title: Adsorption of insecticidal Cry1Ab protein to humic substances. 2. Influence of humic and fulvic acid charge and polarity characteristics.
abstract: Assessing the fate and potential risks of transgenic Cry proteins in soils requires understanding of Cry protein adsorption to soil particles. The companion paper provided evidence that patch-controlled electrostatic attraction (PCEA) and the hydrophobic effect contributed to Cry1Ab protein adsorption to an apolar humic acid (HA). Here, we further assess the relative importance of these contributions by comparing Cry1Ab adsorption to seven humic substances varying in polarity and charge, at different solution pH and ionic strength, I. Cry1Ab adsorption to relatively apolar HAs at I = 50 mM exhibited rapid initial rates, was extensive, and was only partially reversible at pH 5-8, whereas adsorption to more polar fulvic acids was weak and reversible or absent at pH >6. The decrease in adsorption with increasing HS polarity at all tested pH strongly supports a large contribution from the hydrophobic effect to adsorption, particularly at I = 50 mM when PCEA was effectively screened. Using insect bioassays, we further show that Cry1Ab adsorbed to a selected HA retained full insecticidal activity. Our results highlight the need to consider adsorption to soil organic matter in models that assess the fate of Cry proteins in soils.
authors.affiliation: Swiss Federal Institute of Technology, ETH Zurich, Institute of Biogeochemistry and Pollutant Dynamics (IBP), Zurich, Switzerland.
authors.forename: Jeanne E
authors.initials: JE
authors.lastname: Tomaszewski
authors.forename: Michael
authors.initials: M
authors.lastname: Madliger
authors.forename: Joel A
authors.initials: JA
authors.lastname: Pedersen
authors.forename: René P
authors.initials: RP
authors.lastname: Schwarzenbach
authors.forename: Michael
authors.initials: M
authors.lastname: Sander
mesh_terms: D000327:Adsorption; D001413:Bacillus thuringiensis / Q000737:chemistry / Q000302:isolation & purification; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry / Q000302:isolation & purification*; D001578:Benzopyrans / Q000032:analysis*; D004731:Endotoxins / Q000737:chemistry / Q000302:isolation & purification*; D006460:Hemolysin Proteins / Q000737:chemistry / Q000302:isolation & purification*; D006812:Humic Substances / Q000032:analysis*; D057927:Hydrophobic and Hydrophilic Interactions; D007306:Insecticides / Q000737:chemistry / Q000302:isolation & purification*; D008958:Models, Molecular; D009994:Osmolar Concentration; D055672:Static Electricity
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001578:Benzopyrans; D004731:Endotoxins; D006460:Hemolysin Proteins; D006812:Humic Substances; D007306:Insecticides; C030956:insecticidal crystal protein, Bacillus Thuringiensis; C005023:fulvic acid