The cell envelopes of three species of Methanococcus with growth optima within the mesophilic, thermophilic, and extremely thermophilic temperature range were investigated. Methanococcus vannielii, Methanococcus thermolithotrophicus, and Methanococcus jannaschii possess surface layers of hexagonally arranged protein subunits. Glycosylated proteins were not found. The main surface layer proteins of the three species have different molecular weights, which can be taken as additional taxonomic markers. The amino acid composition of the main surface layer proteins shows no significant differences. The acidic amino acids exceed the basic amino acids and the nonpolar amino acids are predominant.
Glycogen was isolated from Methanolobus tindarius and 4 species of Methanococcus. It was identified by the iodine reaction, determination of glucose, maltose and isomaltose in acid hydrolysates and partial acid hydrolysates, respectively, determination of erythritol and glycerol after periodate oxidation and treatment with amyloglucosidase. Glycogen particles in the cells are distributed throughout the cytoplasm. Ml. tindarius can use elemental nitrogen and cysteine as nitrogen source. The glycogen and polyphosphate content of cells of Ml. tindarius increased under nitrogen limitation. During incubation without external energy source, glycogen decreased and methane formation was correlated to the glycogen content of the cells.
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