Rickettsiaceae

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

The Rickettsiaceae are a family of bacteria. The genus Rickettsia is the most prominent genus within the family. From this family, the bacteria that eventually formed the mitochondrion (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 lifecycle 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, thus is adapted to obligate intracellular infection. Rickettsia rickettsii is considered the prototypical infectious organism in the group.

Genomics

Comparative genomic analysis has identified three 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 four-amino-acid insert in transcription repair coupling factor Mfd, a 10-amino-acid insert in ribosomal protein L19, one-amino-acid inserts each in the FtsZ protein and the major sigma factor 70, and a one-amino-acid deletion in exonuclease VII protein that are specific for the Rickettsiaceae species have been identified.^[2]

Phylogeny of Rickettsiales

Magnetococcidae Magnetococcales Magnetococcaceae Magnetococcus marinus Caulobacteridae Rhodospirillales, Sphingomonadales, Rhodobacteraceae, Rhizobiales, etc. Holosporales Rickettsidae Pelagibacterales Pelagibacteraceae Pelagibacter subgroups Ib, II, IIIa, IIIb, IV and V Proto-mitochondria Anaplasmataceae Ehrlichia Anaplasma Wolbachia Neorickettsia Midichloriaceae Midichloria Rickettsiaceae Rickettsia

Robust 16S + 23S phylogeny of Rickettsidae from Ferla et al. (2013)[3]

References

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. Ferla, M. P.; Thrash, J. C.; Giovannoni, S. J.; Patrick, W. M. (2013). "New rRNA gene-based phylogenies of the Alphaproteobacteria provide perspective on major groups, mitochondrial ancestry and phylogenetic instability". PLoS ONE. 8 (12): e83383. doi:10.1371/journal.pone.0083383. PMC 3859672. PMID 24349502.