Bacillus thuringiensis subsp. israelensis and its dipteran-specific toxins

Area of Science:

• Microbiology
• Entomology
• Biochemistry

Background:

• Bacillus thuringiensis subsp. israelensis (Bti) is a widely used biological control agent.
• It targets larvae of various mosquito and black fly species globally.
• Its efficacy stems from specific insecticidal crystal proteins (δ-endotoxins).

Purpose of the Study:

• To detail the composition and function of Bti's larvicidal toxins.
• To explain the synergistic interactions between different toxin types.
• To assess the long-term viability of Bti as a pest control agent.

Main Methods:

• Analysis of polypeptide composition and encoding genes (cry and cyt) of Bti.
• Characterization of the parasporal crystalline body structure.
• Toxicological studies on mosquito larvae (Aedes, Culex, Anopheles).

Main Results:

• Bti produces major (134, 128, 72, 27 kDa) and minor (78, 29 kDa) polypeptides encoded by cry and cyt genes on the pBtoxis plasmid.
• Cry toxins form channels, while Cyt toxins act as membrane perforators.
• Cyt toxins exhibit synergy with Cry toxins, preventing resistance development.

Conclusions:

• Bti's δ-endotoxin complex exhibits high specificity and toxicity against target larvae.
• Synergistic interactions between Cry and Cyt toxins are crucial for Bti's efficacy and resistance management.
• The lack of field resistance confirms Bti's sustained potential as a biocontrol agent.