Electron microscope study of the structure of Holospora caryophila

The ultrastructure of the symbiont Holospora caryophila found in the macronucleus of Paramecium biaurelia has been studied in the electron microscope following preparation by thin sections, negative staining and shadow-casting techniques. Holospora were identified by their characteristic morphology of slender elongated cells when seen in whole mounts in negative stain or contrasted with shadowing. The long forms were seen to possess a helical configuration, also an asymmetrical shape.Thin sections of Holospora revealed the cell envelope structure consistent with a Gram-negative organism. A complex network of internal membranes, together with a relatively electron transparent region at one end of the cytoplasm, was frequently observed.