The Phylogeny ofRickettsiaUsing Different Evolutionary Signatures: How Tree-Like is Bacterial Evolution?

Abstract

Rickettsia is a genus of intracellular bacteria whose hosts and transmission strategies are both impressively diverse, and this is reflected in a highly dynamic genome. Some previous studies have described the evolutionary history of Rickettsia as non-tree-like, due to incongruity between phylogenetic reconstructions using different portions of the genome. Here, we reconstruct the Rickettsia phylogeny using whole-genome data, including two new genomes from previously unsampled host groups. We find that a single topology, which is supported by multiple sources of phylogenetic signal, well describes the evolutionary history of the core genome. We do observe extensive incongruence between individual gene trees, but analyses of simulations over a single topology and interspersed partitions of sites show that this is more plausibly attributed to systematic error than to horizontal gene transfer. Some conflicting placements also result from phylogenetic analyses of accessory genome content (i.e., gene presence/absence), but we argue that these are also due to systematic error, stemming from convergent genome reduction, which cannot be accommodated by existing phylogenetic methods. Our results show that, even within a single genus, tests for gene exchange based on phylogenetic incongruence may be susceptible to false positives.

Torix group Rickettsia are widespread in Culicoides biting midges (Diptera: Ceratopogonidae), reach high frequency and carry unique genomic features

“…Support values are based on 100 rapid bootstrap replicates. Major Rickettsia groups have been collapsed for visualisation purposes and names are according to (Murray et al, 2016). Numbers in parenthesis represent the number of genomes used for the analysis (Table S2).…”

Molecular detection of Rickettsia species in ticks collected from the southwestern provinces of the Republic of Korea

“…Rickettsia conorii , R. rickettsii and R. japonica , the causative agents of Mediterranean, Rocky Mountain, and Japanese spotted fever, respectively, that are transmitted by ixodid ticks); (ii) the typhus group (TGR) (e.g. R. typhi , the causative agent of murine typhus transmitted by fleas, and R. prowazekii , the causative agent of epidemic typhus transmitted by the body louse); (iii) the transitional group (TRGR) transmitted by fleas, mites and ticks; (iv) the R. bellii group (ticks); (v) the R. canadensis group; (vi) the Helvetica group; (vii) the Scapularis group; (viii) the Adalia group; and (ix) the Hydra group [1–4]. …”

Serological survey of Rickettsia in equids from Vale do Paraíba, São Paulo, Brazil, and their tick identification and molecular investigation of Rickettsia

“…R. bellii has been reported as the species of Rickettsia most commonly infecting ticks in Brazil (Krawczak et al, 2018;Labruna et al, 2011). This bacteria belongs to a rickettsial basal group that includes a variety of closely related agents infecting leeches, insects, protozoa, or even plants (Murray et al, 2016;Weinert et al, 2009), making it possible that these other organisms could be related to the seropositivity of R. bellii in the present study, a condition still not investigated. Medeiros et al (2013) demonstrated the occurrence of cross-reaction between different species of Rickettsia in horses.…”