Phylogenetic relationships of Anaplasma marginale and 'Ehrlichia platys' to other Ehrlichia species determined by GroEL amino acid sequences.

The heat-shock protein (GroEL) genes of Anaplasma marginale, Ehrlichia muris and 'Ehrlichia platys' were sequenced and compared with the GroEL of other species of Ehrlichia. The GroEL amino acid sequences of A. marginale and 'E. platys' were most similar to the GroEL sequence of Ehrlichia phagocytophila, with which they formed one group with 6-10% divergence. The E. muris GroEL was most closely related to the GroEL of two unclassified strains (HF-565 and Anan), then to Ehrlichia chaffeensis, Ehrlichia canis, Ehrlichia ewingii and Cowdria ruminantium, forming a second distinct group (0.3-8.6% divergence). The GroELs of Ehrlichia risticii and Ehrlichia sennetsu were very similar to one another (only 2% divergence), forming the third group. The first two groups were relatively closely related (17-20% divergence), while the third group was only distantly related to the first two groups (62-73% divergence).