Freeze‐Fracture Study of Blastocystis hominis¹

Abstract

The ultrastructure of Blastocystis hominis was investigated by the freeze-fracture method. Freeze-fracture replicas of the membranes of B. hominis and its organelles were studied with special regard to the density and distribution of the intramembranous particles (IMP's). On all membrane replicas, the concentration of IMP's on the protoplasmic face (P face) invariably was greater than on the exoplasmic face (E face). On the P face, IMP's were heterogeneously distributed in dense aggregates, alternating with particle-free, smooth surface areas. Occasionally, small depressions and protrusions were observed in these areas. On the membrane of the central vacuole, invaginations into the vacuole were frequently observed within the smooth surface regions. Since most of the granules in the central vacuoles had no IMP's, it seems likely that the intervacuolar granules were formed from these invaginations of the vacuole membrane. The width of the intermembrane space between the inner and outer membranes of the nuclear envelope was uneven, with regions of relative narrowness interspersed with regions of expansion. Nuclear pores were localized within the narrow portions of this space. A nucleus, apparently in the process of dividing, was observed enclosed within an intact outer membrane. Division of the outer membrane would then result in the formation of two discrete nuclei.

Freeze‐Fracture and Cytoehemical Studies on the in Vitro Cyst Form of Reptilian Blastocystis pythoni

“…The size of these depressions and protrusions was 113.3 × 9.7 μm (n = 38) on the P face and 91.8 μ 8.8 μm (n = 36) on the E face. These measurements were similar to those reported previously for B. hominis (Yoshikawa and Hayakawa 1996; Yoshikawa, Yamada, and Yoshida 1988b). In freeze‐fracture images, the cyst form could be clearly distinguished from non‐cyst cells by its characteristic thick wall (Fig.…”

“…The size and morphology of particle‐rich small depressions and smooth small protrusions observed on the P face and E face of non‐cyst cells, respectively, were very similar to endocytic sites reported in B. hominis (Yoshikawa and Hayakawa 1996; Yoshikawa, Yamada, and Yoshida 1988b). Therefore, these structures in non‐cyst cell of B. pythoni are probably endocytic sites.…”

“…1). Since electron microscopy revealed many transition forms between vacuolar and granular forms (described by Yoshikawa, Kuwayama, and Enose 1995; Yoshikawa, Satoh, and Enose 1995; Yoshikawa, Yamada, and Yoshida 1988b), they are described collectively here as non‐cyst cells.…”

Blastocystis hominis revisited

“…Lipid droplets also were noted in the cytoplasm (49). Granules that appear similar to those in the central vacuole have been found in small vacuoles and vesicles in the cytoplasm of granular cells (49,217).…”

“…Multiple nuclei are present in some cultured cells from most isolates, with up to four reported to be common (49,129,223). The nuclei are approximately 1 m in diameter and are surrounded by a nuclear envelope with nuclear pores (176,215,217). A crescentic band of electron-opaque material, characteristic of all forms of B. hominis (23,49,129,192,215,227,228,231,234), is noted in electron micrographs of the nuclei, and occasionally an additional spot of electron-opaque material is seen (23).…”