Hadarchaeota
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Hadesarchaea, formerly called the South-African Gold Mine Miscellaneous Euryarchaeal Group, are a class of
thermophile A thermophile is an organism—a type of extremophile—that thrives at relatively high temperatures, between . Many thermophiles are archaea, though they can be bacteria or fungi. Thermophilic eubacteria are suggested to have been among the earl ...
microorganisms that have been found in deep mines, hot springs, marine sediments and other subterranean environments.


Nomenclature

These archaea were initially called South-African Gold Mine Miscellaneous Euryarchaeal Group (SAGMEG) after their initial site of discovery. The name ''Hadesarchaea'' was proposed by Baker et al. in 2016, a reference to the Greek god of the underworld.


Phylogeny

Previously, Hadesarchaea (or SAGMEG) were only known to exist through their distinctive phylogenetic position in the
tree of life The tree of life is a fundamental archetype in many of the world's mythological, religious, and philosophical traditions. It is closely related to the concept of the sacred tree.Giovino, Mariana (2007). ''The Assyrian Sacred Tree: A Hist ...
. In 2016, scientists using
metagenomic Metagenomics is the study of genetic material recovered directly from environmental or clinical samples by a method called sequencing. The broad field may also be referred to as environmental genomics, ecogenomics, community genomics or microb ...
shotgun sequencing In genetics, shotgun sequencing is a method used for sequencing random DNA strands. It is named by analogy with the rapidly expanding, quasi-random shot grouping of a shotgun. The chain-termination method of DNA sequencing ("Sanger sequencing ...
were able to assemble several near-full genomes of these archaea. It was shown that the genome of Hadesarchaea is approximately 1.5 Megabase pairs in size, which is about 0.5 Mbp smaller than most archaea. These archaea have not been successfully cultivated in the laboratory, but their metabolic properties have been inferred from the genomic reconstructions. Hadesarchaea may have evolved from a methanogenic ancestor based on the genetic similarity with other methanogenic organisms.


Taxonomy

* "Hadarchaeota" Chuvochina et al. 2019 McGonigle_et_al._2019;_"Stygia"_Adam_et_al._2017.html" ;"title="Hadesarchaeota" McGonigle et al. 2019; "Stygia" Adam et al. 2017">Hadesarchaeota" McGonigle et al. 2019; "Stygia" Adam et al. 2017** "Persephonarchaeia" corrig. Mwirichia et al. 2016 (MSBL-1) ** "Hadarchaeia" Chuvochina et al. 2019 Baker_et_al._2016.html" ;"title="Hadesarchaea" Baker et al. 2016">Hadesarchaea" Baker et al. 2016(SAGMEG) *** "Hadarchaeales" Chuvochina et al. 2019 **** "Hadarchaeaceae" Chuvochina et al. 2019 ***** "''Candidatus'' Hadarchaeum" Chuvochina et al. 2019 ****** "''Ca.'' H. yellowstonense" Chuvochina et al. 2019 ***** "''Candidatus'' Hadesarchaeum" Hua et al. 2019 ****** "''Ca.'' H. tengchongensis" Hua et al. 2019 ***** "''Candidatus'' Methanourarchaeum" Hua et al. 2019 ****** "''Ca.'' M. thermotelluricum" Hua et al. 2019


Habitat and metabolism

These microbes were first discovered in a gold mine in South Africa at a depth of approximately 3 km (2 mi), where they are able to live without oxygen or light. They were later also found in the White Oak River estuary in North Carolina and in
Yellowstone National Park Yellowstone National Park is an American national park located in the western United States, largely in the northwest corner of Wyoming and extending into Montana and Idaho. It was established by the 42nd U.S. Congress with the Yellowst ...
's Lower Culex Basin. These areas are approximately 70 °C (158 °F) and highly alkaline. Based on phylogenetic marker gene survey, Hadesarchaeota might be present in soils in ancient mining areas in East Harz region, Germany. The microbes have been found in other marine environments as well. Some of these areas include cold seep systems in the
South China Sea The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by the shores of South China (hence the name), in the west by the Indochinese Peninsula, in the east by the islands of Taiwan and northwestern Phi ...
. Hadesarchaea has been found to be a dominant member of the archaeal community in the area. These cold seeps contain gas hydrate bearing sediments in which microbes play a major role in biogeochemical cycling. It is believed that Hadesarchaea is involved the oxidation of
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
with water in this environment. Hadesarchaea have also been found in subseafloor habitats located in the
Guaymas Basin The Guaymas Basin is a marginal rift basin, the largest such basin in the Gulf of California. It consists of two axial troughs (northern and southern). The basin results from the activity of one of the several spreading centers in the Gulf. The ...
and Sonora Margin around the
Gulf of California The Gulf of California ( es, Golfo de California), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Bermejo''), is a marginal sea of the Pacific Ocean that separates the Baja C ...
. In addition to being present in marine sediments, mines, and hot springs, Hadesarchaea has been identified in the
gut microbiome Gut microbiota, gut microbiome, or gut flora, are the microorganisms, including bacteria, archaea, fungi, and viruses that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the gut ...
of certain fish species. The freshwater pufferfish (''
Tetraodon cutcutia ''Tetraodon'' is a genus in the pufferfish family (Tetraodontidae) found in freshwater in Africa. It is the type genus of the family and historically included numerous other species; several Asian species were only moved to the genera ''Dichotomy ...
''), native to India, Assam, Bihar, and
West Bengal West Bengal (, Bengali: ''Poshchim Bongo'', , abbr. WB) is a state in the eastern portion of India. It is situated along the Bay of Bengal, along with a population of over 91 million inhabitants within an area of . West Bengal is the fou ...
, was found to have Hadesarchaea present in their gut microbiome. Hadesarchaea was found to be in the second most abundant in the archaeal community of the freshwater pufferfish. This was found to be similar to community abundance found in the gut of carnivorous
Salmon Salmon () is the common name for several commercially important species of euryhaline ray-finned fish from the family Salmonidae, which are native to tributaries of the North Atlantic (genus ''Salmo'') and North Pacific (genus '' Oncorhy ...
and herbivorous
grass carp The grass carp (''Ctenopharyngodon idella'') is a species of large herbivorous freshwater fish in the family Cyprinidae, native to the Pacific Far East, with a native range stretching from northern Vietnam to the Amur River on the Sino-Russi ...
. While Hadesarchaea are found to be in such high abundance for these environments, it is not completely known how they influence the health and trophic level of these fish. Hadesarchaea are unique among known archaea in that they can convert
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
and water to
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
and oxygen, producing hydrogen as a by-product. From metagenome-assembled genome (MAG) data, Hadesarchaea possess genes associated with Wood-Ljungdahl carbon fixation pathway, methanogenesis and alkane metabolism. Hadesarchaeal genomes have also been reported to contain genes that enable them to metabolize sugars and amino acids in a heterotrophic lifestyle, and perform dissimilatory nitrite reduction to ammonium. Initial research suggests that these organisms are also involved in significant geochemical processes. Because of their relatively small genome, it is assumed that the genomes of Hadesarchaea have been subjected to genome streamlining, possibly as a result of nutrient limitation.


See also

* Archea * Microbiology * Fermentative hydrogen production *
Thermophiles A thermophile is an organism—a type of extremophile—that thrives at relatively high temperatures, between . Many thermophiles are archaea, though they can be bacteria or fungi. Thermophilic eubacteria are suggested to have been among the earl ...
*
Geysers A geyser (, ) is a spring characterized by an intermittent discharge of water ejected turbulently and accompanied by steam. As a fairly rare phenomenon, the formation of geysers is due to particular hydrogeological conditions that exist only in ...


References

{{Taxonbar, from=Q22952202 Euryarchaeota Thermophiles Alkaliphiles