Mineralization of the bacillus thuringiensis Cry1Ac endotoxin in soil

Although a number of studies have been done describing the fate of Bacillus thuringiensis insecticidal endotoxins in soil, there is conflicting information on the persistence of this class of insecticidal toxins. This is partly due to methodological limitations in many of the previous studies. In the experiments reported here, ¹⁴C-labeled B. thuringiensis CrylAc endotoxin was used to study its mineralization in soil incubated under controlled conditions. Fifty-nine percent of the radiolabeled CrylAc was recovered as ¹⁴CO ₂ at the end of the 20 day incubation period. The addition of 4.5% corn residues stimulated mineralization of [ ¹⁴C]Cry1Ac toxin, and mineralization of glucose was 3.6 times faster than that of the CrylAc toxin, indicating that the soil was microbiologically and metabolically active. Because only low mineralization (approximately 6%) of the radiolabeled toxin was observed in autoclaved soil, the current findings indicate that microbial processes play a major role in the dissipation of the CrylAc endotoxin in soil. The results of this study suggest that there may be limited risk of the bioaccumulation of CrylAc in soil due to the eventual release of this insecticidal toxin by Bt-protected crops.