Mobility of adsorbed Cry1Aa insecticidal toxin from Bacillus thuringiensis (Bt) on montmorillonite measured by fluorescence recovery after photobleaching (FRAP)

Abstract

The insecticidal toxins produced by genetically modified Bt crops are introduced into soil through root exudates and tissue decomposition and adsorb readily on soil components, especially on clays. This immobilisation and the consequent concentration of the toxins in “hot spots” could increase the exposure of soil organisms. Whereas the effects on non-target organisms are well documented, few studies consider the migration of the toxin in soil. In this study, the residual mobility of Bt Cry1Aa insecticidal toxin adsorbed on montmorillonite was assessed using fluorescence recovery after photobleaching (FRAP). This technique, which is usually used to study dynamics of cytoplasmic and membrane molecules in live cells, was applied for the first time to a protein adsorbed on a finely divided swelling clay mineral, montmorillonite. No mobility of adsorbed toxin was observed at any pH and at different degrees of surface saturation.

Keywords:

• Bacillus thuringiensis
• adsorption
• insecticidal protein
• Cry1Aa
• montmorillonite
• FRAP
• fluorescence recovery after photobleaching
• mobility
• horizontal transfer
• lateral diffusion

Acknowledgements

The research was funded by the Agence Nationale de la Recherche and a doctoral grant was awarded to N.H. by the INRA and the Région Languedoc Roussillon. The authors want to thank B. Chabi for her help with FRAP measurements, R. Frutos and M. Royer for providing the Bt strain and the cultivation-extraction protocol, W. Szponarski for purification technique, and F.X. Sauvage for protein analysis, LBE-INRA Narbonne for providing the fermentor and the INRA proteomic platform for mass spectroscopy analyses.