Fate and Effects in Soil of Cry Proteins from Bacillus thuringiensis: Influence of Physicochemical and Biological Characteristics of Soil

Abstract

Bacillus thuringiensis (Bt) is a useful alternative or supplement to synthetic chemical pesticides in agriculture, forest management, and control of mosquitoes and some other biting insects. When modified Bt cry genes are inserted into a plant species (e.g., corn, cotton, potato, canola, rice), the plant expresses active larvicidal proteins in its tissues. The toxins continue to be synthesized during growth of the plants, making the plant toxic to various insect pests throughout their life or as biomass incorporated into soil. If production exceeds consumption, inactivation, and degradation, the toxins could accumulate to concentrations that may enhance the control of target pests or constitute a hazard to nontarget organisms, such as the soil microbiota, beneficial insects (e.g., pollinators, predators and parasites of insect pests), and other animal classes. The accumulation and persistence of the toxins could also result in the selection and enrichment of toxin-resistant target insects. Persistence is enhanced when the toxins are bound on surface-active particles in the environment (e.g., clays and humic substances) and, thereby, rendered more resistant to biodegradation while retaining toxic activity. Moreover, major problem we face today is of "Molecular pharming" that utilizes transgenic plants and animals for production of pharmaceuticals and chemicals for their use in human beings and industries respectively. Their release to the environment, especially to soil and potentially to waters of the pharmaceutical and industrial products of transgenic plant and animal "pharms" could pose a hazard to the environment. In contrast to the products of most transgenic plants currently available commercially (e.g., the insecticidal proteins from subspecies of Bt) that primarily target insects and other pests. These "pharms" are being genetically engineered to express products for use primarily in human beings. Consequently, these products constitute a class of compounds that is seldom found in natural habitats and that primarily target "higher level" eukaryotes. Hence, they are xenobiotics with respect to the environment, and their persistence in and effects on the environment have not been adequately studied and sober risk assessments on a case-by- case basis must be made before major releases of such transgenic organisms.