Comparative Studies of Growth Characteristic and Competitive Ability in Bacillus thuringiensis and Bacillus cereus in Soil

Abstract

We examined the growth characteristics and competitive abilities of Bacillus thuringiensis and Bacillus cereus in soil. The growth and persistence of the two bacilli, added to sterile soil with or without soil bacteria, were monitored under aerobic conditions. When vegetative cells or spores of B. thuringiensis and/or B. cereus were added to sterile soil, both bacilli increased their numbers. The final levels of population were greater for B. cereus than for B. thuringiensis. In most of the cases when vegetative cells of B. thuringiensis were added at the same time as indigenous soil bacteria to sterile soil, B. thuringiensis sporulated immediately without any growth. B. thuringiensis grew only when both B. thuringiensis and indigenous soil bacteria were inoculated at low densities. On the other hand, when vegetative cells or spores of B. cereus were added at the same time as indigenous soil bacteria to sterile soil, B. cereus grew even when indigenous soil bacteria were inoculated at high density. These data suggest that B. thuringiensis is less adaptive to soil habitats than B. cereus.