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 muri s and 'Ehrlichia platys' were sequenced and compared with the GroEL of othe r species of Ehrlichia. The GroEL amino acid sequences of A. marginale and 'E. platys' were most similar to the GroEL sequence of Ehrlichia phagocytop hila, 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 e wingii and Cowdria ruminantium, forming a second distinct group (0.3-8.6% d ivergence). The GroELs of Ehrlichia risticii and Ehrlichia sennetsu were ve ry similar to one another (only 2% divergence), forming the third group. Th e first two groups were relatively closely related (17-20% divergence), whi le the third group was only distantly related to the first two groups (62-7 3% divergence).