A new genus of methanogenic bacteria is described. The colonies produced by these bacteria are yellow, circular, and convex with lobate margins; an optical pattern of regular, light and dark striations throughout the colonies is a most unique and distinguishing characteristic. These striations are two cell lengths apart. Cells are gram negative and occur in filaments up to 100 μm in length. Tufts of polar flagella and a striated cell surface are revealed in electron micrographs; cell ends are blunt, not rounded. The deoxyribonucleic acid base composition of the type species is 45 mol% guanine plus cytosine. Formate or hydrogen and carbon dioxide serves as a substrate for methane formation and growth; acetate, pyruvate, methanol, ethanol and benzoate do not. The name Methanospirillum is proposed for this new genus of spiral shaped methanogenic bacteria. The type species, Methanospirillum hungatii sp. nov., is named in honor of R.E. Hungate. The type strain of M. hungatii is JF1 (ATCC 27890).
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