monium salts and sub-optimal concentra- tions of other nutrients should be used; also, the reactions of the media should approach the limiting acidity for growth, and the in- cubation temperature should not exceed 22° C. Motility: After 24 hours, jirimary cul- tures on agar, in peptone water and in broth are non-motile whereas those on urea agar are actively motile. Source: Isolated from urine and from garden soil. Also found in sea water (Wood, loc. cit.). Habitat: Presumably widely distributed. Genus V. Methanococcu.s Kluyver and van Niel, 1936, emend. Barker, 1936* (Kluyver and van Niel, Zent. f. Bakt., II Abt., 9J^, 1936, 400; Barker, Arch. f. Mikrobiol., 7, 1936, 430.) Me.tha.no.coc'cus. Gr. noun methy wine; M.L. noun methanum methane; Gr. noun coccus a berry; M.L. noun coccus a spherical cell; M.L. mas.n. Methanococcus methane coccus. Spherical cells, occurring singly, in pairs, or in masses. Motile or non-motile. Gram- variable. Chemo-heterotrophic, fermenting various organic compounds with the production of methane. Anaerobic. Saprophytes. The type species is Methanococcus mazei Barker. 1. Methanococcus niazei Barker, 1936. (Pseudosarcina, Maze, Compt. rend. Soc. Biol., Paris, 78, 1915, 398; Barker, Arch. f. Mikrobiol., 7, 1936, 430.) ma'ze.i. M.L. gen .noun mazei of Maze; named for P. Maze, the French bacteriolo- gist who first gave a clearh^ recognizable description of this tj'pe of methane or- ganism. Small, spherical cells occurring singh", in large, irregular masses or in regular cysts of various sizes and forms. Non-motile. Stains readily with erythrosine. Gram-variable. Grows in a mineral medium containing acetate, fermenting the acetate vigorously. Ferments acetate and butyrate with the production of methane and carbon dioxide. Ethanol and butanol not attacked. Ammonia nitrogen utilized, but not ni- trate nitrogen. Yeast extract is not bene- ficial. Anaerobic. Optimum temperature, between 30° and 37° C. Source: Isolated from garden soil, sewage sludge, black mud containing hydrogen sulfide and from the feces of herbivorous animals. Habitat: One of the most active methane- producing organisms found in nature. 2. Methanococcu.s vannielii Stadtman and Barker, 1951. (Jour. Bact., 62, 1951, 269.) van.niel'i.i. M.L. gen. noun vannielii of van Niel; named for C. B. van Niel, the American bacteriologist who developed the carbon dioxide reduction theory of methane formation. Cocci, often slightly ellipsoidal, which vary from 0.5 to 4.0 microns in diameter and which frequently occur in pairs. Motile. Cells disintegrate on drying. Stain readily with erj^throsine. Gram stain not recorded. Agar deep colonies: 0.5 to 1.0 mm in di- ameter, lenticular and light brown with edges regular or slightly lobate. Acetate, propionate, butyrate, succinate, glucose, ethanol and methanol are not at- tacked when incorporated in a mineral-bi- carbonate medium of pH 8.0 at a concentra- tion of 0.5 per cent; under similar conditions, formate supports good growth. Sodium formate in concentrations of 1.5 per cent permits maximum growth; at the 2 and 3 per cent levels, growth is slower, and in 5 per cent sodium formate there is no growth. Formate, the only organic compound known to support growth, is fermented to Prepared by Prof. H. A. Barker, University of California, Berkeley, California, October, 1955.
