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Fine structure of Cryptococcus neoformans grown in vivo as observed by freeze-etching
Abstract:
Cryptococcus neoformans grown in the parasitic state was observed by the freeze-etching technique and was compared with that grown on culture media. Unlike other yeasts, this organism grown in vivo is very often devoid of the "ordinary" invaginations. The membrane of the cell grown in vivo was almost free from concavity and convexity except for many round depressions which represent the surface view of paramural bodies. Some of the paramural bodies were found to be multivesicular systems. Most were spherical invaginations containing a single vesicle or its ghost remaining after secretion of the vesicles. In clear contrast to the cell grown in vitro, the in vivo cell contained a great number of vesicles in the cytoplasm. These seemed to show high-secretion activity in C. neoformans grown in the parasitic state. On transfer from in vitro to in vivo, this organism enlarged the cell wall, capsule, and cell body. The appearance of a large vacuole, accumulation of storage organelles, and the existence of rodlike structures, seemingly lipid deposits, were also noted in the cytoplasm of the cell grown in vivo. the meaning of these results as well as the mode of capsular production are discussed.
Insights
Cryptococcus neoformans exhibits distinct cellular structures when grown in vivo versus in vitro. The parasitic form shows increased vesicle activity and cell enlargement, suggesting high secretion during infection.
Area of Science:
- Microbiology
- Cell Biology
- Mycology
Background:
- Cryptococcus neoformans is a significant human pathogen.
- Understanding its parasitic form is crucial for developing effective treatments.
- Previous studies have focused on in vitro characteristics, with limited in vivo ultrastructural data.
Purpose of the Study:
- To investigate the ultrastructural differences of Cryptococcus neoformans in its parasitic (in vivo) state compared to its culture (in vitro) state.
- To elucidate the cellular mechanisms underlying C. neoformans' adaptation and survival within a host.
Main Methods:
- Freeze-etching electron microscopy was employed to visualize the cell surface and internal structures.
- Comparative analysis was performed between yeast cells grown in vivo (parasitic state) and in vitro (culture media).
Main Results:
- In vivo cells, unlike in vitro cells, typically lacked ordinary invaginations, showing a smoother cell membrane with depressions indicating paramural bodies.
- Paramural bodies were identified as multivesicular systems or spherical invaginations containing vesicles, suggesting active secretion.
- In vivo cells displayed significantly more cytoplasmic vesicles, enlarged cell walls, capsules, and cell bodies, along with large vacuoles and lipid deposits.
Conclusions:
- Cryptococcus neoformans demonstrates high secretory activity in its parasitic state, likely contributing to virulence.
- In vivo adaptation involves significant cellular changes, including cell wall and capsule enlargement, and the formation of storage organelles.
- These findings provide insights into the pathogenesis of cryptococcosis and potential targets for antifungal therapies.