''Nanoarchaeum equitans'' is a species of marine archaea that was discovered in 2002 in a

hydrothermal vent A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspo ...

off the coast of

Iceland Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its ...

on the Kolbeinsey Ridge by

Karl Stetter Karl Otto Stetter (born 16 July 1941) is a German microbiologist and authority on astrobiology. He is an expert on microbial life at high temperatures. Career Stetter was born in Munich and studied biology at the Technical University of Munich. ...

. It has been proposed as the first species in a new

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 ...

. Strains of this microbe were also found on the Sub-polar Mid Oceanic Ridge, and in the

Obsidian Pool Obsidian () is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. Obsidian is produced from felsic lava, rich in the lighter elements such as sili ...

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 ...

. Since it grows in temperatures approaching boiling, at about 80 degrees Celsius, it is considered to be a

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 ...

. It grows best in environments with a pH of 6, and a salinity concentration of 2%. ''Nanoarchaeum'' appears to be an

obligate symbiont Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasi ...

on the

archaeon 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 Archaebact ...

Ignicoccus ''Ignicoccus'' is a genus of hyperthermophillic Archaea living in marine hydrothermal vents. They were discovered in samples taken at the Kolbeinsey Ridge north of Iceland, as well as at the East Pacific Rise (at 9 degrees N, 104 degrees W) i ...

''; it must be in contact with the host organism to survive. ''Nanoarchaeum equitans'' cannot synthesize lipids but obtains them from its host. Its cells are only 400 nm in diameter, making it the smallest known living organism, and the smallest known archaeon. ''N. equitans'' genome consists of a single circular chromosome, and has an average

GC-content In molecular biology and genetics, GC-content (or guanine-cytosine content) is the percentage of nitrogenous bases in a DNA or RNA molecule that are either guanine (G) or cytosine (C). This measure indicates the proportion of G and C bases out ...

of 31.6%. It lacks almost all of the genes required for the synthesis of

amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

nucleotides Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules with ...

cofactors Cofactor may also refer to: * Cofactor (biochemistry), a substance that needs to be present in addition to an enzyme for a certain reaction to be catalysed * A domain parameter in elliptic curve cryptography, defined as the ratio between the order ...

, and

lipids Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids in ...

, but encodes everything needed for repair and replication. ''N. equitans'' contains several genes that encode proteins employed in recombination, suggesting that ''N. equitans'' can undergo

homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may ...

. A total of 95% of its DNA encodes for proteins or stable RNA molecules. ''N. equitans'' has small appendages that come out of its circular structure. The cell surface is covered by a thin, lattice-shaped

S-layer An S-layer (surface layer) is a part of the cell envelope found in almost all archaea, as well as in many types of bacteria. The S-layers of both archaea and bacteria consists of a monomolecular layer composed of only one (or, in a few cases, two) ...

, which provides structure and protection for the entire cell.

Genome

Mycoplasma genitalium ''Mycoplasma genitalium'' (''MG'', commonly known as Mgen) is a sexually transmitted, small and pathogenic bacterium that lives on the mucous epithelial cells of the urinary and genital tracts in humans. Medical reports published in 2007 and 2 ...

'' (580 Kbp in size, with 515 protein-coding genes) was regarded as a cellular unit with the smallest genome size until 2003 when ''Nanoarchaeum'' was sequenced (491 Kbp, with 536 protein-coding genes). Genetically, ''Nanoarchaeum'' is peculiar in that its

16S RNA 16 S ribosomal RNA (or 16 S rRNA) is the RNA component of the 30S subunit of a prokaryotic ribosome (SSU rRNA). It binds to the Shine-Dalgarno sequence and provides most of the SSU structure. The genes coding for it are referred to as 16S rRN ...

sequence is undetectable by the most common methods. Initial examination of single-stranded

ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from riboso ...

indicated that the organism most likely belonged to 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 Archaeba ...

domain. However, its difference from the existing

phyla Phyla, the plural of ''phylum'', may refer to: * Phylum, a biological taxon between Kingdom and Class * by analogy, in linguistics, a large division of possibly related languages, or a major language family which is not subordinate to another Phy ...

, "

Euryarchaeota Euryarchaeota (from Ancient Greek ''εὐρύς'' eurús, "broad, wide") is a phylum of archaea. Euryarchaeota are highly diverse and include methanogens, which produce methane and are often found in intestines, halobacteria, which survive extr ...

" and

Thermoproteota The Thermoproteota (also known as crenarchaea) are archaea that have been classified as a phylum of the Archaea domain. Initially, the Thermoproteota were thought to be sulfur-dependent extremophiles but recent studies have identified characteris ...

, was as great as the difference between the phyla. Therefore, it was given its own phylum, called "

Nanoarchaeota Nanoarchaeota (Greek, "dwarf or tiny ancient one") are a phylum of the Archaea. This phylum currently has only one representative, ''Nanoarchaeum equitans''. Taxonomy 53 marker proteins based GTDB 07-RS207 phylogeny. The currently accepted ...

". However, another group (see References) compared all of the

open reading frame In molecular biology, open reading frames (ORFs) are defined as spans of DNA sequence between the start and stop codons. Usually, this is considered within a studied region of a prokaryotic DNA sequence, where only one of the six possible readi ...

s to the other Archaea. They argue that the initial sample, ribosomal RNA only, was biased and ''Nanoarchaeum'' actually belongs to the "Euryarchaeota" phylum. The sequencing of the ''Nanoarchaeum'' genome has revealed a wealth of information about the organism's biology. The genes for several vital metabolic pathways appear to be missing. ''Nanoarchaeum'' cannot synthesize most

, and

. The cell most likely obtains these biomolecules from

. In particular, ''N. equitans'' lacks all of the genes that encode

purine Purine is a heterocyclic aromatic organic compound that consists of two rings ( pyrimidine and imidazole) fused together. It is water-soluble. Purine also gives its name to the wider class of molecules, purines, which include substituted purines ...

nucleotide Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecu ...

biosynthesis in other organisms.Brown AM, Hoopes SL, White RH, Sarisky CA. Purine biosynthesis in archaea: variations on a theme. Biol Direct. 2011 Dec 14;6:63. doi: 10.1186/1745-6150-6-63. PMID: 22168471; PMCID: PMC3261824 However, unlike many parasitic microbes, ''Nanoarchaeum'' has many DNA repair enzymes, as well as everything necessary to carry out

DNA replication In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritan ...

, transcription, and

translation Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...

. This may explain why the genome lacks the large stretches of

non-coding DNA Non-coding DNA (ncDNA) sequences are components of an organism's DNA that do not encode protein sequences. Some non-coding DNA is transcribed into functional non-coding RNA molecules (e.g. transfer RNA, microRNA, piRNA, ribosomal RNA, and regula ...

characteristic of other parasites. The organism's ability to produce its own ATP is also in question. ''Nanoarchaeum'' lacks the ability to metabolize

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

and

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...

for energy, as many thermophiles do. It does have five subunits of an

ATP synthase ATP synthase is a protein that catalyzes the formation of the energy storage molecule adenosine triphosphate (ATP) using adenosine diphosphate (ADP) and inorganic phosphate (Pi). It is classified under ligases as it changes ADP by the formation ...

as well as pathways for oxidative

deamination Deamination is the removal of an amino group from a molecule. Enzymes that catalyse this reaction are called deaminases. In the human body, deamination takes place primarily in the liver, however it can also occur in the kidney. In situations of ...

. Whether it obtains energy from biological molecules imported from ''Ignicoccus'', or whether it receives ATP directly is currently unknown. The genome and proteome composition of ''N. equitans'' are marked with the signatures of dual adaptation – one to high temperature and the other to obligate parasitism (or symbiosis).

References

* (This paper represents the first discovery of ''Nanoarchaeum''.) * (This paper describes the genome sequence of ''Nanoarchaeum''.) * (Recent work suggesting that ''Nanoarchaeum'' is not a new phylum of archaea, but is a type of euryarchaeon.) * (This paper describes the genome and proteome analysis of ''Nanoarchaeum''.)

External links

NCBI taxonomy page for Nanoarchaeota

Tree of Life Nanoarchaeota

MicrobeWiki page for Nanoarchaeum
{{Taxonbar, from=Q221936 Archaea Archaea described in 2002 Organisms living on hydrothermal vents

Genome

See also

References

Further reading

External links