Ref ID : 7665
Maria Lasman and Noemi Feinstein; Ultrastructural Changes during Encystment of Acanthamoeba rhysodes. Protistologica XXII(3):257-264, 1986
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The ultrastructural of the trophozoite of Acanthamoeba rhysodes is, in general, similar to that of other species of Acanthamoeba. It differs from them in the following features: Golgi bodies are small, scarce and poorly developed; large polyvesicular bodies, bound by a double membrane, are abundant; the cytoplasmic matrix is rich in microfilaments and microtubules. The osmotic and chemical requirements of A. rhysodes in liquid axenic cultures differ from those of other closely related species, grown in identical conditions. Encystment can be induced only by the use of Band's replacement medium. The most prominent ultrastructural change, occurring at the early phase of encystment, is the appearance of electron-dense (black) granules in the cell periphery in close contact with the plasma membrane. Other changes during encystment include: increase in fibrilar material, arranged in large bundles which penetrate deep into the cytoplasm; appearance of numerous autophagosomes, containing vesicles, granules and myelinated bodies. Upon formation of the outer cyst wall, vesicles enclosed by plasma membrane, containing cytoplasmic material, are found in the space between the cyst wall and cell membrane, some of which are embedded in the wall material. The mature cyst, that lacks the peripheral black granules, consists of a thin granular endocyst and a thicker fibrilar exocyst, separated by a almost transparent space. The endocyst and the exocyst are closely apposed to each other in the area where the two walls meet, thus forming an operculum-like structure. The results are discussed with regards to classification of A. rhysodes.