Phylogenetic analysis based on groE shows the closest evolutionary relationship between mitochondria and Rickettsia]

The nucleotide sequence of the groE operon of Rickettsia prowazekii, the obligate intracellular parasite of eukaryotes, was determined. The alignment of DNA-inferred amino acid sequences of the Hsp10 and Hsp60 heat-shock proteins with bacterial and mitochondrial homologues revealed the presence within Hsp60 of signatures shared by mitochondria and rickettsiae. Phylogenetic analysis demonstrated that heat-shock proteins of R. prowazekii are the earliest and the least diverging homologues within the family Rickettsiaceae--a sister group to the monophyletic clade of mitochondria. These results are in good agreement with the data obtained when using other molecular chronometers and show the closest relationship between mitochondria and Rickettsia. The possible nature of obligate intracellular parasitism of rickettsiae has been considered on the basis of the assumption that they and mitochondria could have a common evolutionary origin.