title: 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.
authors.affiliation: Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zurich, Zurich, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Madliger
authors.forename: Christoph A
authors.initials: CA
authors.lastname: Gasser
authors.forename: René P
authors.initials: RP
authors.lastname: Schwarzenbach
authors.forename: Michael
authors.initials: M
authors.lastname: Sander
mesh_terms: D000327:Adsorption; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000032:analysis / Q000737:chemistry*; D004731:Endotoxins / Q000032:analysis / Q000737:chemistry*; D019015:Geologic Sediments / Q000737:chemistry; D006460:Hemolysin Proteins / Q000032:analysis / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D009994:Osmolar Concentration; D010572:Pest Control, Biological; D030821:Plants, Genetically Modified; D012822:Silicon Dioxide / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; D012989:Soil Pollutants; C030956:insecticidal crystal protein, Bacillus Thuringiensis; D012822:Silicon Dioxide