Rickettsiales

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Rickettsias
Rickettsia rickettsii.jpg
Rickettsia rickettsii
Scientific classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Alphaproteobacteria
Order: Rickettsiales
Gieszczkiewicz, 1939
Families

Rickettsiaceae
Anaplasmataceae [1] Holosporaceae

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
Other alphaproteobacteria

Rhodospirillales, Sphingomonadales, Rhodobacteraceae, Rhizobiales, etc.


Rickettsiales
SAR11 clade

Pelagibacter ubique




Mitochondria



Anaplasmataceae



Ehrlichia



Anaplasma




Wolbachia




Neorickettsia



Rickettsiaceae

Rickettsia






Robust phylogeny of Rickettsiales from Williams et al. (2007)[2]

References[edit]

  1. ^ Garrity, George (2005). Bergey's Manual of Systematic Bacteriology. Springer. ISBN 0-387-24145-0. 
  2. ^ 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