Ignicoccus is a genus of Archaea

Archaea

The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...

 living in marine hydrothermal vent

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...

s. They were discovered in Kolbeinsey

Kolbeinsey

Kolbeinsey is a small island off the northern coast of Iceland, north-northwest of the island of Grímsey. The island is the northernmost point of Iceland and lies north of the Arctic Circle...

 Ridge north 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...

 and in the Pacific Ocean (at 9 degrees N

9th parallel north

The 9th parallel north is a circle of latitude that is 9 degrees north of the Earth's equatorial plane. It crosses Africa, the Indian Ocean, South Asia, Southeast Asia, the Pacific Ocean, Central America, South America and the Atlantic Ocean....

, 104 degrees W

104th meridian west

The meridian 104° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole....

) in 2000 (Huber et al., 2000).

Systematics

According to the comparisons of 16S rRNA genes, Ignicoccus represents a new, deeply branching lineage within the family of the Desulfurococcaceae (Huber et al., 2002). Three species are known, Ignicoccus islandicus, Ignicoccus pacificus and Ignicoccus hospitalis. strain KIN4I.

Cell structure

The archaea of the genus Ignicoccus have tiny coccoid

Coccus

Coccus can be used to describe any bacterium that has a spherical shape. It is one of the three distinct types of bacteria shapes, the other two being bacillus and spirillum cells...

 cells with a diameter of about 2 µm, that exhibit a smooth surface, an outer membrane and no S-layer

S-layer

An S-layer is a part of the cell envelope commonly found in bacteria, as well as among archaea.It consists of a monomolecular layer composed of identical proteins or glycoproteins. This two-dimensional structure is built via self-assembly and encloses the whole cell surface. Thus, the S-layer...

.

They have a previously unknown cell envelope

Cell envelope

The cell envelope is the cell membrane and cell wall plus an outer membrane, if one is present.Most bacterial cell envelopes fall into two major categories: Gram positive and Gram negative. These are differentiated by their Gram staining characteristics....

 structure - a cytoplasmic membrane, a periplasmic space

Periplasmic space

The periplasmic space or periplasm is a space between the peptidoglycan cell wall and inner membrane of Gram-negative bacteria or the equivalent space outside the inner membrane of Gram-positive bacteria. It may constitute up to 40% of the total cell volume in Gram-negative species, and is...

 (with a variable width of 20 to 400 nm, containing membrane-bound vesicles), and an outer membrane (approximately 10 nm wide, resembling the outer membrane of gram-negative

Gram-negative

Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...

 bacteria). The latter contains numerous tightly, irregularly packed single particles (about 8 nm in diameter) and pores with a diameter of 24 nm, surrounded by tiny particles, arranged in a ring (with a diameter of 130 nm) and clusters of up to eight particles (each particle 12 nm in diameter) (Rachel et al. 2002).

Physiology

Ignicocci live in a temperature range of 70-98 °C (optimum around 90 °C). They gain energy by reduction of elemental 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...

 to hydrogen sulfide

Hydrogen sulfide

Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

 using molecular hydrogen as the electron donor

Electron donor

An electron donor is a chemical entity that donates electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process....

 (Huber et al., 2002). A unique symbiosis with (or parasitism by) nanoarchaea

Nanoarchaeum

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...

has also been reported (Huber et al., 2002).