RickettsialesRANK: OrderTAXONOMY: cellular organisms -> Bacteria -> Proteobacteria -> Alphaproteobacteria -> Rickettsiales OVERVIEW: 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 mitochondriaand 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. The group includes all obligate endosymbiont bacteria. However, a number of species have been removed, such as Coxiella burnetii, the cause of Q fever.
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