Cytoskeletal components can turn wall-less spherical bacteria into kinking helices

Area of Science:

• Microbiology
• Cell Biology
• Bacterial Cytoskeleton

Background:

• Bacterial cell shape is primarily determined by the peptidoglycan cell wall and MreB protein filaments.
• Mycoplasma species, lacking a cell wall, are typically spherical or pleomorphic.
• Spiroplasma, also wall-less, exhibit helical shapes and unique motility, attributed to MreB isoforms and a fibril protein.

Purpose of the Study:

• To investigate the role of Spiroplasma MreB isoforms and fibril protein in determining bacterial cell shape.
• To determine if Spiroplasma components can confer helical morphology and motility to Mycoplasma.

Main Methods:

• Heterologous expression of Spiroplasma MreB proteins and fibril protein in Mycoplasma capricolum.
• Cryoelectron microscopy to visualize MreB filament association with the plasma membrane.
• Observation of cell shape, helicity, and kinking ability.

Main Results:

• Heterologous expression of Spiroplasma MreB and fibril proteins induced helical shape and kinking in Mycoplasma capricolum.
• Spiroplasma MreB isoform 5 (MreB5) was sufficient to confer helicity and kink propagation.
• Cryoelectron microscopy revealed MreB filaments associated with the plasma membrane, suggesting a role in membrane curvature.
• Motility in culture broth was not efficiently achieved, indicating other Spiroplasma factors are necessary.

Conclusions:

• Spiroplasma MreB proteins, particularly MreB5, and the fibril protein are key determinants of helical cell shape and kinking.
• MreB filaments directly influence bacterial membrane curvature.
• While Spiroplasma components can induce shape changes, additional factors are required for efficient motility.