f Isolation and Characterization of a Thermophilic Marine Methanogenic Bacterium, Methanogenium thermophilicum sp. nov. †

A new species of thermophilic marine methanogenic bacteria is described. Cells of this species occurred as irregular cocci, singly or in pairs, and did not possess flagella. Colonies were translucent, beige in color, and circular with entire edges. Either formate or hydrogen and carbon dioxide could serve as a substrate for growth and methane formation, whereas ethanol, methanol, acetate, propionate, and pyruvate could not. The temperature for optimum growth was 55°C, with minimal growth below 37°C and an upper temperature limit of 65°C. The pH for optimum growth was 7.0. Sodium chloride was required for growth; the concentration for optimum growth was 0.20 M. The minimum generation time was 2.5 h. The deoxyribonucleic acid base composition was 59 mol% guanine plus cytosine. The name Methanogenium thermophilicum is proposed for this organism. The type strain is CR-1 (= ATCC 33837 = DSM 2373).