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Peritrophic membrane contribution to Bt Cry delta-endotoxin susceptibility in Lepidoptera and the effect of
Johanna S Rees1, Paul Jarrett, David J Ellar
1Department of Biochemistry, Tennis Court Road, University of Cambridge, Cambs CB21GA, UK. jsr31@cam.ac.uk
Abstract:
In an effort to determine a reason for differing susceptibilities to Bacillus thuringiensis (Bt) Cry delta-endotoxins amongst lepidopteran species, the peritrophic membrane (PM), and a number of agents that target the PM, were investigated to determine their effect on the efficacy of Bt toxins. In particular Calcofluor is able to disrupt the PM that acts as a barrier to microorganisms. Although Bt toxins have been shown to traverse the PM in some lepidopteran species, new data shows that toxins can bind the PM. Lepidopteran larval PMs also vary in thickness and composition that may determine the passage of Bt toxins. In non-susceptible insects the toxin associates with PM proteins and frass and is thought to be retained by the PM and then excreted before binding to the exposed target midgut membrane. However, the addition of Calcofluor to Bt toxins at an LC50 for the recipient species did not result in an increase in the efficacy of the toxin. It is evident that Calcofluor does disrupt the PM but the toxin preferentially binds PM fragments and is excreted instead of binding the exposed target midgut membrane, therefore having little toxic effect. This study therefore concludes that Calcofluor is not as suitable as other toxin enhancing agents such as chitinase.
Insights
Bacillus thuringiensis (Bt) Cry toxins target lepidopteran pests. Calcofluor disrupts the peritrophic membrane (PM), but does not enhance Bt toxin efficacy, as toxins bind to PM fragments instead.
Area of Science:
- Entomology
- Insect toxicology
- Biochemistry
Background:
- Lepidopteran species exhibit varying susceptibility to Bacillus thuringiensis (Bt) Cry delta-endotoxins.
- The peritrophic membrane (PM) acts as a barrier, influencing Bt toxin efficacy.
- Bt toxins can bind to the PM, and PM composition/thickness may affect toxin passage.
Purpose of the Study:
- Investigate the role of the peritrophic membrane (PM) and agents targeting it in Bt toxin efficacy.
- Determine if disrupting the PM with Calcofluor enhances Bt Cry delta-endotoxin activity in lepidopteran larvae.
- Compare the efficacy of Calcofluor with other potential toxin-enhancing agents.
Main Methods:
- Investigated the peritrophic membrane (PM) and its interaction with Bt Cry delta-endotoxins.
- Utilized Calcofluor to disrupt the PM in lepidopteran larvae exposed to Bt toxins.
- Assessed the efficacy of Bt toxins with and without Calcofluor at a determined LC50 concentration.
Main Results:
- Calcofluor disrupts the peritrophic membrane (PM) but does not increase Bt toxin efficacy.
- Bt toxins preferentially bind to PM fragments when Calcofluor is present, leading to excretion.
- The disruption of the PM by Calcofluor prevents toxin binding to the target midgut membrane.
Conclusions:
- Calcofluor is not an effective agent for enhancing Bt Cry delta-endotoxin efficacy.
- The mechanism of Bt toxin action is hindered by Calcofluor-induced PM disruption and subsequent toxin excretion.
- Chitinase is suggested as a more suitable agent for enhancing Bt toxin activity compared to Calcofluor.
