"''

Candidatus In prokaryote nomenclature, ''Candidatus'' (Latin for candidate of Roman office) is used to name prokaryotic phyla that are well characterized but yet-uncultured. Contemporary sequencing approaches, such as 16S sequencing or metagenomics, provide m ...

'' Thorarchaeota", or simply Thorarchaeota, is a

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

within the superphylum Asgard archaea. The Asgard superphylum represents the closest

prokaryotic A prokaryote () is a Unicellular organism, single-celled organism that lacks a cell nucleus, nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek language, Greek wikt:πρό#Ancient Greek, πρό (, 'before') a ...

relatives of

eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

s. 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

archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...

l 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 Lokiarchaeota is a proposed phylum of the Archaea. The phylum includes all members of the group previously named Deep Sea Archaeal Group (DSAG), also known as Marine Benthic Group B (MBG-B). Lokiarchaeota is part of the superphylum Asgard contai ...

Odinarchaeota Asgard or Asgardarchaeota is a proposed superphylum consisting of a group of archaea that includes Lokiarchaeota, Thorarchaeota, Odinarchaeota, and Heimdallarchaeota. It appears the eukaryotes emerged within the Asgard, in a branch containin ...

, and

Heimdallarchaeota Asgard or Asgardarchaeota is a proposed superphylum consisting of a group of archaea that includes Lokiarchaeota, Thorarchaeota, Odinarchaeota, and Heimdallarchaeota. It appears the eukaryotes emerged within the Asgard, in a branch containin ...

. Thorarchaeota were first identified from the

sulfate-methane transition zone The sulfate-methane transition zone (SMTZ) is a zone in oceans, lakes, and rivers found below the sediment surface in which sulfate and methane coexist. The formation of a SMTZ is driven by the diffusion of sulfate down the sediment column and the d ...

in tidewater sediments. Thorarcheota are widely distributed in marine and freshwater sediments.

Discovery

Thorarchaeota were discovered by analyzing

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...

sediments obtained from the

White Oak River The White Oak River is a blackwater river, close to 48 mi (77 km) long, on the coastal plain of southeast North Carolina in the United States. It empties in the Atlantic Ocean. Course It rises in the White Oak Pocosin in northern Onslo ...

North Carolina North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia and So ...

. Estuaries are brackish bodies of water where fresh and marine water meet, providing a rich and unique area of nutrients. A PhD student at the

University of Texas The University of Texas at Austin (UT Austin, UT, or Texas) is a public research university in Austin, Texas. It was founded in 1883 and is the oldest institution in the University of Texas System. With 40,916 undergraduate students, 11,075 ...

discovered new characteristics of Thorarchaeota that live under sediment and with

anoxic The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...

properties. The graduate students further proved that the archaea aided in the degradation of organic matter, fixation of inorganic carbon, and the reduction of sulfur. Thorarchaeota genomes that were obtained from the marine appeared to have diversity in metabolic pathways with the potential of degrading and up taking proteins and carbohydrates.

Description

Thorarchaeota have not been cultured in a laboratory. What is known about Thorarchaeota has come from analyzing partial and near complete genomes. 3,029 proteins have been sequenced from the partial genomes. These genomes contain genes that suggest that Thorarchaeota may have the ability to degrade organic matter, suggesting a role in the

carbon cycle The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and Earth's atmosphere, atmosphere of the Earth. Carbon is the main component of biological compounds as well as ...

and an intermediate role in the sulfur cycle. Genes have been found for a near complete Wood-Ljungdahl pathway but lacked the genes for

formate dehydrogenase Formate dehydrogenases are a set of enzymes that catalyse the oxidation of formate to carbon dioxide, donating the electrons to a second substrate, such as NAD+ in formate:NAD+ oxidoreductase () or to a cytochrome in formate:ferricytochrome-b1 o ...

. This could be due to having incomplete genomes. Thorachaeota may use the

tetrahydromethanopterin Tetrahydromethanopterin (THMPT, ) is a coenzyme in methanogenesis. It is the carrier of the C1 group as it is reduced to the methyl level, before transferring to the coenzyme M. Tetrahydrosarcinapterin (THSPT, ) is a modified form of THMPT, wh ...

Wood-Ljungdahl pathway to reduce carbon dioxide. Thorarchaeota have genes for protein degradation and assimilation which include the genes

clostripain Clostripain (, ''clostridiopeptidase B'', ''clostridium histolyticum proteinase B'', ''alpha-clostridipain'', ''clostridiopeptidase'', ''Endoproteinase Arg-C'') is a proteinase that cleaves proteins on the carboxyl peptide bond of arginine. It wa ...

and gingipain. They also have genes for extracellular

peptidase A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the fo ...

s. These genes may suggest that the main carbon source for Thorarchaeota is proteins and peptides. Thorarchaeota sequenced partial genomes also have the genes for

glycolysis Glycolysis is the metabolic pathway that converts glucose () into pyruvate (). The free energy released in this process is used to form the high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH ...

present. They are missing the genes for

hexokinase A hexokinase is an enzyme that phosphorylates hexoses (six-carbon sugars), forming hexose phosphate. In most organisms, glucose is the most important substrate for hexokinases, and glucose-6-phosphate is the most important product. Hexokina ...

s, however they have the genes for

pyruvate kinase Pyruvate kinase is the enzyme involved in the last step of glycolysis. It catalyzes the transfer of a phosphate group from phosphoenolpyruvate (PEP) to adenosine diphosphate (ADP), yielding one molecule of pyruvate and one molecule of ATP. P ...

s and phosphoenolpyruvate synthase. The presence of the genes for these enzymes may play a role in the ability to adapt to different environmental conditions. Genes have been found for

nitrogen fixation Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...

in most samples containing the partial genomes however, no genes for the nitrite reduction catalyzing enzymes have been found. Some of the sequenced partial genomes have near complete Calvin-Benson-Bassham pathways and have been found to use type IV

RuBisCO Ribulose-1,5-bisphosphate carboxylase-oxygenase, commonly known by the abbreviations RuBisCo, rubisco, RuBPCase, or RuBPco, is an enzyme () involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is con ...

. While other phyla within the Asgard Superphylum use type III and type IV RuBisCO, none have the Calvin-Benson-Bassham pathway.

References

{{Taxonbar, from=Q27668676 Archaea phyla