Habitat: Found in soil and in naturally retting plant materials. Nolc: Species incerlae sedis. The relation- ships of Melhanohaclerium soehngenii Barker and Methanobacterium omelianskii Barker to other species of bacteria are not entirely- clear. M. soehngenii, a non-motile, non- sporeforming, Gram-negative species, has tentatively been placed in the family Spiril- laceae. While M. omelianskii was described for some time as being non-motile and non- sporeforming, it was later found to be defi- nitely motile at times, to form spores and to be Gram- variable. As an anaerobe, it should be placed in the genus Clostridium. If, however, it were placed in the genus Clostridium, it could not bear the specific epithet omelianskii, as this epithet is pre- empted by the cellulose-fermenting Clos- tridium omelianskii (Henneberg, emend. Clausen) Spraj', a different organism. While awaiting a better determination of the rela- tionships of Methanobacterium omelianskii, this organism has been placed here. 1. Methanobacterium omelianskii Barker, 1936. (Bacille de la decomposition methanique de I'alcohol ethylique, Omelian- sky, Ann. Inst. Past., 30, 1916, 56; Barker, Arch. f. Mikrobiol., 7, 1936, 436; also see Antonie van Leeuwenhoek, 6, 1940, 201; and Jour. Biol. Chem., 137, 1941, 153.) o.me.li.an'ski.i. M.L. gen. noun omelian- skii of Omeliansky; named for Prof. W. Omeliansky, the Russian bacteriologist who was the first to observe this organism. Rods, 0.6 to 0.7 by 1.5 to 10.0 microns, usually 3.0 to 6.0 microns in length. Origi- nally described as non-sporeforming (Omel- iansky, op. cit., 1916, 60; Barker, op. cit.. 1936, 437), this organism was later found to form spores of low heat resistance which are spherical and terminal and which swell the cells (Barker, op. cit., 1940, 207). Ini- tiall}^ reported as non-motile (Barker, op. cit., 1936, 437) but later observed to be oc- casionally and feebly motile, the type of flagellation not determined (Barker, op. cit., 1940, 207). At first described as Gram- negative (Barker, op. cit., 1936, 437), the cells were later reported to be Gram-var- iable (Barker, op. cit., 1940, 208). Primary alcohols, including ethanol, pro- panol, n-butanol and n-amyl alcohol, are oxidized to the corresponding fatty acids. Secondary alcohols, including isopropanol and sec-butanol, are oxidized to the corre- sponding ketones. Hj-drogen is oxidized. Ethanol is utilized the best of all organic compounds. Carbon dioxide is utilized and converted to methane. Growth and alcohol oxidation are directly proportional to the carbon diox- ide supply, at low concentrations. Fatty and hydroxy acids, glucose and other polyhydroxy alcohols and amino acids are not attacked. Ammonia is utilized as a nitrogen source. Nitrate, sulfate and oxygen cannot be used as oxidizing agents. Obligate anaerobe. Optimum temperature, between 37° and 40° C. Maximum, between 46° and 48° C. Growth limits, pH 6.5 and 8.1. Source: Isolated from soil, fresh-water and marine muds, rabbit feces and sewage. Pure cultures were isolated from fresh-water and marine muds (Barker, op. cit., 1940, 201). Habitat: Found wherever organic matter is decomposing in an anaerobic, approxi- mately neutral environment.
