Nanoarchaeota is a proposed phylum in the domain Archaea that currently has only one representative, Nanoarchaeum equitans, which was discovered in a submarine hydrothermal vent and first described in 2002.
Euryarchaeota is a kingdom of archaea. Euryarchaeota are highly diverse and include methanogens, which produce methane and are often found in intestines; halobacteria, which survive extreme concentrations of salt; and some extremely thermophilic aerobes and anaerobes, which generally live at temperatures between 41 and 122 °C. They are separated from the other archaeans based mainly on rRNA sequences and their unique DNA polymerase. The only validly published name for this group under the Prokaryotic Code is Methanobacteriati.
Methanosarcinales is an order of Archaea in the class Methanomicrobia, phylum Methanobacteriota. The order Methanosarcinales contains both methanogenic and methanotrophic lineages, although the latter have so far no pure culture representatives. Methanotrophic lineages of the order Methanosarcinales were initially abbreviated as ANME to distinguich from aerobic methanotrophic bacteria. Currently, those lineages receive their own names such as Ca. Methanoperedens, Ca. Methanocomedens (ANME-2a), Ca.Methanomarinus (ANME-2b), Ca. Methanogaster (ANME-2c), Ca. Methanovorans (ANME-3). The order contains archaeon with one of the largest genome, Methanosarcina acetivorans C2A, genome size 5,75 Mbp.
Archaeal Richmond Mine acidophilic nanoorganisms (ARMAN) were first discovered in an extremely acidic mine located in northern California (Richmond Mine at Iron Mountain) by Brett Baker in Jill Banfield's laboratory at the University of California Berkeley. These novel groups of archaea named ARMAN-1, ARMAN-2 (Candidatus Micrarchaeum acidiphilum ARMAN-2), and ARMAN-3 were missed by previous PCR-based surveys of the mine community because the ARMANs have several mismatches with commonly used PCR primers for 16S rRNA genes. Baker et al. detected them in a later study using shotgun sequencing of the community. The three groups were originally thought to represent three unique lineages deeply branched within the Euryarchaeota, a subgroup of the Archaea. However, based on a more complete archaeal genomic tree, they were assigned to a new superphylum named DPANN. The ARMAN groups now comprise deeply divergent phyla named Micrarchaeota and Parvarchaeota. Their 16S rRNA genes differ by as much as 17% between the three groups. Prior to their discovery, all of the Archaea shown to be associated with Iron Mountain belonged to the order Thermoplasmatales (e.g., Ferroplasma acidarmanus).
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 Nitrososphaerota are a phylum of the Archaea proposed in 2008 after the genome of Cenarchaeum symbiosum was sequenced and found to differ significantly from other members of the hyperthermophilic phylum Thermoproteota. Three described species in addition to C. symbiosum are Nitrosopumilus maritimus, Nitrososphaera viennensis, and Nitrososphaera gargensis. The phylum was proposed in 2008 based on phylogenetic data, such as the sequences of these organisms' ribosomal RNA genes, and the presence of a form of type I topoisomerase that was previously thought to be unique to the eukaryotes. This assignment was confirmed by further analysis published in 2010 that examined the genomes of the ammonia-oxidizing archaea Nitrosopumilus maritimus and Nitrososphaera gargensis, concluding that these species form a distinct lineage that includes Cenarchaeum symbiosum. The lipid crenarchaeol has been found only in Nitrososphaerota, making it a potential biomarker for the phylum. Most organisms of this lineage thus far identified are chemolithoautotrophic ammonia-oxidizers and may play important roles in biogeochemical cycles, such as the nitrogen cycle and the carbon cycle. Metagenomic sequencing indicates that they constitute ~1% of the sea surface metagenome across many sites.
Terrabacteria is a taxon containing approximately two-thirds of prokaryote species, including those in the gram positive phyla as well as the phyla "Cyanobacteria", Chloroflexota, and Deinococcota.
Bacterial phyla constitute the major lineages of the domain Bacteria. While the exact definition of a bacterial phylum is debated, a popular definition is that a bacterial phylum is a monophyletic lineage of bacteria whose 16S rRNA genes share a pairwise sequence identity of ~75% or less with those of the members of other bacterial phyla.
Saccharibacteria, formerly known as TM7, is a major bacterial lineage. It was discovered through 16S rRNA sequencing.
Nanohaloarchaea is a clade of diminutive archaea with small genomes and limited metabolic capabilities, belonging to the DPANN archaea. They are ubiquitous in hypersaline habitats, which they share with the extremely halophilic haloarchaea.
The "Aigarchaeota" are a proposed archaeal phylum of which the main representative is Caldiarchaeum subterraneum. It is not yet clear if this represents a new phylum or a Nitrososphaerota order, since the genome of Caldiarchaeum subterraneum encodes several Nitrososphaerota-like features. The name "Aigarchaeota" comes from the Greek αυγή, avgí, meaning "dawn" or "aurora", for the intermediate features of hyperthermophilic and mesophilic life during the evolution of its lineage.
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.
Parvarchaeota is a phylum of archaea belonging to the DPANN archaea. They have been discovered in acid mine drainage waters and later in marine sediments. The cells of these organisms are extremely small consistent with small genomes. Metagenomic techniques allow obtaining genomic sequences from non-cultured organisms, which were applied to determine this phylum.
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.
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.
The candidate phyla radiation is a large evolutionary radiation of bacterial lineages whose members are mostly uncultivated and only known from metagenomics and single cell sequencing. They have been described as nanobacteria or ultra-small bacteria due to their reduced size (nanometric) compared to other bacteria.
Heimdallarchaeota is a group of archaea that in turn forms a distinct group within the superphylum Asgard. Named after the mythical Norse god, Heimdall, one of the sons of Odin, it consist of several archaea that are considered as the closest relatives of eukaryotic organism. The first specimens were discovered from the marine sediments at Loki's Castle and Bay of Aarhus, and some other species from Auka hydrothermal vent field in the Pacific Ocean. Proposed as a phylum, it consists of a class Heimdallarchaeia, that contains at least three orders and three genera. Discovered by team of microbiologists at the Uppsala University, Sweden, led by Thijs Johannes Gerardus Ettema, and reported in 2017, Heimdallarchaeota is the group to which eukaryotes, or more specifically, from where the common ancestor of all eukaryotes emerged.
