Deoxyribonucleic Acid Homologies Among Strains of Bacillus sphaericus

The genetic relatedness of 62 strains of Bacillus sphaericus, 4 strains of B. pasteurii, 6 strains of B. brevis, and 1 strain each of B. globisporus and B. aminovorans was examined by deoxyribonucleic acid (DNA) homology. Five homology groups were identified, and they contained all but 12 of the B. sphaericus strains. Intergroup homologies ranged from about 20 to 40% except for groups III and IV, which had 50 to 60% intergroup homology. Although a few strains within some groups had 63 to 69% homology to the reference strain, most strains were in the 70 to 90% range. Homology group I contained the type of strain of B. sphaericus, ATCC 14577, and three other strains. Homology group II was subdivided into groups IIA and IIB, the former containing all of the strains found to be pathogenic for mosquito larvae. Although none of the physiological characteristics or combination of characteristics examined allowed the complete differentiation of strains into the appropriate homology groups, the strains of group I could be distinguished from those of group IIA-IIB. The strains of group IIA could be distinguished from all others by mosquito pathogenicity. The B. pasteurii strains formed a distinct homology group, although the guanine plus cystosine contents of their DNAs fell within the range of 34 to 37 mol% found for the 45 strains of B. sphaericus examined for this property. The B. brevis strains possessed a higher guanine plus cystosine content, and their DNAs were unrelated to the DNAs of the B. sphaericus reference strains tested.