Rickettsiales

Taxobox
color = lightgrey
name = Rickettsias
regnum = Bacteria
phylum = Proteobacteria
classis = Alpha Proteobacteria
ordo = Rickettsiales
ordo_authority = Gieszczkiewicz, 1939
subdivision_ranks = Families
subdivision =
Rickettsiaceae
Anaplasmataceaecite book
last = Garrity
first = George
title = Bergey's Manual of Systematic Bacteriology
publisher = Springer
year = 2005
isbn = 0-387-24145-0 ]
HolosporaceaeThe 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.

References