Open Access

Evolution and diversity of Rickettsiabacteria

  • Lucy A Weinert1Email author,
  • John H Werren2,
  • Alexandre Aebi3,
  • Graham N Stone1 and
  • Francis M Jiggins1
BMC Biology20097:6

DOI: 10.1186/1741-7007-7-6

Received: 30 July 2008

Accepted: 02 February 2009

Published: 02 February 2009









Rickettsia bacteria are intracellular symbionts of eukaryotes. The genus is classified in the family Rickettsiaceae within the alpha-proteobacteria, and is closely related to the genera Erlichia and Wolbachia [1, 2]. Rickettsia are most noted for causing human diseases, including Rocky Mountain spotted fever and epidemic typhus, which has been a major source of mortality at times in human history [3]. However, 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 (for convenience, we will refer to the former as 'vertebrate Rickettsia' and the latter as 'arthropod Rickettsia'). In recent years, arthropod Rickettsia have been discovered in a diverse range of hosts, suggesting that they are more common than had been suspected [416]. Nevertheless, research effort has tended to concentrate on the medically important vertebrate Rickettsia, or on the more common arthropod endosymbionts, such as Wolbachia and Cardinium, and so we know little about the biology of arthropod Rickettsia. Even less is known about the closely related bacteria that have been recently discovered in organisms such as leeches and protists, and in metagenomic studies sequencing all DNA in an environmental sample [1725]. This neglect is unfortunate, because comparing the vertebrate pathogens with related species can help to elucidate the mechanisms of pathogenicity, transmission and virulence [26, 27]. However, this requires a robust phylogeny for the genus.

Historically, Rickettsia were classified into three major groups based on serological characteristics, namely the 'typhus group', 'spotted fever group' and 'scrub typhus group', although subsequent DNA sequencing led to the latter being reassigned to the related genus Orientia [28]. The relationship of species within the remaining two groups of Rickettsia has been the subject of intensive study over the last decade as progressively more informative genes have been sequenced [2932] culminating in a multi-genic approach [33]. As a result it has been suggested that the spotted fever group consists of two sister clades, one of which is now designated 'transitional' [34] (although see [35]). A fourth so-called 'ancestral' clade, including Rickettsia bellii and Rickettsia canadensis, is thought to be basal to the other groups and is largely non-pathogenic to vertebrates. However, the position of R. canadensis remains uncertain [33].




Strains identified and genes sequenced

Table 1

Rickettsia strains sequenced.

Rickettsia obtained from:

Host order

Host species

This study:


   Worldwide screen


Noctuidae (moth)



Chrysopidae (lacewing)



Elateridae (beetle)



Curculionidae (weevil)



Bombyliidae (bee fly)



Bombyliidae (bee fly)



Reduviidae (assassin bug)



Meloidae (blister beetle)



Cercopidae (spittlebug)

   Ladybird screen


Subcoccinella vigintiquattuorpunctata (24 spot ladybird)



Halyzia sedecimguttata (orange ladybird)



Calvia quattuordecimguttata (cream spot ladybird)



Coccidula rufa (ladybird)



Rhizobius chrysomeloides (ladybird)



Scymnus suturalis (ladybird)



Adalia bipunctata (2 spot ladybird) edinburgh



Adalia decempuntata (10 spot ladybird)

   Gall wasp screen


Pediobius rotundatus



Aulogymnus balani/skianeuros



Aulogymnus trilineatus

Previous studies:


   Jiggins and Tinsley [79]


Adalia bipunctata (2 spot ladybird) moscow



Adalia bipunctata (2 spot ladybird) cambridge



Adalia bipunctata (2 spot ladybird) ribe

   Chen et al. [14]


Acyrthosiphon pisum (pea aphid)

   Lawson et al. [7]


Brachys tessellatus (buprestid beetle)

Rickettsia phylogeny


Table 2

Likelihood values of SH tests.


Likelihood of tree topology



























Figure 1



Figure 2


Host shifts






Figure 3






The evolutionary history of Rickettsia

It is useful to view our results in the context of the evolution of the whole order Rickettsiales. To do this, we have used a molecular clock to date the divergence of different groups, and this is shown in Figure 2. The common ancestor was presumably free-living, as the earliest diverging genus of the order is Pelagibacter. Pelagibacter species account for 26% of the bacterial rDNA sequences from sea water [43] and have the smallest genomes of free-living bacteria. About 525–775 million years ago there was a transition to living within cells, followed by a split into endosymbionts of protists (Holospora) [44, 45] and a clade that primarily infects arthropods. Holospora species infect the nuclei of paramecium and are generally considered pathogenic to their hosts; for example, Holospora undulata can sterilise their hosts, reduce the rate of asexual division and increase host mortality [46]. The most parsimonious interpretation of the tree, therefore, is that the transition to infecting arthropods occurred approximately 425–525 million years ago in this lineage (Figure 2), which can be compared to the first appearance of most metazoan phyla in the Cambrian explosion (approximately 540 million years ago).

All other genera in the order Rickettsiales are associated with arthropods although many have other diverse hosts. The genus Midichloria has only been found in Ixodidae ticks, and resides inside mitochondria. Bacteria in the genus Neorickettsia are primarily associated with helminths, where they can be transmitted to vertebrates [47]. Wolbachia have been described in only arthropods and nematodes, and most are thought to be vertically transmitted (reviewed in [48]). Ehrlichia and Anaplasma are horizontally transmitted in arthropods and vertebrates [49, 50] and Orientia are vertically transmitted in mites and can be horizontally transferred to humans [51, 52].






The recent discovery of plasmids in the genus Rickettsia opens up the possibility that horizontal gene transfer may be common between strains [5659]. Furthermore, there have been reports of recombination between Rickettsia strains [60, 61]. This has important implications for the evolution of Rickettsia, as genes can sweep through different genetic backgrounds of bacterial strains, thereby potentially increasing the spread of genes altering bacterial pathogenicity. Recombination can also complicate the inference of relationships between strains, as recombination violates the assumption that a strain has one evolutionary history.



Transmission and population dynamics

It is clear from our data that Rickettsia are common and diverse bacteria. However, the basic biology of most of these strains is entirely unknown and it is therefore unclear how these have spread through populations. As Rickettsia are primarily intracellular, they cannot survive for long in the external environment (but see [63] for cell-free persistence of related Wolbachia). For this reason, they are most readily maintained either by vertical transmission (mother to offspring) in their arthropod hosts or, in the case of blood-sucking arthropods, by horizontal transmission through an infected vertebrate (one case is also known of transmission through a plant [10]). Because infectious transmission between arthropod hosts is thought to be rare, the general view is that exclusively arthropod Rickettsia are maintained within a host species primarily by transovarial transmission, and therefore must enhance the fitness of infected females [64]. Some Rickettsia raise infected female fitness in an indirect way by manipulating host reproduction towards infected daughters at the expense of sons, either by killing male offspring as embryos (male-killing) or by inducing parthenogenesis [13, 65]. The closely related bacterium O. tsutsugamushi also causes a female biased sex ratio in its mite host [66]. Theoretically, arthropod Rickettsia could also be maintained by directly providing a fitness benefit to infected females as shown for other bacterial groups [6771], eg by providing essential nutrients or protection from other infective agents. Although, Rickettsia are required for egg production in the booklouse Liposcelis bostrychophila, and are therefore obligatory, in most cases where the arthropod relationship has been studied in depth, Rickettsia are pathogenic [8, 7274] or have no observable effect [75, 76], making a mutualistic role for Rickettsia in those hosts unlikely.

For those Rickettsia that are vertebrate pathogens but vectored by arthropods, the effects of the bacteria on their arthropod hosts are generally poorly understood [72].Rickettsia prowazekii is clearly pathogenic to infected lice, and transmission through humans is essential to the maintenance of the bacteria in arthropod populations. In every other case, human infections are accidental, but transmission through other vertebrates may allow the bacteria to persist in populations. Many of the bacteria that can infect vertebrates are also transmitted vertically by the arthropod host [76]. In these cases, even very occasional horizontal transmission through the vertebrate host can enhance the maintenance of bacteria in arthropod populations.






Bacterial strains

We obtained most of the Rickettsia strains we sequenced from three PCR screens of insects collected in the wild (Table 1). These used primers that amplify the 16S rDNA of Rickettsia [15]. The first screen tested 2149 ladybirds from 21 different species collected from the UK, Germany, Spain and New Zealand for the presence of Rickettsia [6]. We sequenced a Rickettsia from a single individual from each of the eight species shown to be infected. The second screen tested 1458 individuals of Hymenoptera associated with galls induced by oak gall wasps (Hymenoptera: Cynipidae, Cynipini; [78]), comprising nine species of oak gall wasp, 26 species of associated chalcid parasitoid, and ten species of oak gall wasp inquiline (Hymenoptera: Cynipidae, Synergini) (A Aebi and G Stone, unpublished data). We sequenced a Rickettsia from single individuals from three of the four species that were infected. The third study screened 847 individuals, each of which was a different species of arthropod from the classes Arachnida, Entognatha, Malacostraca and Insecta. The individuals from Arachinida comprised six of the order Araneae and one Holothyrida. The five Entognatha were all Collembola and the individual from Malacostraca was from the order Isopoda. The individuals from the Insecta comprised 240 of the order Hymenoptera, 218 Diptera, 206 Coleoptera, 86 Hemiptera, 28 Lepidoptera, nine Orthoptera, nine Thysanoptera, eight Odonata, eight Heteroptera, five Homoptera, five Blattodea, four Neuroptera, three Dermaptera, and one individual each of Mantodea, Pscoptera, Siphonaptera, Strepsiptera, and Trichoptera (L Weinert and J Werren, unpublished data). The insects were collected from worldwide locations. All nine Rickettsia isolates from this screen were sequenced. More detailed information on infected and uninfected species from unpublished data can be found in the supplementary information (Additional file 4, The distribution of Rickettsia among arthropods). We also included a Rickettsia from the pea aphid Acyrthosiphon pisum [8], a male-killing Rickettsia from the buprestid beetle Brachys tessellatus [7] and three Rickettsia strains from the ladybird beetle A. bipunctata, each of which has been shown to be genetically distinct [73, 79].

PCR and sequencing

To obtain estimates of phylogeny from different portions of the genome, we sequenced four different genes, which are at least 200 kbps apart in the R. bellii genome. Of the genes used in a previous study to produce a multi-gene vertebrate Rickettsia phylogeny [33], we sequenced 16S rDNA and atpA, which are the only ones that have homologues conserved enough to produce alignments in O. tsutsugamushi. We also targeted the coxA gene as it is used in Wolbachia multilocus strain type analysis [80] and is found in Orientia and all Rickettsia genomes except for R. typhi. We also used the gltA gene, which is commonly sequenced from Rickettsia strains [30] and, although it is absent from the O. tsutsugamushi genome, it is conserved throughout all other Rickettsiales [38]. This provides four genes for our multi-gene analysis. The primers used to amplify the four different genes are given in Table 3[81].
Table 3

Primers used for PCR amplification and sequencing.



Primer name

Primer sequence (5'-3')



16S rDNA









ATP synthase F1 alpha subunit



this study








this study


citrate synthase









subunit I of cytochrome C oxidase



this study




this study




this study




this study



Phylogenetic analysis





Phylogenetic tests


We tested for recombination between Rickettsia strains in two ways. First, we used the maximum χ2 test [87] implemented in RDP v3b22 [88]. This test takes all possible triplets of sequences, removes any gaps, and makes an alignment of just the polymorphic sites. A window is then slid along this alignment in single nucleotide steps. At each position a χ2 statistic is calculated as a measure of the likelihood that recombination has occurred between these sequences. The size of the window was set at approximately 3/4 the numbers of polymorphic sites present for each triplet. To correct for the large number of multiple tests performed, we obtained an analysis-wide significance threshold of χ2 by repeating the analysis on 1000 datasets that were simulated without recombination (simulations performed using Seq-Gen [89]). The maximum χ2 test of recombination is one of the most powerful tests of recombination [90] but it can occasionally falsely infer the presence of recombination under some conditions, such as in regions that contain mutational hot-spots [91]. Therefore we also used the pairwise homoplasy index (PHI) test of recombination [91] implemented in SplitsTree4. The test exploits the fact that when recombination has occurred, sites that are physically close in the sequence should yield compatible phylogenies more often than distant sites. The phi statistic (Φ w ) quantifies the degree of congruence between parsimonious trees at closely-linked sites up to 100 bp (w = 100). A p-value can then be obtained by comparing this statistic with a distribution of values obtained when the position of sites along the sequence is determined at random. To speed computation, this null distribution can be approximated by a normal distribution, whose mean and variance are calculated analytically from the data.

To date key transitions in the order Rickettsiales, we calibrated a 16S rDNA phylogeny of the order using the substitution rate of this gene estimated for the endosymbiont Buchnera [55]. This tree was reconstructed with a molecular clock enforced. We checked that enforcing a clock did not significantly reduce the likelihood of the tree by comparing the likelihoods of a tree with and without a clock enforced using a likelihood ratio test.




Authors’ Affiliations

Institute of Evolutionary Biology, University of Edinburgh
Biology Department, University of Rochester
Agroscope Reckenholz-Tänikon, Research Station ART


  1. Williams KP, Sobral BW, Dickerman AW: A robust species tree for the Alphaproteobacteria. Journal of Bacteriology. 2007, 189 (13): 4578-4586. 10.1128/JB.00269-07.PubMed CentralPubMedGoogle Scholar
  2. Hotopp JC, Lin M, Madupu R, Crabtree J, Angiuoli SV, Eisen JA, Seshadri R, Ren Q, Wu M, Utterback TR, Smith S, Lewis M, Khouri H, Zhang C, Niu H, Lin Q, Ohashi N, Zhi N, Nelson W, Brinkac LM, Dodson RJ, Rosovitz MJ, Sundaram J, Daugherty SC, Davidsen T, Durkin AS, Gwinn M, Haft DH, Selengut JD, Sullivan SA, Zafar N, Zhou L, Benahmed F, Forberger H, Halpin R, Mulligan S, Robinson J, White O, Rikihisa Y, Tettelin H: Comparative Genomics of emerging human ehrlichiosis agents. PLoS Genet. 2006, 2 (2): e21-10.1371/journal.pgen.0020208.Google Scholar
  3. Gross L: How Charles Nicolle of the Pasteur Institute discovered that epidemic typhus is transmitted by lice: Reminiscences from my years at the Pasteur Institute in Paris. Proceedings of the National Academy of Sciences of the United States of America. 1996, 93 (20): 10539-10540. 10.1073/pnas.93.20.10539.PubMed CentralPubMedGoogle Scholar
  4. Gottlieb Y, Ghanim M, Chiel E, Gerling D, Portnoy V, Steinberg S, Tzuri G, Horowitz AR, Belausov E, Mozes-Daube N, Kontsedalov S, Gershon M, Gal S, Katzir N, Zchori-Fein E: Identification and localization of a Rickettsia sp in Bemisia tabaci (Homoptera : Aleyrodidae). Applied and Environmental Microbiology. 2006, 72 (5): 3646-3652. 10.1128/AEM.72.5.3646-3652.2006.PubMed CentralPubMedGoogle Scholar
  5. Fukatsu T, Shimada M: Molecular characterization of Rickettsia sp in a bruchid beetle, Kytorhinus sharpianus (Coleoptera : Bruchidae). Applied Entomology and Zoology. 1999, 34 (3): 391-397.Google Scholar
  6. Weinert LA, Tinsley MC, Temperley M, Jiggins FM: Are we underestimating the diversity and incidence of insect bacterial symbionts? A case study in ladybird beetles. Biology Letters. 2007, 3: 678-681. 10.1098/rsbl.2007.0373.PubMed CentralPubMedGoogle Scholar
  7. Lawson ET, Mousseau TA, Klaper R, Hunter MD, Werren JH: Rickettsia associated with male-killing in a buprestid beetle. Heredity. 2001, 86: 497-505. 10.1046/j.1365-2540.2001.00848.x.PubMedGoogle Scholar
  8. Sakurai M, Koga R, Tsuchida T, Meng XY, Fukatsu T: Rickettsia symbiont in the pea aphid Acyrthosiphon pisum: Novel cellular tropism, effect on host fitness, and interaction with the essential symbiont Buchnera. Applied and Environmental Microbiology. 2005, 71 (7): 4069-4075. 10.1128/AEM.71.7.4069-4075.2005.PubMed CentralPubMedGoogle Scholar
  9. Zchori-Fein E, Borad C, Harari AR: Oogenesis in the date stone beetle, Coccotrypes dactyliperda, depends on symbiotic bacteria. Physiological Entomology. 2006, 31 (2): 164-169. 10.1111/j.1365-3032.2006.00504.x.Google Scholar
  10. Davis MJ, Ying ZT, Brunner BR, Pantoja A, Ferwerda FH: Rickettsial relative associated with papaya bunchy top disease. Current Microbiology. 1998, 36 (2): 80-84. 10.1007/s002849900283.PubMedGoogle Scholar
  11. Schulenburg Van der JHG, Hurst GDD, Huigens TME, van Meer MMM, Jiggins FM, Majerus MEN: Molecular evolution and phylogenetic utility of Wolbachia ftsZ and wsp gene sequences with special reference to the origin of male-killing. Mol Biol Evol. 2000, 17 (4): 584-600.PubMedGoogle Scholar
  12. Perotti MA, Clarke HK, Turner BD, Braig HR: Rickettsia as obligate and mycetomic bacteria. Faseb Journal. 2006, 20: 2372-2374. 10.1096/fj.06-5870fje.PubMedGoogle Scholar
  13. Hagimori T, Abe Y, Date S, Miura K: The first finding of a Rickettsia bacterium associated with parthenogenesis induction among insects. Current Microbiology. 2006, 52 (2): 97-101. 10.1007/s00284-005-0092-0.PubMedGoogle Scholar
  14. Chen DQ, Campbell BC, Purcell AH: A new Rickettsia from a herbivorous insect, the pea aphid Acyrthosiphon pisum (Harris). Current Microbiology. 1996, 33 (2): 123-128. 10.1007/s002849900086.PubMedGoogle Scholar
  15. Schulenburg von der JHG, Habig M, Sloggett JJ, Webberley KM, Bertrand D, Hurst GDD, Majerus MEN: Incidence of male-killing Rickettsia spp. (alpha – proteobacteria) in the ten-spot ladybird beetle Adalia decempunctata L. (Coleoptera : Coccinellidae). Applied and Environmental Microbiology. 2001, 67 (1): 270-277. 10.1128/AEM.67.1.270-277.2001.PubMed CentralPubMedGoogle Scholar
  16. Werren JH, Hurst GDD, Zhang W, Breeuwer JAJ, Stouthamer R, Majerus MEN: Rickettsial Relative Associated with Male Killing in the Ladybird Beetle (Adalia-Bipunctata). Journal of Bacteriology. 1994, 176 (2): 388-394.PubMed CentralPubMedGoogle Scholar
  18. Kikuchi Y, Sameshima S, Kitade O, Kojima J, Fukatsu T: Novel clade of Rickettsia spp. from leeches. Applied and Environmental Microbiology. 2002, 68 (2): 999-1004. 10.1128/AEM.68.2.999-1004.2002.PubMed CentralPubMedGoogle Scholar
  19. Dykova I, Veverkova M, Fiala I, Machackova B, Peckova H: Nuclearia pattersoni sp n. (Filosea), a new species of amphizoic amoeba isolated from gills of roach (Rutilus rutilus), and its rickettsial endosymbiont. Folia Parasitologica. 2003, 50 (3): 161-170.PubMedGoogle Scholar
  20. Vannini C, Petroni G, Verni F, Rosati G: A bacterium belonging to the Rickettsiaceae family inhabits the cytoplasm of the marine ciliate Diophrys appendiculata (Ciliophora, Hypotrichia). Microbial Ecology. 2005, 49 (3): 434-442. 10.1007/s00248-004-0055-1.PubMedGoogle Scholar
  21. Percent SF, Frischer ME, Vescio PA, Duffy EB, Milano V, McLellan M, Stevens BM, Boylen CW, Nierzwicki-Bauer SA: Bacterial community structure of acid-impacted lakes: What controls diversity?. Applied and Environmental Microbiology. 2008, 74 (6): 1856-1868. 10.1128/AEM.01719-07.PubMed CentralPubMedGoogle Scholar
  22. Gihring TM, Moser DP, Lin LH, Davidson M, Onstott TC, Morgan L, Milleson M, Kieft TL, Trimarco E, Balkwill DL, Dollhopf ME: The distribution of microbial taxa in the subsurface water of the Kalahari Shield, South Africa. Geomicrobiology Journal. 2006, 23 (6): 415-430. 10.1080/01490450600875696.Google Scholar
  23. Lu YH, Rosencrantz D, Liesack W, Conrad R: Structure and activity of bacterial community inhabiting rice roots and the rhizosphere. Environmental Microbiology. 2006, 8 (8): 1351-1360. 10.1111/j.1462-2920.2006.01028.x.PubMedGoogle Scholar
  24. Hine PM, Wakefield S, Diggles BK, Webb VL, Maas EW: Ultrastructure of a haplosporidian containing Rickettsiae, associated with mortalities among cultured paua Haliotis iris. Diseases of Aquatic Organisms. 2002, 49 (3): 207-219. 10.3354/dao049207.PubMedGoogle Scholar
  25. Fraune S, Bosch TCG: Long-term maintenance of species-specific bacterial microbiota in the basal metazoan Hydra. Proceedings of the National Academy of Sciences of the United States of America. 2007, 104 (32): 13146-13151. 10.1073/pnas.0703375104.PubMed CentralPubMedGoogle Scholar
  27. Maurelli AT: Black holes, antivirulence genes, and gene inactivation in the evolution of bacterial pathogens. Fems Microbiology Letters. 2007, 267 (1): 1-8. 10.1111/j.1574-6968.2006.00526.x.PubMedGoogle Scholar
  28. Tamura A, Ohashi N, Urakami H, Miyamura S: Classification of Rickettsia-Tsutsugamushi in a New Genus, Orientia Gen-Nov, as Orientia-Tsutsugamushi Comb-Nov. International Journal of Systematic Bacteriology. 1995, 45 (3): 589-591.PubMedGoogle Scholar
  29. Roux V, Raoult D: Phylogenetic analysis of members of the genus Rickettsia using the gene encoding the outer-membrane protein rOmpB (ompB). Int J Syst Evol Microbiol. 2000, 50 Pt 4: 1449-1455.PubMedGoogle Scholar
  30. Roux V, Rydkina E, Eremeeva M, Raoult D: Citrate synthase gene comparison, a new tool for phylogenetic analysis, and its application for the Rickettsiae. International Journal of Systematic Bacteriology. 1997, 47 (2): 252-261.PubMedGoogle Scholar
  31. Sekeyova Z, Roux V, Raoult D: Phylogeny of Rickettsia spp. inferred by comparing sequences of 'gene D', which encodes an intracytoplasmic protein. Int J Syst Evol Microbiol. 2001, 51 (Pt 4): 1353-1360.PubMedGoogle Scholar
  32. Andersson SGE, Stothard DR, Fuerst P, Kurland CG: Molecular phylogeny and rearrangement of rRNA genes in Rickettsia species. Mol Biol Evol. 1999, 16 (7): 987-995.PubMedGoogle Scholar
  33. Vitorino L, Chelo IM, Bacellar F, Ze-Ze L: Rickettsiae phylogeny: a multigenic approach. Microbiology-Sgm. 2007, 153: 160-168. 10.1099/mic.0.2006/001149-0.Google Scholar
  34. Gillespie JJ, Beier MS, Rahman MS, Ammerman NC, Shallom JM, Purkayastha A, Sobral BS, Azad AF: Plasmids and rickettsial evolution: insight from Rickettsia felis. PLoS ONE. 2007, 2 (3): e266-10.1371/journal.pone.0000266.PubMed CentralPubMedGoogle Scholar
  35. Fournier PE, Belghazi L, Robert C, Elkarkouri K, Richards AL, Greub G, Collyn F, Ogawa M, Portillo A, Oteo JA, Psaroulaki A, Bitam I, Raoult D: Variations of plasmid content in Rickettsia felis. PLoS ONE. 2008, 3 (5): e2289-10.1371/journal.pone.0002289.PubMed CentralPubMedGoogle Scholar
  36. Perlman SJ, Hunter MS, Zchori-Fein E: The emerging diversity of Rickettsia. Proceedings of the Royal Society B-Biological Sciences. 2006, 273 (1598): 2097-2106. 10.1098/rspb.2006.3541.PubMed CentralGoogle Scholar
  37. Campbell CL, Mummey DL, Schmidtmann ET, Wilson WC: Culture-independent analysis of midgut microbiota in the arbovirus vector Culicoides sonorensis (Diptera : Ceratopogonidae). Journal of Medical Entomology. 2004, 41 (3): 340-348.PubMedGoogle Scholar
  38. Cho NH, Kim HR, Lee JH, Kim SY, Kim J, Cha S, Kim SY, Darby AC, Fuxelius HH, Yin J, Kim JH, Kim J, Lee SJ, Koh YS, Jang WJ, Park KH, Andersson SG, Choi MS, Kim IS: The Orientia tsutsugamushi genome reveals massive proliferation of conjugative type IV secretion system and host-cell interaction genes. Proceedings of the National Academy of Sciences of the United States of America. 2007, 104: 7981-7986. 10.1073/pnas.0611553104.PubMed CentralPubMedGoogle Scholar
  39. Wiens JJ: Missing data and the design of phylogenetic analyses. Journal of Biomedical Informatics. 2006, 39 (1): 34-42. 10.1016/j.jbi.2005.04.001.PubMedGoogle Scholar
  40. Seshadri R, Kravitz SA, Smarr L, Gilna P, Frazier M: CAMERA: A community resource for metagenomics. Plos Biology. 2007, 5: 394-397. 10.1371/journal.pbio.0050075.Google Scholar
  41. Gillespie JJ, Williams K, Shukla M, Snyder1 EE, Nordberg EK, Ceraul SM, Dharmanolla C, Rainey D, Soneja J, Shallom JM, Czar M, Crasta O, Setubal J, Azad A, Sobral B: Rickettsia Phylogenomics: Unwinding the Intricacies of Obligate Intracellular Life. PLoS ONE. 2008, 3 (4): e2018-10.1371/journal.pone.0002018.PubMed CentralPubMedGoogle Scholar
  42. Baldo L, Werren JH: Revisiting Wolbachia supergroup typing based on WSP: Spurious lineages and discordance with MLST. Current Microbiology. 2007, 55 (1): 81-87. 10.1007/s00284-007-0055-8.PubMedGoogle Scholar
  43. Rappe MS, Connon SA, Vergin KL, Giovannoni SJ: Cultivation of the ubiquitous SAR11 marine bacterioplankton clade. Nature. 2002, 418 (6898): 630-633. 10.1038/nature00917.PubMedGoogle Scholar
  44. Horn M, Fritsche TR, Gautom RK, Schleifer KH, Wagner M: Novel bacterial endosymbionts of Acanthamoeba spp. related to the Paramecium caudatum symbiont Caedibacter caryophilus. Environmental Microbiology. 1999, 1 (4): 357-367. 10.1046/j.1462-2920.1999.00045.x.PubMedGoogle Scholar
  45. Amann R, Springer N, Ludwig W, Gortz HD, Schleifer KH: Identification Insitu and Phylogeny of Uncultured Bacterial Endosymbionts. Nature. 1991, 351 (6322): 161-164. 10.1038/351161a0.PubMedGoogle Scholar
  46. Restif O, Kaltz O: Condition-dependent virulence in a horizontally and vertically transmitted bacterial parasite. Oikos. 2006, 114 (1): 148-158. 10.1111/j.2006.0030-1299.14611.x.Google Scholar
  47. Gibson KE, Rikihisa Y, Zhang CB, Martin C: NeoRickettsia risticii is vertically transmitted in the trematode Acanthatrium oregonense and horizontally transmitted to bats. Environmental Microbiology. 2005, 7 (2): 203-212. 10.1111/j.1462-2920.2004.00683.x.PubMedGoogle Scholar
  48. Werren JH, Baldo L, Clark ME: Wolbachia: master manipulators of invertebrate biology. Nature Reviews Microbiology. 2008, 6 (10): 741-751. 10.1038/nrmicro1969.PubMedGoogle Scholar
  49. MacLeod J, Gordon WS: Studies in tick-borne fever of sheep. I. Transmission by the tick, Ixodes ricinus, with a description of the disease produced. Parasitology. 1933, 25 (2): 273-283.Google Scholar
  50. Norval RAI, Mackenzie PKI: The Transmission of Cowdria-Ruminantium by Amblyomma-Sparsum. Veterinary Parasitology. 1981, 8 (2): 189-191. 10.1016/0304-4017(81)90047-9.Google Scholar
  51. Frances SP, Watcharapichat P, Phulsuksombati D: Vertical transmission of Orientia tsutsugamushi in two lines of naturally infected Leptotrombidium deliense (Acari : Trombiculidae). Journal of Medical Entomology. 2001, 38 (1): 17-21.PubMedGoogle Scholar
  52. Frances SP, Watcharapichat P, Phulsuksombati D, Tanskul P: Transmission of Orientia tsutsugamushi, the aetiological agent for scrub typhus, to co-feeding mites. Parasitology. 2000, 120: 601-607. 10.1017/S0031182099005909.PubMedGoogle Scholar
  53. Ogata H, La Scola B, Audic S, Renesto P, Blanc G, Robert C, Fournier PE, Claverie JM, Raoult D: Genome sequence of Rickettsia bellii illuminates the role of amoebae in gene exchanges between intracellular pathogens. Plos Genetics. 2006, 2: 733-744. 10.1371/journal.pgen.0020076.Google Scholar
  54. Gaunt MW, Miles MA: An insect molecular clock dates the origin of the insects and accords with palaeontological and biogeographic landmarks. Mol Biol Evol. 2002, 19 (5): 748-761.PubMedGoogle Scholar
  55. Moran NA, Munson MA, Baumann P, Ishikawa H: A Molecular Clock in Endosymbiotic Bacteria Is Calibrated Using the Insect Hosts. Proc R Soc Lond Ser B-Biol Sci. 1993, 253 (1337): 167-171. 10.1098/rspb.1993.0098.Google Scholar
  56. Ogata H, Renesto P, Audic S, Robert C, Blanc G, Fournier PE, Parinello H, Claverie JM, Raoult D: The genome sequence of Rickettsia felis identifies the first putative conjugative plasmid in an obligate intracellular parasite. Plos Biology. 2005, 3 (8): 1391-1402. 10.1371/journal.pbio.0030248.Google Scholar
  57. Baldridge GD, Burkhardt NY, Felsheim RF, Kurtti TJ, Munderloh UG: Transposon insertion reveals pRM, a plasmid of Rickettsia monacensis. Applied and Environmental Microbiology. 2007, 73: 4984-4995. 10.1128/AEM.00988-07.PubMed CentralPubMedGoogle Scholar
  58. Blanc G, Ogata H, Robert C, Audic S, Claverie JM, Raoult D: Lateral gene transfer between obligate intracellular bacteria: Evidence from the Rickettsia massiliae genome. Genome Research. 2007, 17: 1657-1664. 10.1101/gr.6742107.PubMed CentralPubMedGoogle Scholar
  59. Baldridge GD, Burkhardt NY, Felsheim RF, Kurtti TJ, Munderloh UG: Plasmids of the pRM/pRF family occur in diverse Rickettsia species. Applied and Environmental Microbiology. 2008, 74 (3): 645-652. 10.1128/AEM.02262-07.PubMed CentralPubMedGoogle Scholar
  60. Jiggins FM: Adaptive evolution and recombination of Rickettsia antigens. Journal of Molecular Evolution. 2006, 62 (1): 99-110. 10.1007/s00239-005-0080-9.PubMed CentralPubMedGoogle Scholar
  61. Amiri H, Davids W, Andersson SGE: Birth and death of orphan genes in Rickettsia. Molecular Biology and Evolution. 2003, 20 (10): 1575-1587. 10.1093/molbev/msg175.PubMedGoogle Scholar
  63. Rasgon JL, Gamston CE, Ren XX: Survival of Wolbachia pipientis in cell-free medium. Applied and Environmental Microbiology. 2006, 72 (11): 6934-6937. 10.1128/AEM.01673-06.PubMed CentralPubMedGoogle Scholar
  64. Heritable microorganisms and reproductive parasitism. Microbial phylogeny and evolution: concepts and controversies. Edited by: Sapp J. New York : Oxford University Press
  65. Hurst GDD, Walker LE, Majerus MEN: Bacterial infections of hemocytes associated with the maternally inherited male-killing trait in British populations of the two spot ladybird, Adalia bipunctata. Journal of Invertebrate Pathology. 1996, 68 (3): 286-292. 10.1006/jipa.1996.0098.PubMedGoogle Scholar
  66. Takahashi M, Urakami H, Yoshida Y, Furuya Y, Misumi H, Hori E, Kawamura A, Tanaka H: Occurrence of high ratio of males after introduction of minocycline in a colony of Leptotrombidium fletcheri infected with Orientia tsutsugamushi. European Journal of Epidemiology. 1997, 13 (1): 79-86. 10.1023/A:1007341721795.PubMedGoogle Scholar
  67. Chiel E, Gottlieb Y, Zchori-Fein E, Mozes-Daube N, Katzir N, Inbar M, Ghanim M: Biotype-dependent secondary symbiont communities in sympatric populations of Bemisia tabaci. Bulletin of Entomological Research. 2007, 97 (4): 407-413. 10.1017/S0007485307005159.PubMedGoogle Scholar
  68. Koga R, Tsuchida T, Fukatsu T: Changing partners in an obligate symbiosis: a facultative endosymbiont can compensate for loss of the essential endosymbiont Buchnera in an aphid. Proc R Soc Lond Ser B-Biol Sci. 2003, 270 (1533): 2543-2550. 10.1098/rspb.2003.2537.Google Scholar
  69. Montllor CB, Maxmen A, Purcell AH: Facultative bacterial endosymbionts benefit pea aphids Acyrthosiphon pisum under heat stress. Ecological Entomology. 2002, 27 (2): 189-195. 10.1046/j.1365-2311.2002.00393.x.Google Scholar
  70. Ferrari J, Darby AC, Daniell TJ, Godfray HCJ, Douglas AE: Linking the bacterial community in pea aphids with host-plant use and natural enemy resistance. Ecological Entomology. 2004, 29 (1): 60-65. 10.1111/j.1365-2311.2004.00574.x.Google Scholar
  71. Oliver KM, Russell JA, Moran NA, Hunter MS: Facultative bacterial symbionts in aphids confer resistance to parasitic wasps. Proceedings of the National Academy of Sciences of the United States of America. 2003, 100 (4): 1803-1807. 10.1073/pnas.0335320100.PubMed CentralPubMedGoogle Scholar
  72. Azad AF, Beard CB: Rickettsial pathogens and their arthropod vectors. Emerging Infectious Diseases. 1998, 4 (2): 179-186.PubMed CentralPubMedGoogle Scholar
  73. Schulenburg J, Habig M, Sloggett JJ, Webberley KM, Bertrand D, Hurst GDD, Majerus MEN: Incidence of male-killing Rickettsia spp. (alpha-proteobacteria) in the ten-spot ladybird beetle Adalia decempunctata L. (Coleoptera : Coccinellidae). Applied and Environmental Microbiology. 2001, 67: 270-277. 10.1128/AEM.67.1.270-277.2001.PubMed CentralPubMedGoogle Scholar
  74. Kontsedalov S, Zchori-Fein E, Chiel E, Gottlieb Y, Inbar M, Ghanim M: The presence of Rickettsia is associated with increased susceptibility of Bemisia tabaci (Homoptera: Aleyrodidae) to insecticides. Pest Manag Sci. 2008, 64 (8): 789-792. 10.1002/ps.1595.PubMedGoogle Scholar
  75. Wedincamp J, Foil LD: Vertical transmission of Rickettsia felis in the cat flea (Ctenocephalides felis Bouche). Journal of Vector Ecology. 2002, 27 (1): 96-101.PubMedGoogle Scholar
  76. Azad AF, Sacci JB, Nelson WM, Dasch GA, Schmidtmann ET, Carl M: Genetic-Characterization and Transovarial Transmission of a Typhus-Like Rickettsia Found in Cat Fleas. Proceedings of the National Academy of Sciences of the United States of America. 1992, 89 (1): 43-46. 10.1073/pnas.89.1.43.PubMed CentralPubMedGoogle Scholar
  77. Kikuchi Y, Fukatsu T: Rickettsia infection in natural leech populations. Microbial Ecology. 2005, 49 (2): 265-271. 10.1007/s00248-004-0140-5.PubMedGoogle Scholar
  78. Stone GN, Schonrogge K, Atkinson RJ, Bellido D, Pujade-Villar J: The population biology of oak gall wasps (Hymenoptera : Cynipidae). Annual Review of Entomology. 2002, 47: 633-668. 10.1146/annurev.ento.47.091201.145247.PubMedGoogle Scholar
  79. Jiggins FM, Tinsley MC: An ancient mitochondrial polymorphism in Adalis bipunctata linked to a sex-ratio-distorting bacterium. Genetics. 2005, 171 (3): 1115-1124. 10.1534/genetics.105.046342.PubMed CentralPubMedGoogle Scholar
  80. Baldo L, Hotopp JCD, Jolley KA, Bordenstein SR, Biber SA, Choudhury RR, Hayashi C, Maiden MCJ, Tettelin H, Werren JH: Multilocus sequence typing system for the endosymbiont Wolbachia pipientis. Applied and Environmental Microbiology. 2006, 72: 7098-7110. 10.1128/AEM.00731-06.PubMed CentralPubMedGoogle Scholar
  81. Lane D: 16S/23S rRNA sequencing. Nucleic Acid Techniques in Bacterial Systematics. Edited by: Stackebrandt E, Goodfellow M. 1991, Chichester; New York: Wiley, 115-175.Google Scholar
  84. Bryant D, Moulton V: Neighbor-Net: An agglomerative method for the construction of phylogenetic networks. Molecular Biology and Evolution. 2004, 21 (2): 255-265. 10.1093/molbev/msh018.PubMedGoogle Scholar
  85. Huson DH, Bryant D: Application of phylogenetic networks in evolutionary studies. Molecular Biology and Evolution. 2006, 23 (2): 254-267. 10.1093/molbev/msj030.PubMedGoogle Scholar
  86. Shimodaira H, Hasegawa M: Multiple comparisons of log-likelihoods with applications to phylogenetic inference. Molecular Biology and Evolution. 1999, 16 (8): 1114-1116.Google Scholar
  87. Maynard Smith J: Analyzing the Mosaic Structure of Genes. Journal of Molecular Evolution. 1992, 34 (2): 126-129.Google Scholar
  89. Rambaut A, Grassly NC: Seq-Gen: An application for the Monte Carlo simulation of DNA sequence evolution along phylogenetic frees. Computer Applications in the Biosciences. 1997, 13 (3): 235-238.PubMedGoogle Scholar


© Weinert et al; licensee BioMed Central Ltd. 2009
