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Nanoarchaeum equitans

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Nanoarchaeum equitans

On the basis of the small subunit of ribosomal RNA, Nanoarchaeum equitans was identified as a new phylum of Archaea. In the identification of N. equitans, difficulties were already identified because the probes normally used to amplify ribosomal RNA turned out to be ineffectual in amplifying the rRNA of N. equitans. Furthermore, its rRNA sequence was unique and singular among the Archaea although it presented some secondary structures typical of Archaea. When its genome was sequenced it became clear that N. equitans presented a truly unusual set of characters. Firstly, the large number of split genes: at least eleven proteins are split in N. equitans, i.e. a protein such as alanyl-tRNA synthetase, which is normally codified in a single gene is, in N. equitans, codified in two completely different ge nes. Coherently, six tRNAgenes are split in the sense that the tRNA molecule, which is normally codified in a single gene, is codified in N. equitans in two genes codifying only half of the tRNA molecule and located in non-contiguous sites on its genome. Consistent with these first two characteristics of the genome of N. equitans

is the observation of the almost total absence of conserved operons on its genome. For instance the super-operon of ribosomal proteins, which is conserved in all the Archaea and Bacteria, is almost totally absent in N. equitans and only few fragments are present. Therefore, N. equitans seems to be the only nearly operon-less prokaryote.

All these proprieties seem to be ancestral traits and therefore N. equitans might be one of branch deeper of the archaeal domain.

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Nanoarchaeum equitans

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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. It has been proposed as the first species in a new phylum. 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 GC-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 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, which provides structure and protection for the entire cell.

Genome

Mycoplasma genitalium (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 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.[1]

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).

See also

References

  1. ^ Brochier, Celine; Gribaldo, S; Zivanovic, Y; Confalonieri, F; et al. (2005). "Nanoarchaea: representatives of a novel archaeal phylum or a fast-evolving euryarchaeal lineage related to Thermococcales?". Genome Biology. 6 (5): R42. doi:10.1186/gb-2005-6-5-r42. PMC 1175954. PMID 15892870.
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Nanoarchaeum equitans: Brief Summary

provided by wikipedia EN

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. It has been proposed as the first species in a new phylum. 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 GC-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 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, which provides structure and protection for the entire cell.

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Wikipedia authors and editors
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wikipedia EN