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Morphology and ultrastructure of Mycoplasma pneumoniae spherules
Abstract:
During growth in fluid medium, most strains of Mycoplasma pneumoniae produce free-floating granules which become larger with time. We have called these granules "spherules." This study describes the morphological and ultrastructural features of M. pneumoniae strain AP-164 spherules, both free and in association with HeLa cells in cell culture. In thin section, spherules were composed of lobulated cells, connected together by membranes, and ring-shaped cells. The two-dimensional morphology observed varied according to the plane of section and to the age of the culture. In HeLa cell cultures, mycoplasmata were found attached to plasma membranes of cells; in sections, individual mycoplasmata were often aligned in radial apposition to the membranes. Mycoplasmata were not found intracellularly. The three-dimensional morphology of spherules was examined by the critical point method and by scanning electron microscopy. Both methods revealed lobulated forms, ring-shaped forms, and star-shaped forms. Treatment of the spherules with crude porcine pancreatic lipase effectively released large numbers of free organisms. Phosphotungstic acid preparations of these uncentrifuged forms revealed a morphology in agreement with the other methods used. Lobulated ring forms with "beaded" filaments were prominent. In respect to morphology, M. pneumoniae under our conditions resembles that of the type species M. mycoides.
Insights
Mycoplasma pneumoniae forms unique "spherules" in liquid culture, which are complex structures of connected cells. These spherules, when treated with lipase, release individual Mycoplasma pneumoniae organisms.
Area of Science:
- Microbiology
- Cell Biology
Background:
- Mycoplasma pneumoniae is a significant human pathogen.
- Typical M. pneumoniae morphology in fluid culture is not well-characterized.
- The existence of complex M. pneumoniae structures like spherules requires further investigation.
Purpose of the Study:
- To describe the morphological and ultrastructural features of M. pneumoniae strain AP-164 spherules.
- To examine spherule morphology in free-floating cultures and in association with host cells.
- To investigate the relationship between spherules and individual M. pneumoniae organisms.
Main Methods:
- Thin section electron microscopy for 2D morphology.
- Critical point drying and scanning electron microscopy for 3D morphology.
- Lipase treatment to release organisms and phosphotungstic acid staining for ultrastructural analysis.
Main Results:
- Spherules are composed of lobulated, ring-shaped, and star-shaped cellular forms connected by membranes.
- M. pneumoniae was observed attached to the plasma membranes of HeLa cells, but not intracellularly.
- Lipase treatment effectively released free M. pneumoniae organisms from spherules, revealing lobulated ring forms with beaded filaments.
Conclusions:
- M. pneumoniae strain AP-164 produces complex, multi-cellular spherules in fluid culture.
- Spherule morphology is diverse and changes with culture age and preparation method.
- The observed morphology of M. pneumoniae under these conditions is similar to Mycoplasma mycoides.