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''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. 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. ==Genome== Genetically, ''Nanoarchaeum'' is peculiar in that its 16S RNA sequence is undetectable by the most common methods. Initial examination of single-stranded ribosomal RNA indicated that the organism most likely belonged to the Archaea domain. However, its difference from the existing phyla, Euryarchaeota and Crenarchaeota, was as great as the difference between the phyla. Therefore, it was given its own phylum, called Nanoarchaeota. However, another group (see References) compared all of the open reading frames 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 nucleotides, amino acids, lipids, and cofactors. The cell most likely obtains these biomolecules from Ignicoccus. However, unlike many parasitic microbes, ''Nanoarchaeum'' has many DNA repair enzymes, as well as everything necessary to carry out DNA replication, transcription, and translation. This may explain why the genome lacks the large stretches of non-coding DNA characteristic of other parasites. The organism's ability to produce its own ATP is also in question. ''Nanoarchaeum'' lacks the ability to metabolize hydrogen and sulfur for energy, as many thermophiles do. It does have five subunits of an ATP synthase as well as pathways for oxidative deamination. 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). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nanoarchaeum equitans」の詳細全文を読む スポンサード リンク
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