Aug 2, 2010

Research Projects

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Binding of Bt proteins to soil particles

(2008 – 2011) Institute of Applied Biotechnology in the Tropics (IBT) at the University of Göttingen

Topic

The aim of this project is to investigate the effects of the cultivation of the genetically modified Bt maize cultivar MON89034xMON88017, which produces three different Bt proteins, on the soil of the crop area. The Bt proteins from the maize plants enter the soil via root exudates, harvest residues and pollen and bind to soil particles. The binding (sorption) to soil particles partially inhibits the breakdown of the Bt proteins, so that their insecticidal effect remains intact. This could alter humus formation and the composition of the organic substance in the soil.

The project will examine the following questions:

• What are the chemical-physical properties of the soil fractions on the release site and of the three different Bt proteins produced by the maize variety under investigation?
• What quantities of Bt proteins are exuded via the roots and how quickly are they broken down?
• What binding behaviour do the Bt proteins exhibit towards the soil fractions on the release site?
• Do the three Bt proteins compete for binding sites in the soil?
• Is it likely that Bt proteins can be transported to lower soil layers over longer periods of time?

Experiment description

Characterisation of the soils and Bt toxins

The precursor projects showed that the binding of Bt proteins to soil particles is significantly affected by the structure and chemical properties of both the clay particles in the soil and the Bt proteins. Since this project is investigating a new genetically modified maize variety on a different release site, the soils and the Bt proteins must first be adequately characterised to serve as a basis for further studies.

Soil samples are taken from all the plots on the trial field and tested for their chemical properties and mineral composition.

Mass spectrometry is used to record differences in the molecular structure of the three Bt proteins. The proteins are ionised by laser and separated according to their mass/load ratio.

Examination of root exudates

Root exudates are obtained from genetically modified plants in a nutrient solution. The ELISA detection method is used to measure the concentration of the Bt proteins at different times and to determine the rate of breakdown.

Sorption measurements

Defined amounts of clay/fine earth and a Bt protein are shaken together for thirty minutes. The concentration of the Bt protein in the overlaying solution is then measured. The experiment is conducted with different starting concentrations of Bt protein, corresponding to the concentrations measured in the root exudates.

To check whether Bt proteins compete for binding sites, other sorption measurements are conducted with solutions containing all three Bt proteins.

Characterisation of the movement of the Bt proteins in the soil

In order to characterise the movement of the Bt proteins in the soil of the release site in greater detail, a solution containing Bt protein is poured through a column filled with soil from the trial field. The liquid that passes through is collected. Measurements are made to see how much Bt protein it still contains that has not been bound to soil particles. On the basis of these measurements, conclusions can be drawn about how much Bt protein could be transported to lower soil layers on the release site.

Production of antibodies

As part of the project, new antibodies for the different Bt proteins are being developed and produced. They are to be used in the ELISA test and made available to the whole of the research group.