Electron microscopy of frozen-hydrated bacteria.

Amorphous, unstained, frozen-hydrated sections of bacteria provide a faithful high-resolution image of procaryotic cells. Conventional preparation artifacts due to fixation, staining, and dehydration are nonexistent. Freezing damage is avoided by using glucose as a cryoprotectant. Cutting damage on frozen material is severe, but sectioning artifacts, being always related to the cutting direction, can be systematically recognized and thus taken into consideration. Geometry and density distribution of the bacterial envelope can be resolved to about 3 nm. The following main features have been observed. In Escherichia coli the inner and outer membranes have an approximately uniform density profile. The distance between the two membranes is constant, ca. 33 nm. In Staphylococcus aureus the cell wall is ca. 40 nm wide. It is bordered on the cytoplasmic side by an asymmetric 5.5-nm-wide bilayer. The bacterial nucleoid, clearly visible with conventional preparation methods, appears in exponentially growing bacteria as an ill-defined central region with approximately the same density as the rest of the cytoplasm. It becomes more clearly visible when bacteria are in the stationary phase, plasmolysed, fixed, or stained. We confirm that "mesosomes," hitherto quite often considered to be essential organelles in all procaryotes, are artifacts. They appear in large numbers during osmium fixation.

The fine structure of monoclonal Hodgkin cells cultured in diffusion chambers.

Pleural effusion cells from two patients with stage IV Hodgkin's disease have been cultured continuously in diffusion chambers in mice and studied by electron microscopy after a culture period exceeding 100 days. Cell identity and monoclonal growth in culture has been documented by marker chromosomes (Hossfeld and Schmidt, 1978). These cultured cells grow in close connection, projecting pseudopode-like processes into the intercellular spaces. Most nuclei are lobulated. They always are of low electron density with a norrow rim of condensed chromatin confined to the nuclear membrane. One large prominent nucleolus and up to four smaller nucleoli are found. Nuclear pockets in case 1 and deep cytoplasmic invaginations into the nuclear area in both cases frequently occur. In the cytoplasm, besides microtubuli and fibrils, the Golgi apparatus and mitochondria are the predominant organelles. Most mitochondria appear to be dilated containing fragmented cristae. Free ribosomes and polysomal aggregates are randomly distributed. The ratio nucleoplasm:cytoplasm, on the average, is 0.7 in both cases and the cell diameters lie distinctly above those of lymphocytes. At the electron microscope level these cultured monoclonal cells of Hodgkin's disease are not distinguishable from those described in genuine Hodgkin material. Their probable origin and apparent relation to true histiocytic lymphoma cells will be discussed.

Studies on the fine structure of corynebacterium diphtheriae-granules.

The seemingly homogeneous metachromatic and electron-scattering granules of Corynebacterium diphtheriae have two structural components as revealed under conditions of low beam load and by use of ribonuclease. They contain high percentages of P and Ca. Findings point to participation of ribosomes and intracytoplasmic membranes in the formation of the granules.