Rickettsiae are obligate intracellular bacteria with metabolically-reduced genomes. Curiously, only some rickettsiae (i.e. Typhus and Transitional Group pathogens) synthesize large cytoplasmic granules. In unrelated Proteobacteria, similar granules contain polyhydroxybutyrate (PHB) as an energy reserve in response to oxidative stress, heavy-metal stress, or excess carbon. PHB chains are degraded to yield substrates for generating cellular energy. It is hypothesized that rickettsiae have conserved the genes for PHB synthesis and utilization. In this study, genes for utilizing acetate (a precursor for PHB biosynthesis) were used to construct a theoretical pathway for PHB synthesis. Phylogenomic analysis was conducted and revealed only Typhus and Transitional Group rickettsiae have conserved the ability to synthesize PHB. Finally, phylogeny estimation of these genes indicates their vertical inheritance from a common Rickettsia ancestor, revealing all Spotted Fever Group rickettsiae have lost the ability to utilize acetate. Implications for a role of PHBs in extracellular survival for these rickettsial species are discussed.