COMPARATIVE-STUDIES OF GROWTH CHARACTERISTIC AND COMPETITIVE ABILITY IN BACILLUS-THURINGIENSIS AND BACILLUS-CEREUS IN SOIL

We examined the growth characteristics and competitive abilities of Ba cillus thuringiensis and Bacillus cereus in soil. The growth and persi stence of the two bacilli, added to sterile soil with or without soil bacteria, were monitored under aerobic conditions. When vegetative cel ls or spores of B. thuringiensis and/or B. cereus were added to steril e soil, both bacilli increased their numbers. The final levels of popu lation were greater for B. cereus than for B. thuringiensis. In most o f the cases when vegetative cells of B. thuringiensis were added at th e same time as indigenous soil bacteria to sterile soil, B. thuringien sis sporulated immediately without any growth. B. thuringiensis grew o nly when both B. thuringiensis and indigenous soil bacteria were inocu lated at low densities. On the other hand, when vegetative cells or sp ores of B. cereus were added at the same time as indigenous soil bacte ria to sterile soil, B. cereus grew even when indigenous soil bacteria were inoculated at high density. These data suggest that B. thuringie nsis is less adaptive to soil habitats than B. cereus.