Bacillus sphaericus asporogenous mutants: morphology, protein pattern and larvicidal activity

Area of Science:

• Microbiology
• Molecular Biology
• Insect Toxicology

Background:

• Bacillus sphaericus produces insecticidal toxins during sporulation.
• Understanding the genetic and molecular basis of toxin production is crucial for developing effective biocontrol agents.

Purpose of the Study:

• To investigate the relationship between Bacillus sphaericus sporulation stages and the production of insecticidal crystal proteins.
• To correlate the presence and stage of crystal formation with toxicity against Culex pipiens mosquito larvae.

Main Methods:

• Isolation and characterization of asporogenous mutants of Bacillus sphaericus.
• Analysis of crystalline inclusions using microscopy and protein electrophoresis.
• Toxicity assays against Culex pipiens larvae.
• Western blot analysis using antisera against crystal proteins.

Main Results:

• Early-sporulation blocked mutants (e.g., 2297 Aspo30A, 2297 Aspo34) lacked crystalline inclusions and showed poor toxicity to mosquito larvae.
• Late-sporulation blocked mutants (e.g., 2297 Aspo115, 2297 Aspo24, 1593-4 Aspo12) synthesized crystal-like inclusions and exhibited high toxicity.
• Electrophoretic and Western blot analyses confirmed the absence of crystal proteins in early mutants and their presence in later mutants.

Conclusions:

• The synthesis of toxic crystal proteins in Bacillus sphaericus is dependent on progression through specific stages of the sporulation process.
• The presence of crystalline inclusions is directly correlated with the insecticidal activity against mosquito larvae.