Bacillus thuringiensis HD-73 Spores Have Surface-Localized Cry1Ac Toxin: Physiological and Pathogenic Consequences

Area of Science:

• Microbiology
• Molecular Biology
• Insect Toxicology

Background:

• Bacillus thuringiensis produces Cry toxins for insecticidal activity.
• Cry toxins are crucial for pathogenicity in insect larvae.
• Spore surface properties influence B. thuringiensis interactions with hosts.

Purpose of the Study:

• To investigate the role of Cry toxins on Bacillus thuringiensis spore surfaces.
• To determine the binding of Cry toxins to insect gut receptors.
• To understand the implications of surface-localized toxins for spore germination and pathogenesis.

Main Methods:

• Immunofluorescence labeling of Cry toxins on spores.
• Germination assays under alkaline conditions.
• Binding assays with insect gut brush border membrane vesicles.
• Protease treatment to expose surface toxins.

Main Results:

• Cry-positive (Cry+) spores bound antibodies specific to activated Cry 1Ac toxin.
• Cry+ spores germinated in alkaline conditions, unlike Cry-negative (Cry-) spores.
• Permeabilized or exosporia-removed Cry+ spores bound insect gut receptors.
• Germination rates increased threefold with insect gut membrane vesicles.

Conclusions:

• Cry toxins on B. thuringiensis spore surfaces are accessible for binding insect gut receptors.
• Surface-exposed toxins facilitate insect pathogenesis at the cost of spore resistance.
• A model proposes toxin protection by the exosporium in soil and exposure in the insect gut.