Nanoarchaeum equitans
| Nanoarchaeum | |
|---|---|
| |
| Scientific classification | |
| Domain: | |
| Phylum: | |
| Genus: | |
| Species: | N. equitans
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| Binomial name | |
| "Candidatus Nanoarchaeum equitans Huber et al. 2002" | |
Nanoarchaeum equitans is a species of tiny microbe, discovered in 2002 in a hydrothermal vent off the coast of Iceland by Karl Stetter. Since it grows in temperatures approaching boiling, it is considered to be a thermophile. Nanoarchaeum appears to be an obligatory symbiont on the archaeon Ignicoccus; it must be in contact with the host organism to survive. Its cells are only 400 nm in diameter, making it the next smallest known living organism, excepting possibly nanobacteria and nanobes, whose status as living organisms is controversial. Its genome is only 490,885 nucleotides long; the smallest non-viral genome ever sequenced next to that of Candidatus Carsonella ruddii.
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 obligatory parasitism (or symbiosis).
See also
References
- ^ Brochier, Celine; Gribaldo, S; Zivanovic, Y; Confalonieri, F; Forterre, P (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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- Huber, Harald (2002). "A new phylum of Archaea represented by a nanosized hyperthermophilic symbiont". Nature. 417 (6884): 63–67. doi:10.1038/417063a. PMID 11986665.
{{cite journal}}: Cite has empty unknown parameter:|month=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) (This paper represents the first discovery of Nanoarchaeum.) - Waters, Elizabeth (2003). "The genome of Nanoarchaeum equitans: insights into early archaeal evolution and derived parasitism". PNAS. 100 (22): 12984–12988. doi:10.1073/pnas.1735403100. PMC 240731. PMID 14566062.
{{cite journal}}: Cite has empty unknown parameter:|month=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) (This paper describes the genome sequence of Nanoarchaeum.) - Brochier, Celine; Gribaldo, S; Zivanovic, Y; Confalonieri, F; Forterre, P (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.
{{cite journal}}: Cite has empty unknown parameters:|month=and|coauthors=(help)CS1 maint: unflagged free DOI (link) (Recent work suggesting that Nanoarchaeum is not a new phylum of archaea, but is a type of euryarchaeon.) - Das, Sabyasachi (2006). "Analysis of Nanoarchaeum equitans genome and proteome composition: indications for hyperthermophilic and parasitic adaptation". BMC Genomics. 7: 186. doi:10.1186/1471-2164-7-186. PMC 1574309. PMID 16869956.
{{cite journal}}: Cite has empty unknown parameter:|month=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help)CS1 maint: unflagged free DOI (link) (This paper describes the genome and proteome analysis of Nanoarchaeum.)