8.15F: Nanoarchaeum and Aciduliprofundum
- Discuss the unique characteristics associated with Nanoarchaeum
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. It is a thermophile that grows in temperatures approaching boiling (80 degrees Celsius). Nanoarchaeum grows best in environments with a pH of six, and a salinity concentration of 2%. Nanoarchaeum cannot synthesize lipids but obtains them from its host, Ignicoccus. Nanoarchaeum appears to be an obligatory symbiont of this archaeon Ignicoccus, and must be in contact with it to survive.
Nanoarchaeum cells are only 400 nm in diameter, making it the next smallest known living organism to 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. N. equitans genome consists of a single circular chromosome, and lacks almost all genes required for 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. Nanoarchaeum 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. Genetically, Nanoarchaeum is peculiar in that its 16S RNA sequence is undetectable by the most common methods.
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).
Aciduliprofundum is another genus of the Euryarchaeota, though relatively less is known about it.
Key Points
- Nanoarchaeum grows best in environments with a pH of six and a salinity concentration of 2%.
- Nanoarchaeum cannot synthesize lipids but obtains them from its host, Ignicoccus.
- 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.
Key Terms
- nanobes : A tiny filamental structure that may or not be a living organism, and if living, would be the smallest form of life, 1/10 the size of the smallest known bacteria.