Subproject: Validation of a bioassay with nematodes to assess bioavailability and toxicity of Bt toxins in soil.
Aim of the project

According to EU guidelines (2001/18/EG), the release of genetically modified plants (GM-Plants) requires an environmental risk assessment in order to assess potential direct or indirect, acute or chronic impact on the environment in a case-specific manner. By growing genetically modified Bt-maize that is resistant to certain pest by producing pest-specific Bt-toxins, also non-target organisms might be harmed. If Bt-toxins pose a risk to non-target organisms, depends on the protein structure of the Bt-toxin (Cry protein), the type of soil on which the plant is grown and the susceptibility of the organisms. Therefore, this risk can only be evaluated using bioassays with soil organisms. In this subproject, a toxicity test using the nematode Caenorhabditis elegans was validated as a risk assessment tool. Within the joint research project “Freisetzungsbegleitende Sicherheitsforschung transgener Maissorten mit neuen Bt-Genen: Entwicklung und Validierung von Monitoringmethoden” the validation was exemplarily exercised based on the Bt-maize Mon863, producing the toxin Cry3Bb, which is toxic agains the Western corn rootworm (Diabrotica virgifera virgifera). A standardized test method (ISO 10872) using the nematode Caenorhabditis elegans allowed for a quick and cost effective toxicity assessment of bioavailable Bt-toxins in soil samples. Moreover, nematodes represent a highly relevant organism group for agro-ecosystems.

Following main goals were pursued in this subproject:

• Investigation of bioavailability and toxicity of Bt-toxins for C. elegans: Laboratory experiments with purified Bt-toxins in various test matrices (water, soil), revealed information on the bioavailability and toxicity of Cry3Bb1 for nematodes.
• Validation of a ecotoxicological tool for assessing the toxicity of Bt-toxin contaminated soil: Soil from fields that were cultivated with Bt- and non-Bt-maize over a period of two years were investigated for their toxicity. The aim was to provide a cost effective tool to assess the risk of Bt-toxins for relevant soil organisms.
• Effects of Bt-maize cultivation on in situ nematode communities: After two years of cultivation, in situ nematodes were sampled from fields with Bt- and non-Bt-maize over a whole cultivation period to assess effects under real, ecologically relevant conditions.

Publications originating from this project:

Höss S, Arndt M, Baumgarte S, Tebbe C, Nguyen-Thu H, Jehle J (2008) Effects of transgenic corn and Cry1Ab toxin on the nematode Caenorhabditis elegans. Ecotoxicol Environ Saf 70, 334-340.

Höss S, Nguyen-Thu H, Menzel R, Pagel-Wieder S, Miethling-Graff R, Tebbe CC, Jehle J, Traunspurger W (2011) Assessing the risk posed to free-living soil nematodes by a genetically modified maize (event Mon88017) expressing an insecticidal protein (Cry3Bb1). Sci Tot Environ 409:2674-2684.