Bt Toxin Modification for Enhanced Efficacy

Abstract

Insect-specific toxins derived from Bacillus thuringiensis (Bt) provide a valuable resource for pest suppression. Here we review the different strategies that have been employed to enhance toxicity against specific target species including those that have evolved resistance to Bt, or to modify the host range of Bt crystal (Cry) and cytolytic (Cyt) toxins. These strategies include toxin truncation, modification of protease cleavage sites, domain swapping, site-directed mutagenesis, peptide addition, and phage display screens for mutated toxins with enhanced activity. Toxin optimization provides a useful approach to extend the utility of these proteins for suppression of pests that exhibit low susceptibility to native Bt toxins, and to overcome field resistance.

Bacillus thuringiensis targets the host intestinal epithelial junctions for successful infection of Caenorhabditis elegans

“…It is well‐documented that in insects and nematodes the midgut cell lysis can be caused by Bt Cry toxins alone through pore formation (Bravo et al ., ; Deist et al ., ; Dementiev et al ., ; Peng et al ., ). However, Cry toxins alone did not effectively disrupt the midgut epithelial junctions in C. elegans (Fig.…”

“…During sporulation, Bt produces parasporal crystal proteins (Cry) that have specific toxicity to different insects, nematode, mites and protozoa species (Schnepf et al, 1998;Pardo-Lopez et al, 2013). The Cry proteins are recognized as pore-forming toxins that effectively lyse the epithelial cells by osmotic shock, disrupting the midgut epithelium and killing the insect larvae (Bravo et al, 2007;Deist et al, 2014). In addition, Bt produces several other virulence factors important for its pathogenicity in insects (Raymond et al, 2010).…”

Toward mosquito control with a green alga: expression of Cry toxins of Bacillus thuringiensis subsp. israelensis (Bti) in the chloroplast of Chlamydomonas

“…Since we did not try expressing full-length cry4Aa , we cannot be certain that truncating the protein to 74 kDa increased protein levels, but it seems likely that it did. Truncating Cry1 proteins, which are also quite large, increased their expression and toxicity in higher plants (reviewed in Deist et al 2014). Hence, truncating cry4Ba may improve its expression, and an attempt to do that is underway in the laboratory.…”

Applications of Protein Engineering and Directed Evolution in Plant Research

“…Optimization of Bacillus thuringiensis toxin has been a focus of insect-specific pest control strategies. This optimization has been carried out in a variety of ways, for example, through truncation, domain swapping, peptide addition, and amino acid mutation (Deist et al, 2014). The most prevalent engineering goals addressed in these optimization approaches include increasing toxin potency to combat increasing pest resistance toward the toxins and expanding their applicability to a wider range of pests.…”