Intrageneric clustering and divergence of Erwinia strains from plants and man in the light of deoxyribonucleic acid segmental homology.

Abstract

The relationships among Erwinia species (originating from plants and man) and other enterobacteria were examined in terms of DNA–DNA segmental homology. All of the organisms studied show a "core homology" amounting to about 10–15%, thus supporting the inclusion of the erwinias in the taxonomic vicinity of the other enterobacteria, and also revealing that the present genus Erwinia is hardly separable from the other enterobacterial genera solely on the extent of DNA–DNA segmental homology. Genetic clusters based on DNA–DNA segmental homology are found within all of Dye's "natural" (phenotypic) groups of the genus Erwinia. However, these genetic clusters are not coextensive with any entire natural group, and designation of any of them as genera seems implausible at present. Except for a few cases of obvious synonymy, the several Erwinia nomenspecies generally showed significant nomen-species-specific segments of DNA, but a taxonomic revision at the species level based only on DNA–DNA segmental homology would seem premature. The Erwinia strains isolated from human clinical sources are essentially indistinguishable on the basis of DNA–DNA segmental homology from the epiphytic and related Erwinia strains derived from plants.