Rickettsiales
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Rickettsiales
(ri′ket·sē′ā·lēz)
(microbiology) An order of prokaryotic microorganisms; gram-negative, obligate, intracellular animal parasites (may be grown in tissue cultures); many cause disease in humans and animals.
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Rickettsiales
IN BRIEF: n. - Pleomorphic Gram-negative microorganisms.
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Saunders Veterinary Dictionary:
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Rickettsiales
An order of bacteria containing the families Rickettsiaceae and Anaplasmataceae. Small, obligately intracellular, gram-negative coccobacillary bacteria parasitizing host cells as a source of ATP. They are found in wild mammals, ticks, lice and trematodes and are transmitted by bites of arachnid or insect bites or by ingestion of trematodes. Generally replicate within erythrocytes, leukocytes or endothelial cells.
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Rickettsiales
| Rickettsias | |
|---|---|
 |
|
| Rickettsia rickettsii | |
| Scientific classification | |
| Kingdom: | Bacteria |
| Phylum: | Proteobacteria |
| Class: | Alphaproteobacteria |
| Order: | Rickettsiales Gieszczkiewicz, 1939 |
| Families | |
The Rickettsiales, also called rickettsias, are an order of small proteobacteria. Most of those described survive only as endosymbionts of other cells. Some are notable pathogens, including Rickettsia, which causes a variety of diseases in humans. On the other end of the scale, genetic studies support the endosymbiotic theory according to which mitochondria and related organelles developed from members of this group. Some have also speculated that viruses might have developed from them, or from organisms like them.
The Rickettsiales are among the most mysterious groups of Proteobacteria, owing largely to difficulties in cultivating them. Originally the group included all obligate endosymbiont bacteria. However, a number of species have been removed, such as Coxiella burnetii, the cause of Q fever. Environmental samples have found a variety of genes that originate from this group, pointing to a number of free-living planktonic species. These include SAR11, later cultivated as Pelagibacter ubique, one of the most common bacteria in the world. As of 2005, the exact composition and classification is far from settled.
| Phylogeny of Rickettsiales | |||||||||||||||||||||||||||||||||||||||||||||
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| Robust phylogeny of Rickettsiales from Williams et al. (2007)[2] |
References
- ^ Garrity, George (2005). Bergey's Manual of Systematic Bacteriology. Springer. ISBN 0-387-24145-0.
- ^ 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. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1913456.
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Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved.
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