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Intracellular structures of Mycoplasma pneumoniae revealed after membrane removal
Abstract:
Mycoplasma pneumoniae was grown on Formvar- and carbon-coated electron microscope grids and treated with the nonionic detergent Triton X-100 to gently remove the membrane and cytoplasm. The detergent mixture was composed of 0.5% Triton X-100 in SSR-2 broth base. After this treatment, the grids were rinsed in a mixture of 0.1 M KCl, 5 mM MgCl2, and 6 mM potassium phosphate buffer (pH 7.05) and negatively stained with uranyl acetate. The Triton X-100-resistant remains of M. pneumoniae after gentle removal of the membrane and cytoplasm consisted of fibrous structures oriented similarly to the undisrupted cells. The thin fibers displayed a negative staining quality and diameter analogous to that of rabbit muscle F-actin. The fibrous moieties ended in rodlike condensations which appeared striated in negatively stained and shadowed preparations. These striations were regular, and the majority of rod structures had lengths of 220 to 300 nm and widths of 50 to 80 nm. Specific antibody to rabbit muscle actin, produced in guinea pigs, was used in indirect immunofluorescence of the M. pneumoniae colonies. Fluorescence was detected, with concentrations at the colony center and at the tips of filamentous cells.
Insights
This study reveals that Mycoplasma pneumoniae contains fibrous structures resembling actin. These structures, similar to rabbit muscle F-actin, are concentrated in the cell center and tips, suggesting a potential role in cell shape and motility.
Area of Science:
- Microbiology
- Cell Biology
- Biochemistry
Background:
- Mycoplasma pneumoniae is a bacterium lacking a cell wall, making its structural components of significant interest.
- Understanding the cytoskeleton and structural proteins of M. pneumoniae is crucial for elucidating its pathogenicity and host interactions.
Purpose of the Study:
- To investigate the Triton X-100-resistant structural components of Mycoplasma pneumoniae.
- To determine if M. pneumoniae possesses actin-like proteins and their cellular localization.
Main Methods:
- Mycoplasma pneumoniae cells were treated with Triton X-100 to remove membrane and cytoplasm.
- Remaining structures were analyzed using negative staining electron microscopy.
- Indirect immunofluorescence with anti-actin antibodies was employed to detect actin-like proteins.
Main Results:
- Triton X-100 treatment revealed fibrous structures in M. pneumoniae, similar in diameter to rabbit muscle F-actin.
- These fibers terminated in striated, rod-like condensations (220-300 nm length, 50-80 nm width).
- Immunofluorescence confirmed the presence of actin-like material concentrated at the colony center and tips of filamentous cells.
Conclusions:
- Mycoplasma pneumoniae possesses fibrous structures analogous to actin.
- These actin-like filaments are localized within the cell, potentially influencing cell morphology and behavior.
- The findings suggest a conserved role for actin-like proteins in bacterial structure and function.