Nanoarchaeum

Nanoarchaeum equitans
Nanoarchaeum equitans (and its host Ignicoccus)
Scientific classification
Domain:	Archaea
Phylum:	Nanoarchaeota
Order:	Nanoarchaeales
Family:	Nanoarchaeaceae
Genus:	Nanoarchaeum
Species:	N. equitans
Binomial name
Nanoarchaeum equitans Huber et al. 2002

Nanoarchaeum equitans is a species of marine Archaea that was discovered in 2002 in a hydrothermal vent off the coast of Iceland on the Kolbeinsey Ridge by Karl Stetter. Strains of this microbe were also found on the Sub-polar Mid Oceanic Ridge, and in the Obsidian Pool in Yellowstone National Park. Since it grows in temperatures approaching boiling, at about 80 degrees Celsius, it is considered to be a thermophile. It grows best in environments with a pH of 6, and a salinity concentration of 2%. Nanoarchaeum appears to be an obligate symbiont on the archaeon Ignicoccus; 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 one of the smallest known cellular organisms, and the smallest known archaeon.

N. equitans' genome consists of a single circular chromosome, and has an average G+C content of 31.6%. It lacks almost all of the genes required for the synthesis of amino acids, nucleotides, cofactors, and lipids, but encodes everything needed for repair and replication. A total of 95% of its DNA encodes for proteins for 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, which provides structure and protection for the entire cell.

Mycoplasma genitalium (size 0.58 Mbp, with 475 genes) was regarded as a cellular unit with the smallest genome size (in Mbp) until 2003 when Nanoarchaeum was sequenced (size 0.49 Mbp, with 540 genes).

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