The structure of Mycoplasma pneumoniae as determined by the freeze-substitution technique.

The ultrastructure of Mycoplasma pneumoniae FH was examined by a mild fixation method, the freeze-substitution technique, for thin-section transmission electron microscopy and the following new findings were obtained. In the cytoplasm, no nuclear region could be clearly identified. The cytoplasm was filled with many ribosome-like particles, fine fibers and electron-dense particles. The electron-dense particles appeared to be similar to the particles found in the nucleoid region of Pseudomonas aeruginosa and might therefore possibly be a kind of DNA binding protein. The cell surface was completely enveloped with a thin opaque layer. The presence of this surface layer prevented any direct contact of the cell surface with that of the two M. pneumoniae cells.