text: Rickettsia rickettsii is a Gram-negative, intracellular, coccobacillus bacterium that was first discovered in 1902. Having a reduced genome, the bacterium harvests nutrients from its host cell to carry out respiration, making it an organoheterotroph. Maintenance of its genome is carried out through vertical gene transfer where specialization of the bacterium allows it to shuttle host sugars directly into its TCA cycle.
  Other characteristics of the bacteria include membrane proteins that are useful in the identification of R. rickettsii strains and useful in the targeting of antibiotics. A capsule encircling the bacterium allows for attachment to host cells and additionally acts as a defense mechanism for resisting phagocytosis. Varying strains of R. rickettsii have different genotypes and phenotypes that alter the pathogenicity, virulence, and appearance of the bacteria.