This group comprises arthropod-borne intracellular parasites of vertebrates, and in-cludes the causative agents of human diseases such as typhus and Rocky Mountainspotted fever. The bacteria are taken up by host phagocytic cells, where they multiplyand eventually cause lysis.
The Rickettsia are aerobic organotrophs, but some possess an unusual mode of en-ergy metabolism, only being able to oxidise intermediate metabolites such as glutamate and succinate, which they obtain from their host. Rickettsia and Coxiella, the two main genera, are not closely related phylogenetically and are placed in the Î±- and Î³ - Proteobacteria, respectively.
Representative genera: Rickettsia, Coxiella