Cross-membranes orchestrate compartmentalization and morphogenesis in Streptomyces

Area of Science:

• Microbiology
• Cell Biology
• Bacterial Development

Background:

• Bacteria exhibit complex social behaviors and multicellular organization.
• Filamentous streptomycetes demonstrate multicellularity through syncytial mycelial growth with distinct hyphal compartments.
• The existence of viable cell division mutants suggests alternative compartmentalization mechanisms beyond cross-walls.

Purpose of the Study:

• To investigate the role of internal membrane structures in compartmentalizing multinucleoid bacterial mycelia.
• To elucidate the function of these membranes in bacterial development and organization.
• To identify novel mechanisms controlling bacterial multicellularity.

Main Methods:

• Cryo-correlative light and electron microscopy for visualizing membrane structures.
• Cryo-electron tomography to determine high-resolution ultrastructure.
• Fluorescence Recovery After Photobleaching (FRAP) experiments to assess membrane permeability.

Main Results:

• Complex internal membranes were visualized between the cell wall and cytoplasmic membrane.
• Large, protein-impermeable cross-membrane structures were identified, compartmentalizing the multinucleoid mycelium.
• Areas with these membrane structures were nucleoid-restricted, suggesting a role in nucleoid protection.

Conclusions:

• Internal membrane assemblies represent a novel form of compartmentalization in multicellular bacteria.
• These membrane structures play a crucial role in organizing the multinucleoid mycelium.
• Membrane structures may protect bacterial nucleoids from external cellular events.