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Pesticide Toxicology Laboratory

ISU Entomology / Pesticide Toxicology Laboratory / Insecticidal toxin from Bacillus thuringiensis is released from roots of transgenic Bt corn in vitro and in situ

Insecticidal toxin from Bacillus thuringiensis is released from roots of transgenic Bt corn in vitro and in situ

Authors: Saxena, D., Stotzky, G.
Journal, Volume, Year: FEMS Microbiology Ecology, volume 33:35-39, 2000
Summary

Seeds of Bt corn (NK4640Bt) and the isogenic strain were planted in test tubes containing Kitchawan soil amended or not amended with kaolinite or montmorillonite. Soil was collected after 10, 20, 30, and 40 days of growth and analyzed by immunological and larvicidal assays. All samples were positive for the presence of Bt toxin and all samples were toxic to larvae tobacco hornworm. In addition, a field study was conducted in which seeds of Bt corn were planted in a sandy loam soil. Rhizosphere soil was collected after plants produced ears of corn and several months after the death of the plant. Immunological and larvicidal assays were positive for all rhizosphere soil samples collected from Bt corn, including those collected several months after the death of the plant.

Comments

Bt toxin was present in soil samples, but was only measured qualitatively using the Lateral Flow Quickstix. The authors acknowledge that some of the toxin detected in the field study was probably released in sloughed and damaged root cells but the major portion was derived from exudates. As in many other studies using the larvicidal assay, although toxicity is seen, the ecological relevance is unknown. Because soil solutions are placed in food, test organisms are forced to eat the Bt toxin; however, non-target organisms may or may not directly ingest Bt toxin.