Cry1Ab/Ac proteins released from subspecies of Bacillus thuringiensis (Bt) and transgenic Bt-rice in different paddy soils

As Bacillus thuringiensis (Bt) are entomopathogenic bacteria for use as biological insecticide and serve as a main source for genetically modified crops, it is imperative to investigate fate of Bt-toxins (Cry-proteins) released in soil. Four differently textured paddy soils, i.e. sandy loam, loam, silt loam and silty clay, were selected to investigate production and release of Cry-proteins by two Bt-strains (subspecies thuringiensis and kurstaki) and by transgenic Bt-rice (cultivar TT51-1). After amended with Cry-proteins, soil can adsorb proteins while sorption rate was variable among different paddy soils, with the highest amount of Cry-proteins in the silty clay soil. During the period of incubation with Bt-strains, the silty clay soil showed significant accumulation of Cry-proteins. Additionally, level of Cry-protein production was different between two Bt-strains. Inactivation of indigenous microorganisms in the soil samples led to slightly higher production of Cry-proteins by Bt-strains in all four soil types. Cry-proteins were released via root exudates of transgenic Bt-rice in sterile hydroponic culture and in non-sterile soils throughout the growth of plants. Protein release significantly varied among different paddy soils, up to 34.9 ng Cry-proteins g(-1) soil in clayey soil. It indicates differently textured paddy soils reflect variable sorption, persistence, and accumulation of Cry-proteins.