Methanothermus fervidus is a species of methanogen. It is notable for being extremely thermophilic. Its cells are rod-shaped; its complex cell envelope exhibits two layers, each about 12 nm thick; the inner represents the pseudomurein sacculus and the outer a protein envelope. The type strain is Methanothermus fervidus Stetter 1982. The cells are motile, strictly anaerobic and stain Gram positive. They can grow at temperatures as high as 97 ðC. Strain V24S<sup>T</sup> can subsist on carbon dioxide and hydrogen alone. Its genome is 1,243,342 bp in length.