Rickettsiaceae

The Rickettsiaceae are a family of bacteria. The genus Rickettsia is the most prominent genus within the family. The bacteria that eventually formed the mitochondrion (an organelle in eukaryotic cells) is believed to have originated from this family. 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.

Rickettsiaceae
Rickettsia rickettsii (red dots) in the cell of a deer tick
Scientific classification
Domain:	Bacteria
Phylum:	Pseudomonadota
Class:	Alphaproteobacteria
Order:	Rickettsiales
Family:	Rickettsiaceae Pinkerton 1936 (Approved Lists 1980)
Tribes and genera
"Candidatus Arcanobacter" Martijn et al. 2015 "Candidatus Cryptoprodota" corrig. Ferrantini et al. 2009 "Dermacentroxenus" Wolbach 1919 "Candidatus Gigarickettsia" Vannini et al. 2014[1]* "Candidatus Hemipteriphilus" Bing et al. 2013 "Candidatus Megaira" Schrallhammer et al. 2013 Occidentia Mediannikov et al. 2017 Orientia Tamura et al. 1995 "Candidatus Phycorickettsia" Yurchenko et al. 2018 Rickettsia da Rocha-Lima 1916 (Approved Lists 1980) "Candidatus Sarmatiella" Castelli et al. 2021 "Candidatus Spectririckettsia" Castelli et al. 2019 "Candidatus Tisiphia" Davison et al. 2022 "Candidatus Trichorickettsia" Vannini et al. 2014[1] "Candidatus Xenohaliotis" Friedman et al. 2000

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.^[2] 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.^[3]

Schematic ribosomal RNA phylogeny of Alphaproteobacteria

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

The cladogram of Rickettsidae has been inferred by Ferla et al. [4] from the comparison of 16S + 23S ribosomal RNA sequences.

References

1. Vannini C, Boscaro V, Ferrantini F, Benken KA, Mironov TI, Schweikert M, Görtz HD, Fokin SI, Sabaneyeva EV, Petroni G (2014). "Flagellar Movement in Two Bacteria of the Family Rickettsiaceae: A Re-Evaluation of Motility in an Evolutionary Perspective". PLOS ONE. 9 (2): e87718. Bibcode:2014PLoSO...987718V. doi:10.1371/journal.pone.0087718. PMC 3914857. PMID 24505307.
2. 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.
3. 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.
4. Ferla MP, Thrash JC, Giovannoni SJ, Patrick WM (2013). "New rRNA gene-based phylogenies of the Alphaproteobacteria provide perspective on major groups, mitochondrial ancestry and phylogenetic instability". PLOS ONE. 8 (12): e83383. Bibcode:2013PLoSO...883383F. doi:10.1371/journal.pone.0083383. PMC 3859672. PMID 24349502.