!. Retrieved 2024-09-13.
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