- International Journal of Systematic and Evolutionary Microbiology
- Volume 44, Issue 4
f Ancestral Divergence of Rickettsia bellii from the Spotted Fever and Typhus Groups of Rickettsia and Antiquity of the Genus Rickettsia
- Authors: DIANE R. STOTHARD, JONATHAN B. CLARK†, PAUL A. FUERST*
- * Corresponding author. Mailing address: Department of Molecular Genetics, The Ohio State University, 484 W. 12th Avenue, Columbus, OH 43210-1292. Phone: (614) 292-6403. Fax: (614) 292-4466. Electronic mail address: email@example.com.
- Int J Syst Evol Microbiol, October 1994 44: 798-804, doi: 10.1099/00207713-44-4-798
- Subject: Original Papers Relating To Systematic Bacteriology
- Published Online:
The eubacterial genus Rickettsia belongs to the α subgroup of the phylum Proteobacteria. This genus is usually divided into three biotypes on the basis of vector host and antigenic cross-reactivity characteristics. However, the species Rickettsia bellii does not fit into this classification scheme; this organism has characteristics common to both the spotted fever group and the typhus group biotypes and also exhibits some unique features. Sequences of the 16S rRNA and 23S rRNA genes from Rickettsia rickettsii (spotted fever group), Rickettsia prowazekii (typhus group), and R. bellii were studied to determine the position of R. bellii in the rickettsial classification scheme. The 23S rRNA gene sequences described in this paper are the first 23S rRNA sequences reported for any member of the Rickettsiaceae. The 23S rRNA gene contains substantially more phylogenetic information than is contained in the 16S rRNA sequences, and the 23S rRNA gene sequence has diverged about 1.9 times faster in the three Rickettsia species which we studied. Taken together, the molecular data obtained from the two genes indicate that R. bellii is not a member of either the spotted fever group or the typhus group; rather, this organism appears to be the product of a divergence which predates the separation of the genus into the spotted fever group and the typhus group. Consequently, different combinations of the ancestral characteristics retained by R. bellii have been retained in the more derived lineages of the genus. A comparison of the 16S rRNA and 23S rRNA gene sequences of Rickettsia strains with other proteobacterial sequences confirmed that the genus Rickettsia is a unique deeply branching member of the α subgroup of the Proteobacteria and that the Rickettsia species form a monophyletic cluster. While divergence of the contemporary members of the genus Rickettsia occurred recently, the unique evolutionary line represented by this genus appears to be very old.
Present address: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721.
Copyright © 1994 International Union of Microbiological Societies | Published by the Microbiology Society
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