Abstract

SUMMARY: The mate-killer (mu) particles in the cytoplasm of Paramecium aurelia, stock 540, variety (syngen) I, were studied by: Feulgen-staining; phase-contrast microscopy; fluorescence under ultraviolet irradiation after staining with acridine orange; electron microscopy (including the ‘silver-Feulgen’ technique). The appearance of the particles following treatment with DNAase and RNAase was observed. It was found that the mu particles were capsulated rod-shaped structures, 2-10μ long and about 0·3 μ in diameter (excluding the capsule); they appeared to reproduce by transverse fission without formation of cross-walls. There was an external double membrane and the internal material consisted largely of DNA, which was not limited to particular zones but spread throughout the interior of the particle. RNA was also present. The relationships of the particles to other micro-organisms is discussed, and it is concluded that they do not differ from bacteria in any important respect.

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