Nanoarchaeum
Encyclopedia
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 nanobe
s, 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 frame
s 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 obligatory parasitism (or symbiosis).
Hydrothermal vent
A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. Hydrothermal vents exist because the earth is both...
off the coast of Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
by Karl Stetter
Karl Stetter
Karl Otto Stetter is a German microbiologist and authority on astrobiology. He is an expert on microbial life at high temperatures.-Career:...
. Since it grows in temperatures approaching boiling, it is considered to be a thermophile
Thermophile
A thermophile is an organism — a type of extremophile — that thrives at relatively high temperatures, between 45 and 122 °C . Many thermophiles are archaea...
. Nanoarchaeum appears to be an obligatory symbiont
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
on the archaeon
Archaea
The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
Ignicoccus
Ignicoccus
Ignicoccus is a genus of Archaea living in marine hydrothermal vents. They were discovered in Kolbeinsey Ridge north of Iceland and in the Pacific Ocean in 2000 .-Systematics:...
; it must be in contact with the host organism to survive. Its cells are only 400 nm
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
in diameter, making it the next smallest known living organism, excepting possibly nanobacteria
Nanobacterium
Nanobacterium is the unit or member name of a proposed class of living organisms, specifically cell-walled microorganisms with a size much smaller than the generally accepted lower limit size for life...
and nanobe
Nanobe
A nanobe is a tiny filamental structure first found in some rocks and sediments. Some scientists hypothesize that nanobes are the smallest form of life, 1/10 the size of the smallest known bacteria...
s, whose status as living organisms is controversial. Its genome is only 490,885 nucleotides long; the smallest non-viral genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
ever sequenced next to that of Candidatus Carsonella ruddii
Candidatus Carsonella ruddii
Candidatus Carsonella ruddii is an obligate endosymbiotic Gamma Proteobacterium; it has the smallest genome of any characterised bacteria....
.
Genetically, Nanoarchaeum is peculiar in that its 16S RNA
16S ribosomal RNA
16S ribosomal RNA is a component of the 30S subunit of prokaryotic ribosomes. It is approximately 1.5kb in length...
sequence is undetectable by the most common methods. Initial examination of single-stranded ribosomal RNA
Ribosomal RNA
Ribosomal ribonucleic acid is the RNA component of the ribosome, the enzyme that is the site of protein synthesis in all living cells. Ribosomal RNA provides a mechanism for decoding mRNA into amino acids and interacts with tRNAs during translation by providing peptidyl transferase activity...
indicated that the organism most likely belonged to the Archaea
Archaea
The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
domain. However, its difference from the existing phyla, Euryarchaeota
Euryarchaeota
In the taxonomy of microorganisms, the Euryarchaeota are a phylum of the Archaea.The Euryarchaeota include the methanogens, which produce methane and are often found in intestines, the halobacteria, which survive extreme concentrations of salt, and some extremely thermophilic aerobes and anaerobes...
and Crenarchaeota
Crenarchaeota
In taxonomy, the Crenarchaeota has been classified as either a phylum of the Archaea kingdom or a kingdom of its own...
, was as great as the difference between the phyla. Therefore, it was given its own phylum, called Nanoarchaeota
Nanoarchaeota
In taxonomy, the Nanoarchaeota are a phylum of the Archaea. This phylum currently has only one representative, Nanoarchaeum equitans.-External links:...
. However, another group (see References) compared all of the open reading frame
Open reading frame
In molecular genetics, an open reading frame is a DNA sequence that does not contain a stop codon in a given reading frame.Normally, inserts which interrupt the reading frame of a subsequent region after the start codon cause frameshift mutation of the sequence and dislocate the sequences for stop...
s 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
Cofactor (biochemistry)
A cofactor is a non-protein chemical compound that is bound to a protein and is required for the protein's biological activity. These proteins are commonly enzymes, and cofactors can be considered "helper molecules" that assist in biochemical transformations....
. 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
DNA replication
DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...
, transcription
Transcription (genetics)
Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...
, and translation
Translation (genetics)
In molecular biology and genetics, translation is the third stage of protein biosynthesis . In translation, messenger RNA produced by transcription is decoded by the ribosome to produce a specific amino acid chain, or polypeptide, that will later fold into an active protein...
. 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
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
is also in question. Nanoarchaeum lacks the ability to metabolize hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
for energy, as many thermophiles do. It does have five subunits of an ATP synthase
ATP synthase
right|thumb|300px|Molecular model of ATP synthase by X-ray diffraction methodATP synthase is an important enzyme that provides energy for the cell to use through the synthesis of adenosine triphosphate . ATP is the most commonly used "energy currency" of cells from most organisms...
as well as pathways for oxidative deamination
Deamination
Deamination is the removal of an amine group from a molecule. Enzymes which catalyse this reaction are called deaminases.In the human body, deamination takes place primarily in the liver, however glutamate is also deaminated in the kidneys. Deamination is the process by which amino acids are...
. 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
- ArchaeaArchaeaThe Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
- MycoplasmaMycoplasmaMycoplasma refers to a genus of bacteria that lack a cell wall. Without a cell wall, they are unaffected by many common antibiotics such as penicillin or other beta-lactam antibiotics that target cell wall synthesis. They can be parasitic or saprotrophic. Several species are pathogenic in humans,...
- IgnicoccusIgnicoccusIgnicoccus is a genus of Archaea living in marine hydrothermal vents. They were discovered in Kolbeinsey Ridge north of Iceland and in the Pacific Ocean in 2000 .-Systematics:...
- Candidatus Carsonella ruddiiCandidatus Carsonella ruddiiCandidatus Carsonella ruddii is an obligate endosymbiotic Gamma Proteobacterium; it has the smallest genome of any characterised bacteria....
, RickettsiaRickettsiaRickettsia is a genus of non-motile, Gram-negative, non-sporeforming, highly pleomorphic bacteria that can present as cocci , rods or thread-like . Being obligate intracellular parasites, the Rickettsia survival depends on entry, growth, and replication within the cytoplasm of eukaryotic host cells...
, and other ProteobacteriaProteobacteriaThe Proteobacteria are a major group of bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, and many other notable genera....