A phylogenetic analysis of the cytochrome b and cytochrome c oxidase I genes supports an origin of mitochondria from within the Rickettsiaceae.

We have cloned and sequenced the genes encoding cytochrome b (cob) and cytochrome c oxidase subunit I (cox1) from Rickettsia prowazekii, a member of the alpha-proteobacteria. The phylogenetic analysis supports the hypothesis that mitochondria are derived from the alpha-proteobacteria and more specifically from within the Rickettsiaceae. We have estimated that the common ancestor of mitochondria and Rickettsiaceae dates back to more than 1500 million years ago.