Bacillus brevis Migula 1900 taxonomy: reassociation and base composition of DNA

Of 87 strains previously identified as Bacillus brevis Migula 1900, 58 had G + C contents of 47.0 to 51.9 mol%, a range that included the G + C content (48.7 mol%) of the type strain. The G + C contents for three other groups consisting of 5, 7, and 17 strains were 37.0 to 41.9, 42.0 to 46.9, and 52.0 mol% or higher, respectively. DNA reassociation studies showed that 25 of the 58 strains with G + C contents of 47.0 to 51.9 mol% were closely related genetically to the type strain and to each other. For the most part, this genetically related group was phenotypically homogeneous; variations in the fermentation of mannitol and mannose were observed. My results strongly suggest that many of the strains were misclassified as B. brevis. Consequently, much of the phenotypic heterogeneity of the species B. brevis Migula 1900 is not due to variations exhibited by genetically related organisms, but is the result of variability introduced by the presence of genetically unrelated strains.