Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2007
Publication Date: 1/9/2008
Citation: Accinelli, C., Koskinen, W.C., Becker, J.M., Sadowsky, M.J. 2008. Mineralization of the Bacillus thuringiensis Cry1Ac endotoxin in soil. Journal of Agricultural and Food Chemistry. 56:1025-1028.
Interpretive Summary: Research has shown that genetically modified crops can exude insecticidal chemicals (Bt Cry toxins) from roots into the soil or release the toxins through decomposition of crop residues. In recent years, concerns dealing with the impact of Cry toxins on the soil ecosystem have been expressed in public and scientific debate, but have not yet been adequately addressed. Results from the present study clearly illustrate that the Bt toxin is degraded by the soil microbial community and does not persist within the soil as has been previously reported by other researchers. Our results clearly illustrate the fact that the Bt toxin eventually released into the soil by incorporation of plant residues and/or root exudation of GM crops is actively degraded by the soil microbial community rather than persisting for several months. This study demonstrates that there would be no risk of bioaccumulation of the Cry1Ac toxin in soil eventually released by Bt-protected crops and that producers can safely use these crops.
Technical Abstract: Despite a number of studies describing the fate of Bacillus thuringiensis insecticidal endotoxins in soil have been conducted in the past decade, conflicting information on persistence of this class of insecticidal toxins exists. In the present experiment, 14C from glucose was incorporated into the B. thuringiensis Cry1Ac endotoxins and radiolabeled toxin was used to study its mineralization in soil samples incubated under controlled conditions. Fifty-nine percent of the radiolabeld Cry1Ac was recovered as 14CO2 at the end of the 20-day incubation period. Addition of 4.5% of corn residues stimulated mineralization of [14C]Cry1Ac toxin. Since low mineralization (approximately 6%) of the radiolabeled toxin was observed in autoclaved soil, our findings indicate a major role of microbial processes in the dissipation of the Cry1Ac endotoxin. This study demonstrates that there would be no risk of bioaccumulation of Cry1Ac in soil eventually released by Bt-protected crops.