Ultrastructural investigation of 12 Methanosarcinae and related species grown on methanol for occurrence of polyphosphatelike inclusions

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Abstract
A comparative investigation by electron microscopy of 12 strains and species belonging to the Methanosarcinaceae family of methanogenic bacteria revealed the existence of polyphosphatelike bodies during growth on methanol in an optimized medium. The Methanosarcina barkeri strains Fusaro, 227, and Wiesmoor, and M. vacuolata were found to contain smoothly marginated, polyphosphatelike inclusions. They were identified by a positive Neisser stain, by the absence of a boundary membrane, and by X-ray microanalysis in situ. They had a diameter of 0.15–0.25 µm and contained the elements Ca, P, and Fe, and sometimes Mg, S, and Cl. In addition to the polyphosphatelike bodies, coarse-looking electron-dense "granula" were observed in the cytoplasm of most of the strains. They had an average diameter of 30 nm and the same elemental composition as the polyphosphatelike bodies. As demonstrated for M. barkeri Fusaro, the "granula" were also present in cells grown in acetate and H2–CO2.