CLARIFICATION OF THE TAXONOMY OF BACILLUS MYCOIDES

Because of the very similar physiological properties and base sequences of the 16S rRNAs of Bacillus cereus, Bacillus mycoides, and Bacillus thuringiensis, some taxonomists question the validity of separating these organisms into distinct species, DNA relatedness studies based on spectrophotometrically measured renaturation rates were carried out to determine the taxonomic relationships of the three species, A study of 58 strains revealed that the levels of relatedness between B, cereus and B. mycoides and between B. cereus and B, thuringiensis ranged from 22 to 44% and from 59 to 69%, respectively. On the basis of the moderately high Levels of DNA relatedness which we determined, B. cereus and B, thuringiensis appeared to be genetically related but taxonomically distinct entities. The B. mycoides group was genetically distantly related to the B. cereus group and represented a separate taxon. Furthermore, our data indicated that the B. mycoides group consists of two genetically distinct groups, each of which represents a distinct species, In addition to rhizoidal colonial morphology and lack of motility, the B. mycoides group could be distinguished from B. cereus by differences in fatty acid profiles and acetanilide-producing activities.