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Adsorption of the insecticidal protein of Bacillus thuringiensis subsp. kurstaki by minerals: effects of inorganic salts

Fu, Qingling, Wang, Wanqin, Hu, Hongqing, Chen, Shouwen
European journal of soil science 2008 v.59 no.2 pp. 216-221
Bacillus thuringiensis subsp. kurstaki, adsorption, edaphic factors, goethite, inorganic salts, insecticidal proteins, ions, kaolinite, mineral soils, montmorillonite, salt concentration, silica, toxins
The persistence of the insecticidal protein of Bacillus thuringiensis (Bt) is enhanced by the reactivity with soil particles and may constitute a hazard to the soil ecosystem; however, studies on the fate of the Bt toxin in soil, especially in the presence of inorganic salts, are limited. The effects of different concentrations of KNO₃, KH₂PO₄ and NH₄H₂PO₄ on the adsorption of Bacillus thuringiensis toxin by kaolinite, montmorillonite, goethite and silicon dioxide were investigated. Results showed that small salt concentrations tended to enhance toxin adsorption, whereas large concentrations (> 10 mmol litre⁻¹) inhibited sorption. Similar results were observed regardless of the order in which toxin and inorganic salt were added. The degree to which individual salts affected adsorption decreased in the sequence for minerals, goethite > kaolinite >= montmorillonite > silicon dioxide, and for ions, H₂PO₄⁻ > NO₃⁻, NH₄⁺ > K⁺. Our results indicate that inorganic salts can markedly influence the adsorption of Bt toxin by soil minerals. This investigation will help in evaluating the behaviour and fate of Bt toxins in the soil environment.