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The emerging diversity of Rickettsia - PubMed

  • ️Sun Jan 01 2006

Review

The emerging diversity of Rickettsia

Steve J Perlman et al. Proc Biol Sci. 2006.

Abstract

The best-known members of the bacterial genus Rickettsia are associates of blood-feeding arthropods that are pathogenic when transmitted to vertebrates. These species include the agents of acute human disease such as typhus and Rocky Mountain spotted fever. However, many other Rickettsia have been uncovered in recent surveys of bacteria associated with arthropods and other invertebrates; the hosts of these bacteria have no relationship with vertebrates. It is therefore perhaps more appropriate to consider Rickettsia as symbionts that are transmitted vertically in invertebrates, and secondarily as pathogens of vertebrates. In this review, we highlight the emerging diversity of Rickettsia species that are not associated with vertebrate pathogenicity. Phylogenetic analysis suggests multiple transitions between symbionts that are transmitted strictly vertically and those that exhibit mixed (horizontal and vertical) transmission. Rickettsia may thus be an excellent model system in which to study the evolution of transmission pathways. We also focus on the emergence of Rickettsia as a diverse reproductive manipulator of arthropods, similar to the closely related Wolbachia, including strains associated with male-killing, parthenogenesis, and effects on fertility. We emphasize some outstanding questions and potential research directions, and suggest ways in which the study of non-pathogenic Rickettsia can advance our understanding of their disease-causing relatives.

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Figures

Figure 1
Figure 1

Phylogenetic tree of Rickettsia 16S rDNA sequences, using a Kimura 3 parameter distance model of evolution; topology does not differ significantly from maximum parsimony and maximum-likelihood trees. This tree is rooted with 16S sequences from a Diophrys ciliate symbiont and two environmental samples. Statistical support for nodes was determined by conducting 500 parsimony and distance bootstraps. Bootstrap support symbols: plus, a node that has greater than 50% bootstrap support; filled circle, a node that has greater than 70% bootstrap support and asterisk, a node that has greater than 90% bootstrap support, with the first symbol referring to parsimony bootstrap and the second to distance bootstrap. Rickettsia strain biology: ‘A’ refers to arthropod symbionts, ‘P’ refers to symbionts associated with vertebrate pathogenicity, ‘R’ refers to symbionts associated with reproductive manipulation.

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