Ignicoccus
Ignicoccus is a genus of hyperthermophillic Archaea living in marine hydrothermal vents. They were discovered in samples taken at the Kolbeinsey Ridge north of Iceland, as well as at the East Pacific Rise in 2000.
Systematics
According to the comparisons of 16S rRNA genes, Ignicoccus represents a new, deeply branching lineage within the family of the Desulfurococcaceae.Three species are known: I. islandicus, I. pacificus and I. hospitalis strain KIN4I.
Cell structure
The archaea of the genus Ignicoccus have tiny coccoid cells with a diameter of about 2 μm, that exhibit a smooth surface, an outer membrane and no S-layer.They have a previously unknown cell envelope structure—a cytoplasmic membrane, a periplasmic space, and an outer membrane. The latter contains numerous tightly, irregularly packed single particles and pores with a diameter of 24 nm, surrounded by tiny particles, arranged in a ring and clusters of up to eight particles 12 nm in diameter each.
The two layers of membrane previously reported are actually a type of endomembrane system consisting of cytoplasmic protrusions. In I. hospitalis, these structures harbor the endosymbiotic archaeon Nanoarchaeum equitans.