Adsorption of Transgenic Insecticidal Cry1Ab Protein to Silica Particles. Effects on Transport and Bioactivity

Abstract

Bt crops are genetically modified to be resistant against insect pests by expressing insecticidal Cry proteins. The processes governing the fate and bioavailability of the expressed transgenic Cry proteins in soils are poorly understood. We studied adsorption of Cry1Ab to negatively charged silica (SiO(2)) particles, a major soil constituent and a model for negatively charged mineral surfaces, at pH 5 to 10 and ionic strengths I = 10 mM to 250 mM, both in solution depletion and saturated column transport experiments. Cry1Ab-SiO(2) interactions were dominated by patch-controlled electrostatic attraction (PCEA), as evident from increasing Cry1Ab attraction to SiO(2) with decreasing I at pH at which both Cry1Ab and SiO(2) were net negatively charged. Experimental and modeling evidence is provided that the surface heterogeneity of SiO(2) particles modulated PCEA, leading to a fraction of adsorption sites with slow Cry1Ab desorption kinetics. Desorption rates from these sites increased upon increasing the solution pH. In toxicity bioassays, we demonstrated that Cry1Ab retained insecticidal activity when adsorbed to SiO(2), suggesting high protein conformational stability during adsorption-desorption cycles. Models predicting Cry1A protein adsorption in soils therefore need to account for combined effects of the nonuniform protein surface charge distribution and of sorbent surface heterogeneity.

Fate of Bacillus thuringiensis subsp. israelensis in the Field: Evidence for Spore Recycling and Differential Persistence of Toxins in Leaf Litter

“…This profile of decreased detectability of toxins is congruent with previous studies which investigated the fate of soluble Cry3 and Cry1 toxins in different soils (1,19,21,30). It seems that the heterogeneous structure of the leaf litters is close to the structure of soils, generating the same toxin adsorption profiles (25). In the present work, we used toxins in their crystal form instead of soluble toxins, and we obtained similar results.…”

Attachment of Pathogenic Prion Protein to Model Oxide Surfaces

“…29 Such congruence between more traditional techniques and QCM-D and OWLS was recently highlighted in a study examining adsorption of transgenic insecticidal crystal (Cry) proteins derived from Bacillus thuringiensis to SiO 2 . 60 The areal surface densities for pathogenic PrP attaching to SiO 2 in the present study were lower than those previously reported by Johnson et al 27 This discrepancy is likely due primarily to limitations in the detection method applied in the earlier study. We find that solution chemistry strongly impacts prion attachment to SiO 2 surfaces.…”

Decreased Toxicity of Bacillus thuringiensis subsp. israelensis to Mosquito Larvae after Contact with Leaf Litter

“…It has been shown that Cry toxins bound to the soil (37) or to leaf litter (present study) conserve their entire antigenicity and insecticidal activity. However, Cyt toxins have very different 3D conformations than Cry toxins and may interact differently with the heterogenic sorbent surface of the leaf litter, explaining why they partly lose their immunological detectability and synergistic effects (26). Even if the toxin extraction protocol coupled with ELISAs showed good efficiency and reproducibility for all toxins (see Fig.…”