Evolution and taxonomy in the genus Brucella: contemporary evolutionary status of the species Brucella abortus.

The biotypes in the species Brucella abortus were arranged according to the sequential flow in the alterations of their characteristics. This reordering of the biotypes indicated that the organism currently classified as B abortus type 2 is the parent organism of all the biotypes in this species. However, laboratory-selected mutants from B abortus type 2 had characteristics that were mimetic, but not duplicative, of their naturally occuring counterparts. Evidence which indicates this phenomenon is related to permeability of the cell wall is presented and discussed.