Pyrodictium gen. nov., a New Genus of Submarine Disc-Shaped Sulphur Reducing Archaebacteria Growing Optimally at 105°C.

Summary Six isolates of a new genus of anaerobic archaebacteria, named Pyrodictium , were isolated from a submarine solfataric field off Vulcano, Italy. These disc-shaped organisms grew at at least 110°C with an optimum around 105°C, and formed highly unusual networks of fibres. They were hydrogen-sulphur-autotrops. During growth in a fermenter, pyrite was formed. Two species can be distinguished: Pyrodictium occultum — which has a G + C-content of 62 mol%, and, as the dominant component in its cell envelope, a glycoprotein with a molecular weight of 172000 — and Pyrodictium brockii — which has a G + C-content of 51.5 to 56.6 mol%, a protein of molecular weight 150000 as its major cell envelope component, and whose growth yield is greatly increased in the presence of yeast extract.