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

The insecticidal toxin encoded by the cryl Ab gene from Bacillus thuringien sis was released in root exudates from transgenic Bt corn during 40 days of growth in soil amended to 0, 3, 6, 9, or 12% (v/v) with montmorillonite or kaolinite in a plant growth room and from plants grown to maturity in the field. The presence of the toxin in rhizosphere soil was determined by immu nological and larvicidal assays. No toxin was detected in any soils from is ogenic non-Bt corn or without plants. Persistence of the toxin was apparent ly the result of its binding on surface-active particles in the soils, whic h reduced the biodegradation of the toxin. The release of the toxin could e nhance the control of insect pests or constitute a hazard to nontarget orga nisms, including the microbiota of soil, and increase the selection of toxi n-resistant target insects. (C) 2000 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.