Survival and conjugation of Bacillus thuringiensis in a soil microcosm

The survival and conjugation ability of sporogenic and asporogenic Bacillus thuringiensis strains were investigated in broth, in non-amended sterile c lay soil monoculture and in mixed soil culture. The 75 kb pHT73 plasmid car rying an erythromycin resistance determinant and a cry1Ac gene was transfer red in mating broth and soil microcosm. Survival of strains was assessed in soil monoculture and in mixed soil culture for up to 20 days. Sporogenic s trains rapidly formed viable spores which were maintained until the end of the experiment. The asporogenic strains were no longer recovered after 8 da ys of incubation. This study shows that the environmental impact of asporog enic B. thuringiensis strains is lower than that of sporogenic B. thuringie nsis strains. Thus, the use of asporogenic strains may significantly reduce any potential risk (gene transfer, soil and plant contamination) due to th e dissemination of B. thuringiensis-based biopesticides in the environment. (C) 2000 Federation of European Microbiological Societies. Published by El sevier Science B.V. All rights reserved.