title: Adsorption of insecticidal Cry1Ab protein to humic substances. 1. Experimental approach and mechanistic aspects.
abstract: Adsorption is a key process affecting the fate of insecticidal Cry proteins (Bt toxins), produced by genetically modified Bt crops, in soils. However, the mechanisms of adsorption to soil organic matter (SOM) remain poorly understood. This work assesses the forces driving the adsorption of Cry1Ab to Leonardite humic acid (LHA), used as a model for SOM. We studied the effects of solution pH and ionic strength (I) on adsorption using a quartz crystal microbalance with dissipation monitoring and optical waveguide lightmode spectroscopy. Initial Cry1Ab adsorption rates were close to diffusion-limited and resulted in extensive adsorption, even at pH >6, at which LHA and Cry1Ab carry negative net charges. Adsorption increased with decreasing I at pH >6, indicating Cry1Ab-LHA patch-controlled electrostatic attraction via positively charged domains of Cry1Ab. Upon rinsing, only a fraction of Cry1Ab desorbed, suggesting a range of interaction energies of Cry1Ab with LHA. Different interaction energies likely resulted from nonuniformity in the LHA surface polarity, with higher Cry1Ab affinities to more apolar LHA regions due to the hydrophobic effect. Contributions from the hydrophobic effect were substantiated by comparison of the adsorption of Cry1Ab and the reference proteins albumin and lysozyme to LHA and to apolar and polar model surfaces.
authors.affiliation: Institute of Biogeochemistry and Pollutant Dynamics (IBP), Swiss Federal Institute of Technology, ETH Zurich, Zurich, Switzerland. michael.sander@env.ethz.ch
authors.forename: Michael
authors.initials: M
authors.lastname: Sander
authors.forename: Jeanne E
authors.initials: JE
authors.lastname: Tomaszewski
authors.forename: Michael
authors.initials: M
authors.lastname: Madliger
authors.forename: René P
authors.initials: RP
authors.lastname: Schwarzenbach
mesh_terms: D000327:Adsorption; D001413:Bacillus thuringiensis / Q000302:isolation & purification; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000302:isolation & purification*; D004731:Endotoxins / Q000302:isolation & purification*; D006460:Hemolysin Proteins / Q000302:isolation & purification*; D006812:Humic Substances / Q000032:analysis*; D007306:Insecticides / Q000302:isolation & purification*; D008903:Minerals / Q000032:analysis*; D008958:Models, Molecular; D058525:Quartz Crystal Microbalance Techniques
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; D006812:Humic Substances; D007306:Insecticides; D008903:Minerals; C030956:insecticidal crystal protein, Bacillus Thuringiensis; C568542:leonardite