In Vivo and In Vitro Interactions between Exopolysaccharides from Bacillus thuringensis HD270 and Vip3Aa11 Protein

Area of Science:

• Agricultural Entomology
• Molecular Biology
• Biochemistry

Background:

• Bacillus thuringiensis (Bt) Vip3Aa11 protein is toxic to fall armyworm (Spodoptera frugiperda).
• Bt HD270 extracellular polysaccharide (EPS) enhances Vip3Aa11 protoxin toxicity by improving brush border membrane vesicle (BBMV) attachment.
• The in vivo interaction of EPS-HD270 with Vip3Aa11 protoxin and its effect on activated Vip3Aa11 toxin remain unclear.

Purpose of the Study:

• To investigate the interaction between EPS-HD270 and Vip3Aa11 protoxin in vivo.
• To determine the effect of EPS-HD270 on the toxicity of activated Vip3Aa11 toxin against Spodoptera frugiperda.

Main Methods:

• Interaction analysis between mannose (a component of EPS-HD270) and Vip3Aa11 protoxin using dissociation constant (Kd).
• Laser confocal microscopy to observe co-localization of EPS-HD270 and Vip3Aa11 protoxin in insect midguts.
• Binding capacity assays to compare protoxin and activated toxin binding to EPS-HD270 and BBMVs.

Main Results:

• Mannose in EPS-HD270 interacts with Vip3Aa11 protoxin (Kd = 16.75 ± 0.95 mmol/L).
• EPS-HD270 and Vip3Aa11 protoxin co-localized in the midgut, increasing BBMV damage.
• EPS-HD270 did not synergize activated Vip3Aa11 toxin; activated toxin showed reduced binding to EPS-HD270 and BBMVs.

Conclusions:

• EPS-HD270 enhances Vip3Aa11 protoxin toxicity through interaction with mannose and BBMVs in the fall armyworm midgut.
• The synergistic effect is specific to the protoxin form; activation of Vip3Aa11 reduces EPS-HD270's enhancing capability.
• Findings elucidate the mechanism of synergistic insecticidal action between EPS and Vip3Aa11 protein.