Electron Microscope Observations on Intact Cells, Protoplasts, and the Cytoplasmic Membrane of Bacillus stearothermophilus

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Abram, Dinah (Purdue University, Lafayette, Ind.). Electron microscope observations on intact cells, protoplasts, and the cytoplasmic membrane of Bacillus stearothermophilus. J. Bacteriol. 89:855–873. 1965.—Negatively stained preparations of protoplasts and fragments of cytoplasmic membranes from cells of Bacillus stearothermophilus ruptured by treatment with sonic oscillation, partial lysis with lysozyme, autolysis, or phage infection were examined electron microscopically. Specimens of intact cells also were examined by the same technique. The following structural details were revealed. Intact or nearly intact, partially swollen, elongated protoplasts and their ghosts have a characteristic differentiated surface texture and can easily be distinguished from the cell wall. Infoldings of the cytoplasmic membrane can be observed in these protoplasts, to which flagella are attached; the latter originate via hooks from “basal structures” that are in close association with the cytoplasmic membrane or part of it. Abundant intracytoplasmic membranous elements, which appear to be tubular or vesicular, can be seen in whole cells of three of the strains studied. The fine structure of the cytoplasmic membrane and probably that of its intracytoplasmic infoldings was observed on flattened and folded membrane fragments, one layer thick. Structural units, roughly spherical, 65 to 85 A in diameter, were present on one side of the cytoplasmic membrane, facing the cytoplasm. They were attached loosely to the membrane by fine stalks, 40 to 60 A long, and were easily detached, probably leaving the stalks behind them on the membrane. While the greater stability of membranes from thermophiles made this study of the fine structure possible, the structural units described were demonstrated also on cytoplasmic membranes from mesophiles.

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