[Comparative electron microscopic study of Bacillus thuringiensis cells grown in a chemostat]

Area of Science:

• Microbiology
• Bacterial Genetics
• Cell Biology

Background:

• Bacillus thuringiensis subsp. gall. 69-6 dissociates into R- and S-variants in chemostat culture.
• Understanding variant-specific traits is crucial for microbial ecology and biotechnology.

Purpose of the Study:

• To investigate the differences in sporogenesis, toxin production, and bacteriophage resistance between R- and S-variants of Bacillus thuringiensis subsp. gall. 69-6.
• To elucidate the structural basis of bacteriophage resistance in S-variant cells.

Main Methods:

• Chemostat culture of Bacillus thuringiensis subsp. gall. 69-6.
• Electron microscopy for cell wall structural analysis.
• Negative contrast microscopy to study T-layer organization.

Main Results:

• Both R- and S-variants exhibited similar sporogenesis and toxin production after 24 hours, despite earlier initiation in S-variants.
• S-variant cells demonstrated significant resistance to bacteriophage infection.
• Electron microscopy revealed a thin, crumbly peptidoglycan layer in S-variants and a regularly structured T-layer in R-variants, facilitating phage adsorption and lysis.

Conclusions:

• The S-variant's cell wall structure, specifically the T-layer's protein subunit redistribution, prevents bacteriophage adsorption, conferring resistance.
• Phagoresistance is a key advantage for S-variant survival in environments with bacteriophages.
• Structural differences in cell wall organization dictate variant-specific interactions with bacteriophages.