HEMOLYSIN-II IS MORE CHARACTERISTIC OF BACILLUS-THURINGIENSIS THAN BACILLUS-CEREUS

To investigate the distribution of the hemolysin II determinant among strains of Bacillus cereus and Bacillus thuringiensis, thirteen strain s of B. cereus and fourteen strains of B. thuringiensis strains were t ested for hybridization of their chromosomal DNAs with a DNA probe con taining the B. cereus hemolysin II gene. In addition, the production o f hemolysin II, whose activity is not inhibited by cholesterol, was te sted. The presence (absence) of the hybridization response in the micr oorganism's genome correlated with the presence (absence) of cholester ol-unaffected hemolysin production. Only four out of thirteen B. cereu s strains were found to give a positive response in hybridization expe riments, whereas thirteen out of fourteen B. thuringiensis strains res ponded positively. DNAs from ten B. thuringiensis strains contained a 3.5 kb EcoRV fragment, which hybridized with the B. cereus hemolysin I I gene probe. The 3.5 kb EcoRV DNA fragment from one of these strains (B. thuringiensis VKM-B1555) was cloned and expressed in Escherichia c oli cells. The hemolysin encoded by the cloned DNA. fragment was not i nhibited by cholesterol and possessed all other properties of B. cereu s hemolysin II. The obtained data clearly show limited distribution of hemolysin II among B. cereus strains and demonstrate that hemolysin I I is more characteristic of B. thuringiensis than B. cereus.