Methanothermus fervidus, sp. nov., a novel extremely thermophilic methanogen isolated from an Icelandic hot spring

Summary A rod-shaped extremely thermophilic methanogen is described, growing between 65 and 97 °C with an optimal temperature around 83 °C and a doubling time of 170 min. The GC-content of its DNA is 33 mol %. The isolated cell wall sacculus contains pseudomurein. The complex cell envelope exhibits two layers, each about 12 nm thick; the inner represents the pseudomurein sacculus and the outer a protein envelope. An enriched fraction of RNA polymerase does not react with antiserum against RNA polymerase from Metbanobacterium thermoautotrophicum , indicating that the isolate belongs to a new family, the Methanothermaceae , within the order Methanobacteriales . The new organism is named Methanothermus fervidus .