Phylogenetic diversity of the Rickettsiae

Abstract

Small subunit rRNA sequences have been determined for representative strains of six species of the family Rickettsiaceae: Rickettsia rickettsii, Rickettsia prowazekii, Rickettsia typhi, Coxiella burnetii, Ehrlichia risticii, and Wolbachia persica. The relationships among these sequences and those of other eubacteria show that all members of the family Rickettsiaceae belong to the so-called purple bacterial phylum. The three representatives of the genus Rickettsia form a tight monophyletic cluster within the a subdivision of the purple bacteria. E. risticii also belongs to the a subdivision and shows a distant yet specific relationship to the genus Rickettsia. However, the family as a whole is not monophyletic, in that C. burnetii and W. persica are members of the -y subdivision. The former appears to show a specific, but rather distant, relationship to the genus Legionella.The order Rickettsiales (32) comprises a collection of procaryotes that share the property of intimate association with eucaryotic cells. The relationship in most cases is obligate intracellular parasitism, although a few of these bacteria have been grown in complex host-cell-free culture media. Although this order contains notorious pathogens of humans and animals, some of these bacteria cause no obvious damage to their host, and the relationship can be regarded as commensal. The Rickettsiales are clearly separate from the Chlamydiales (17), a narrowly defined group of energy-parasitizing, obligately intracellular bacteria. Certain fastidious parasites of plant vascular tissues and arthropods, sometimes referred to as rickettsialike (5), are not included in either category. Also, the highly heterogeneous group of bacteria that have established an endosymbiotic relationship with their hosts and for the most part have not been cultivated, including the hydrothermal-vent-associated symbionts (3,4,21), are viewed as distinct from the Rickettsiales (32) in the latest edition of Bergey's Manlual of Systematic Bacteriology.The order Rickettsiales contains three families: Rickettsiaceae, Bartonellaceae, and Anaplasmataceae. Our present study is confined to the family Rickettsiaceae, which is divided into three tribes: Rickettsieae, Ehrlichieae, and Wolbachieae (32). In the family Rickettsiaceae, rigorous criteria of classical taxonomy have been applied to the definition of most species and, in some but not in all cases, the genera. For example, good evidence was obtained by phenotypic analysis, DNA base ratio determinations, and DNA-DNA hybridization studies that in the genus Rickettsia, members of the typhus and spotted fever groups are related (32). However, the degree of relatedness of these microorganisms to the scrub typhus rickettsia, Rickettsia tsutsugamushi, remains unknown. Similarly, phenotypic analysis links the monocytic erhlichiae (Ehrlichia canis, Ehrlichia sennetsu, and Ehrlichia risticii) to each other (10,22,23), but their relationships to the granulocytic ehrlicheae * Corresponding author. t Present address: Gene-Trak Systems,

Ancestral Divergence of Rickettsia bellii from the Spotted Fever and Typhus Groups of Rickettsia and Antiquity of the Genus Rickettsia

“…Restriction digests obtained by using HindIII and the genomic DNAs of 12 Rickettsia species, including R. bellii, R. prowazekii, and R. rickettsii, produced single bands, which was consistent with the presence of a single copy of the 16s rRNA gene in all taxa, when they were probed with the 16s ribosomal DNA clone from Rochalimaea quintana (pMD24). No Hind111 site was identified in the previously described sequences of R. rickettsii, R. prowazekii, and R. typhi (34). Single-band patterns consistent with the hypothesis that there are single copies of the 16s rRNA gene in R. bellii, R. prowazekii, and the SFG species Rickettsia montana were aIso obtained when genomic DNA restricted by either SphI or EcoRI was probed by using labeled R. bellii 16s rRNA.…”

“…In addition, the complete or nearly complete 16s rRNA gene sequences of several other Rickettsia species or Rickettsia-like organisms have been determined recently (30a, 37). However, even when SFG species are compared with TG species, the numbers of sequence differences found in the 16s rRNA gene in the genus Rickettsia are quite small (34). Therefore, we also obtained data for the large-subunit rRNA gene to help clarify the ambiguous evolutionary relationships between R. bellii and the SFG and TG species.…”

“…Nearly complete sequences of the 16s rRNA genes of R. rickettsii and R. prowazekii have been described previously (34). In addition, the complete or nearly complete 16s rRNA gene sequences of several other Rickettsia species or Rickettsia-like organisms have been determined recently (30a, 37).…”

“…The obligately intracellular lifestyle and fastidious nature of these organisms have made them difficult to study. A number of genotypic and phenotypic characteristics indicate that the Rickettsia species are closely related, and this genus is now recognized as the sole member of a branch of the cx subgroup Proteobacteriu (8) on the basis of 16s rRNA cataloging and partial 16s rRNA gene sequence data (34).…”

The RecA protein as a model molecule for molecular systematic studies of bacteria: Comparison of trees of RecAs and 16S rRNAs from the same species

“…2b, Table 2). Analysis of other SS-rRNA sequences suggests that the position of the Legionellaceae in the γ subgroup is robust (Fry et al 1991;Weisburg et al 1989a). Similarly, the exact position of the N. gonorrhoeae RecA is ambiguous, yet the N. gonorrhoeae SS-rRNA groups consistently with the β clade.…”