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Scientific classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Alphaproteobacteria
Order: Rickettsiales
Family: Rickettsiaceae
Pinkerton, 1936


The Rickettsiaceae are a family of bacteria. The genus Rickettsia is the most prominent genus within the family.

It is from this family that the bacteria that eventually formed the mitochondria (an organelle in Eukaryotic cells) is believed to have originated.

Most human pathogens in this family are in genus Rickettsia. They spend part of their life cycle in the bodies of arthropods such as ticks or lice, and are then transmitted to humans or other mammals by the bite of the arthropod.

It contains Gram-negative bacteria, very sensitive to environmental exposure, and thus adapted to obligate intracellular infection.

Rickettsia rickettsii is considered the prototypical infectious organism in the group.

Similar arthropod borne Rickettsial infections exist in other areas of the world.


Comparative genomic analysis has identified 3 proteins, RP030, RP187 and RP192, which are uniquely found in members of the family Rickettsiaceae and serve as molecular markers for this family.[1] In addition, conserved signature indels in a number of proteins including a 4 amino acid insert in transcription repair coupling factor Mfd, a 10 amino acid insert in ribosomal protein L19, 1 amino acid inserts each in the FtsZ protein and the major sigma factor 70, and a 1 amino acid deletion in exonuclease VII protein that are specific for the Rickettsiaceae species have been identified.[2]

Phylogeny of Rickettsiales
Other alphaproteobacteria

Rhodospirillales, Sphingomonadales, Rhodobacteraceae, Rhizobiales, etc.

SAR11 clade

Pelagibacter ubique









Robust phylogeny of Rickettsiales from Williams et al. (2007)[3]


  1. ^ Gupta, R. S. and Mok, A. (2007). Phylogenomics and signature proteins for the alpha Proteobacteria and its main groups. BMC Microbiology. 7:106. DOI:10.1186/1471-2180-7-106.
  2. ^ Gupta, R. S. (2005). Protein signatures distinctive of alpha proteobacteria and its subgroups and a model for alpha proteobacterial evolution. Critical Reviews in Microbiology. 3:101-135. DOI: 10.1080/10408410590922393.
  3. ^ Williams, K. P.; Sobral, B. W.; Dickerman, A. W. (2007). "A Robust Species Tree for the Alphaproteobacteria". Journal of Bacteriology 189 (13): 4578–4586. doi:10.1128/JB.00269-07. PMC 1913456. PMID 17483224.  edit