Rickettsiaceae
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The Rickettsiaceae form a family within the Alphaproteobacteria and consist of the two genera Rickettsia and Orientia . All species are gram negative and require oxygen ( aerobic ). The cells of the different species are very small (0.3 to 0.5 × 0.8 to 2 μm) and rod-shaped or coccoid. They have a typical bacterial cell wall and do not have flagella.
Way of life
All species are obligate intracellular parasites, they can only survive within the host cells. They are the cause of numerous diseases in humans and animals. Arthropods (e.g. various ticks, fleas, mites, lice) are mainly used as vectors (carriers). A free cultivation on nutrient medium has so far not been successful; they are carried out within biological tissue, i. H. grown in eukaryotic cells.
Systematics and clinical classification
The Rickettsiaceae family is currently (January 2013) assigned to two genera, Rickettsia and Orientia .
From a medical point of view, the Rickettsiaceae are divided into three groups:
- The tick bite group (English: Spotted Fever Group): u. a. Rickettsia rickettsii ( Rocky Mountains spotted fever ) and Rickettsia conorii ( Boutonneuse fever )
- The typhus group: u. a. Rickettsia typhi (murine spotted fever)
- The Tsutsugamushi fever group (Scrub Typhus Group): This group consists of only one species, Orientia tsutsugamushi, the causative agent of Tsutsugamushi fever (English: Scrub typhus).
Changes to the system
It should be noted that the bacterial system is constantly in flux. So you can find several variants of the system of this family. The genus Wolbachia originally assigned to this family (see below) can be found in the Anaplasmataceae family or in the tribe Wolbachieae, which is still assigned to the Rickettsiaceae family.
The species originally called Rickettsia tsutsugamushi was separated from the genus Rickettsia and placed in its own genus Orientia . The often fatal tsutsugamushi fever (English: scrub typhus) occurs frequently in Asia and Australia. Mites of the genus Neotrombicula (Syn .: Trombicula ) serve as carriers .
In the past, Rickettsiaceae was divided into three tribes:
- Tribe Rickettsieae with the genera: Rickettsia , Rochalimaea and Coxiella
- Tribus Ehrlicheae with the genera: Ehrlichia , Cowdria and Neorickettsia
- Tribe Wolbachieae with the genera: Wolbachia , Symbiotes and Rickettsiella
The genera Ehrlicheae and the genus Wolbachia were included in the Anaplasmataceae family . Coxiella and Rickettsiella have been completely rearranged and placed in the family Coxiellaceae within the class Gammaproteobacteria . The species of Rochalimaea are now assigned to the genus Bartonella ( Bartonellaceae ).
In the past, all intracellular bacteria were assigned to the Rickettsiaceae (Rickettsiae). However, based on 16S-RNA analyzes, this systematic classification became untenable.
Endosymbiotic Theory
The species Rickettsia prowazekii is of particular interest in the endosymbiotic theory with regard to the mitochondria . The genome of Rickettsia prowazekii has been completely sequenced and shows very strong similarities with the mitochondrial DNA . However, it is unclear whether the original endosymbiont actually descended from the rickettsiae. The genome of Rickettsia prowazekii, like the genome found in the mitochondria, is very small. Both have presumably shrunk in the billions of years of evolution, whereby a strong similarity of the gene structure does not allow a clear statement.
swell
- ↑ Here after Euzéby: List of Prokaryotic Names with Standing in Nomenclature (LPSN) ( Memento of the original of April 27, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ According to: National Center for Biotechnology Information (NCBI) as of January 2012
- ↑ JP Euzéby: Dictionnaire de Bactériologie Vétérinaire ( Memento of the original of September 10, 2011 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
literature
- Martin Dworkin, Stanley Falkow, Eugene Rosenberg, Karl-Heinz Schleifer, Erko Stackebrandt (Eds.) The Prokaryotes, A Handbook of the Biology of Bacteria . 7 volumes, 3rd edition, Springer-Verlag, New York et al. O., 2006, ISBN 0-387-30740-0 . Vol. 5: Proteobacteria: Alpha and Beta Subclasses ISBN 0-387-25495-1
