Benjamin Deist from Iowa State University's Department of Entomology will be defending his thesis as a part of the spring semester seminar series. This Master's defense seminar will be located in E164 Lagomarcino Hall.
Abstract. A major group of toxins produced by Bacillus thuringiensis (Bt) is comprised of the Crystal (Cry) toxins. Cry toxins require proteolytic activation and the activated toxin binds to the gut epithelium causing mortality in the insect host. A lack of proteolytic activation or lack of binding has been associated with limited efficacy of Cry toxins. Insects in the order Hemiptera, which includes pests of agricultural significance such as aphids, have low susceptibility to Cry toxins. Cry4Aa with a low level of activity against the pea aphid (Acyrthrosiphon pisum), is an ideal candidate for modification to enhance activity towards other aphid species, such as the soybean aphid (Aphis glycines). A phage display library was screened in vivo to isolate peptides that bind the soybean aphid gut. In vitro binding of the selected peptides was characterized and the strongest binding peptide was used to engineer Cry4Aa. The modified toxins were assessed for stability and for toxin activity against soybean aphids.