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Evolution and diversity of Rickettsia bacteria.

Weinert LA, Werren JH, Aebi A, Stone GN, Jiggins FM - BMC Biol. (2009)

Bottom Line: All known vertebrate-associated Rickettsia are vectored by arthropods as part of their life-cycle, and many other Rickettsia are found exclusively in arthropods with no known secondary host.Rickettsia do not co-speciate with their hosts but host shifts most often occur between related arthropods.Recombination throughout the genus is generally uncommon, although there is evidence of horizontal gene transfer.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, EH9 3JT, UK. lucy.weinert@ed.ac.uk

ABSTRACT

Background: Rickettsia are intracellular symbionts of eukaryotes that are best known for infecting and causing serious diseases in humans and other mammals. All known vertebrate-associated Rickettsia are vectored by arthropods as part of their life-cycle, and many other Rickettsia are found exclusively in arthropods with no known secondary host. However, little is known about the biology of these latter strains. Here, we have identified 20 new strains of Rickettsia from arthropods, and constructed a multi-gene phylogeny of the entire genus which includes these new strains.

Results: We show that Rickettsia are primarily arthropod-associated bacteria, and identify several novel groups within the genus. Rickettsia do not co-speciate with their hosts but host shifts most often occur between related arthropods. Rickettsia have evolved adaptations including transmission through vertebrates and killing males in some arthropod hosts. We uncovered one case of horizontal gene transfer among Rickettsia, where a strain is a chimera from two distantly related groups, but multi-gene analysis indicates that different parts of the genome tend to share the same phylogeny.

Conclusion: Approximately 150 million years ago, Rickettsia split into two main clades, one of which primarily infects arthropods, and the other infects a diverse range of protists, other eukaryotes and arthropods. There was then a rapid radiation about 50 million years ago, which coincided with the evolution of life history adaptations in a few branches of the phylogeny. Even though Rickettsia are thought to be primarily transmitted vertically, host associations are short lived with frequent switching to new host lineages. Recombination throughout the genus is generally uncommon, although there is evidence of horizontal gene transfer. A better understanding of the evolution of Rickettsia will help in the future to elucidate the mechanisms of pathogenicity, transmission and virulence.

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Related in: MedlinePlus

Relationships and approximate dates of divergence of the major clades within the order Rickettsiales. The 16S rDNA phylogeny was reconstructed using one member of each of the groups shown with a molecular clock enforced (enforcing the clock did not reduce the likelihood of the tree: likelihood ratio test lnL = 13.84, df = 12 p = 0.311).
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Figure 2: Relationships and approximate dates of divergence of the major clades within the order Rickettsiales. The 16S rDNA phylogeny was reconstructed using one member of each of the groups shown with a molecular clock enforced (enforcing the clock did not reduce the likelihood of the tree: likelihood ratio test lnL = 13.84, df = 12 p = 0.311).

Mentions: Together, these phylogenetic analyses reveal five distinct and well-supported major clades of Rickettsia (Figure 1), one (designated the hydra group) containing protist-associated Rickettsia and a number with unknown host associations from sequences amplified from environmental samples, a second clade (torix) containing Rickettsia from amoeba, leeches and arthropods, a third (rhizobius) contains three beetle Rickettsia, a fourth (melloidae) containing a single beetle Rickettsia, a fifth (bellii) containing 11 strains of arthropod Rickettsia and a sixth clade of diverse bacteria containing both arthropod and vertebrate Rickettsia. This final clade can be further subdivided into the following groups: onychiurus, adalia, canadensis, spotted fever group, typhus group and transitional group, although bootstrap support for some of these groupings is less strong (all groups are also summarized in Figure 2).


Evolution and diversity of Rickettsia bacteria.

Weinert LA, Werren JH, Aebi A, Stone GN, Jiggins FM - BMC Biol. (2009)

Relationships and approximate dates of divergence of the major clades within the order Rickettsiales. The 16S rDNA phylogeny was reconstructed using one member of each of the groups shown with a molecular clock enforced (enforcing the clock did not reduce the likelihood of the tree: likelihood ratio test lnL = 13.84, df = 12 p = 0.311).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2662801&req=5

Figure 2: Relationships and approximate dates of divergence of the major clades within the order Rickettsiales. The 16S rDNA phylogeny was reconstructed using one member of each of the groups shown with a molecular clock enforced (enforcing the clock did not reduce the likelihood of the tree: likelihood ratio test lnL = 13.84, df = 12 p = 0.311).
Mentions: Together, these phylogenetic analyses reveal five distinct and well-supported major clades of Rickettsia (Figure 1), one (designated the hydra group) containing protist-associated Rickettsia and a number with unknown host associations from sequences amplified from environmental samples, a second clade (torix) containing Rickettsia from amoeba, leeches and arthropods, a third (rhizobius) contains three beetle Rickettsia, a fourth (melloidae) containing a single beetle Rickettsia, a fifth (bellii) containing 11 strains of arthropod Rickettsia and a sixth clade of diverse bacteria containing both arthropod and vertebrate Rickettsia. This final clade can be further subdivided into the following groups: onychiurus, adalia, canadensis, spotted fever group, typhus group and transitional group, although bootstrap support for some of these groupings is less strong (all groups are also summarized in Figure 2).

Bottom Line: All known vertebrate-associated Rickettsia are vectored by arthropods as part of their life-cycle, and many other Rickettsia are found exclusively in arthropods with no known secondary host.Rickettsia do not co-speciate with their hosts but host shifts most often occur between related arthropods.Recombination throughout the genus is generally uncommon, although there is evidence of horizontal gene transfer.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, EH9 3JT, UK. lucy.weinert@ed.ac.uk

ABSTRACT

Background: Rickettsia are intracellular symbionts of eukaryotes that are best known for infecting and causing serious diseases in humans and other mammals. All known vertebrate-associated Rickettsia are vectored by arthropods as part of their life-cycle, and many other Rickettsia are found exclusively in arthropods with no known secondary host. However, little is known about the biology of these latter strains. Here, we have identified 20 new strains of Rickettsia from arthropods, and constructed a multi-gene phylogeny of the entire genus which includes these new strains.

Results: We show that Rickettsia are primarily arthropod-associated bacteria, and identify several novel groups within the genus. Rickettsia do not co-speciate with their hosts but host shifts most often occur between related arthropods. Rickettsia have evolved adaptations including transmission through vertebrates and killing males in some arthropod hosts. We uncovered one case of horizontal gene transfer among Rickettsia, where a strain is a chimera from two distantly related groups, but multi-gene analysis indicates that different parts of the genome tend to share the same phylogeny.

Conclusion: Approximately 150 million years ago, Rickettsia split into two main clades, one of which primarily infects arthropods, and the other infects a diverse range of protists, other eukaryotes and arthropods. There was then a rapid radiation about 50 million years ago, which coincided with the evolution of life history adaptations in a few branches of the phylogeny. Even though Rickettsia are thought to be primarily transmitted vertically, host associations are short lived with frequent switching to new host lineages. Recombination throughout the genus is generally uncommon, although there is evidence of horizontal gene transfer. A better understanding of the evolution of Rickettsia will help in the future to elucidate the mechanisms of pathogenicity, transmission and virulence.

Show MeSH
Related in: MedlinePlus