Electrophoretic Characterization of Ribosomal Proteins from Methanogenic Bacteria

Ribosomes from the following strains of methanogenic bacteria were isolated and their protein patterns analysed by twodimensional polyacrylamide gel electrophoresis: Methano-sarcina (Ms.) barkeri (DSM 800); Ms. barkeri (morphotype II) (DSM 1232); Methanococcus (Mc.) vannielii (DSM 1224); Methanobacterium (Mb.) thermoautotrophicum (DSM 1053); Mb. arbophilicum (DSM 1125); Mb. formicicum and Mb. strain M. o. H. Ribosomes from Ms. barkeri were analysed in more detail. They possess an apparent sedimentation constant of 70S and dissociate at 1 mM Mg⁺⁺ into 30S and 50S subunits. Electropherograms of 30 S subunits purified twice on sucrose gradients exhibit at least 27 protein spots, those for 50S subunits at least 33. The individuality of these spots has not yet rigorously been determined. The electrophoretic pattern of the two strains of Ms. barkeri investigated differ with respect to a considerable number of proteins, which indicates a high degree of diversity even within one morphologically similar group.

The number of ribosomal proteins, as judged from the 70S electropherograms from other methanogens studied, lies in the typical “procaryotic” range, between 50 and 55. Striking, however, is the large number of acidic proteins in all strains, Their content is highest in Mb. arbophilicum, in which almost 2/3 of the proteins are acidic, and lowest in Mc. vannielii, of which about 1/3 of the total number of ribosomal proteins migrate to the anode. As ribosomes from extreme halophiles consist almost exclusively of acidic proteins, this unusual property is consistent with the comparatively high degree of 16 s RNA sequence homologies between halobacteria and one specific group (group I) of the methanogens (Magrum et al, 1978). Those species from group I investigated (Mb. arbophilicum; Mb. formicicum; Mb. strain M.o.H) also exhibit a qualitative resemblance in their ribosomal protein pattern; the patterns from Mb. formicicum and Mb. strain M.o.H are very similar. The practical value of ribosomal protein determination for the rapid identification or comparison of unclassified isolates is discussed.