Effect of incubation in non-sterilised and autoclaved arable soil on survival ofBacillus thuringiensisandBacillus cereusspore inocula

Abstract

Abstract Inocula of 103, 104, and 105 Bacillus thuringiensis spores/g non-sterilised soil apparently failed to germinate and viability declined by up to 55% during 90 days incubation at 25°C and -0.10 MPa. In autoclaved (121°C, 20 min) soil, no net mortality was detected in any of the 3 levels of inocula and detection of germination was erratic. No germination was detected yet sporadic growth occurred with inocula of 103 spores/g soil, and both (sporadic) germination and growth were detected at 104 spores/g soil. Final levels of these inocula were 500–2000% greater than their initial levels. Germination and growth were not detected in the inoculum of 105 spores/g soil. By contrast, inocula of 104 Bacillus cereus spores/g germinated in both non-sterilised and autoclaved soil, but then exhibited bacteriostasis. No net changes in inoculum size were detected in either soil treatment. We suggest that the mortality of B. thuringiensis spores in non-sterilised soil resulted from an inherent inability of the spor...