Genome size and genetic map of Cowdria ruminantium

Villiers, Etienne P. de; Brayton, Kelly A.; Zweygarth, E.; Allsopp, B. A.

doi:10.1099/00221287-146-10-2627

Cited by 13 publications

(4 citation statements)

References 27 publications

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“…The final assembly contains 25,648 reads with an average length of 569 bp, giving 9.6-fold coverage of the genome. The assembly was finally confirmed by comparison with the physical map (8).…”

Section: Methodsmentioning

confidence: 91%

“…Sequences were assembled by using PHRAP (www.phrap.org) and GAP4 (7) was used for manual checking and editing. Initial contig ordering was performed by comparing the positions of mapped genes and restriction sites to the physical map (8) and by exploiting synteny with the preliminary genomic sequence of Ehrlichia chaffeensis, the closest relative of E. ruminantium for which genomic data are available. The preliminary sequence was made available by The Institute for Genomic Research (www.tigr.org).…”

Section: Methodsmentioning

confidence: 99%

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The genome of the heartwater agent Ehrlichia ruminantium contains multiple tandem repeats of actively variable copy number

Collins

Liebenberg

Villiers

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

153

144

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Heartwater, a tick-borne disease of domestic and wild ruminants, is caused by the intracellular rickettsia Ehrlichia ruminantium (previously known as Cowdria ruminantium). It is a major constraint to livestock production throughout subSaharan Africa, and it threatens to invade the Americas, yet there is no immediate prospect of an effective vaccine. A shotgun genome sequencing project was undertaken in the expectation that access to the complete protein coding repertoire of the organism will facilitate the search for vaccine candidate genes. We report here the complete 1,516,355-bp sequence of the type strain, the stock derived from the South African Welgevonden isolate. Only 62% of the genome is predicted to be coding sequence, encoding 888 proteins and 41 stable RNA species. The most striking feature is the large number of tandemly repeated and duplicated sequences, some of continuously variable copy number, which contributes to the low proportion of coding sequence. These repeats have mediated numerous translocation and inversion events that have resulted in the duplication and truncation of some genes and have also given rise to new genes. There are 32 predicted pseudogenes, most of which are truncated fragments of genes associated with repeats. Rather then being the result of the reductive evolution seen in other intracellular bacteria, these pseudogenes appear to be the product of ongoing sequence duplication events.gene duplication ͉ bacterial genome ͉ molecular sequence data ͉ intracellular adaptation E hrlichia ruminantium (previously known as Cowdria ruminantium) is an obligate intracellular bacterium in the order Rickettsiales. Species in this order cause serious diseases in man and domestic animals throughout the world. E. ruminantium is transmitted by ticks of the genus Amblyomma and causes heartwater, a fatal and economically important disease of wild and domestic ruminants. The disease occurs throughout subSaharan Africa and on several Caribbean islands, from which it threatens to invade the Americas (1), but the existing immunization procedures are rudimentary and relatively ineffective (2). E. ruminantium is a fragile bacterium with exacting culture requirements in eukaryotic cell lines; genetic manipulation has not been attempted, and little is known about its mechanisms of virulence or pathogenesis. Heartwater affects all domestic ruminants, and 80-95% of naïve animals die within 3 weeks, but those that recover have a T cell-mediated immunity to subsequent homologous challenge (3). In the absence of any directed strategy to identify T cell-stimulatory proteins we sequenced the E. ruminantium genome in the expectation that access to the complete protein-coding repertoire of the organism would facilitate the search for vaccine candidate genes.

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Section: Methodsmentioning

confidence: 91%

Section: Methodsmentioning

confidence: 99%

The genome of the heartwater agent Ehrlichia ruminantium contains multiple tandem repeats of actively variable copy number

Collins

Liebenberg

Villiers

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

153

144

View full text Add to dashboard Cite

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“…Heartwater is a tick‐borne ( Amblyomma variegatum , Amblyomma hebraeum, Amblyomma lepidum, Amblyomma maculatum, and other Amblyomma ) infectious disease caused by the rickettsial organism formerly classified as the single member of the Genus Cowdria ( Cowdria ruminantium ), but now classified as Ehrlichia ruminantium 1–3 . E. ruminantium possesses a life cycle that closely resembles that of Chlamydia, with reticular bodies for intracellular reproduction and elementary (dense) bodies for infection of other cells 2 .…”

Section: Introductionmentioning

confidence: 99%

Emerging Tick‐Borne Disease in African Vipers Caused by a Cowdria‐Like Organism

Kiel¹,

Alarcón²,

Parker³

et al. 2006

Annals of the New York Academy of Sciences

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Heartwater is a tick-borne infectious disease caused by the rickettsial organism Cowdria ruminantium, currently Ehrlichia ruminantium. It poses an imminent threat to the Western Hemisphere, where it could cause mortality in cattle and other ruminant livestock in excess of 70%. It has been reported in the Caribbean; and its vector, Amblyomma sparsum, has been found on imported African spurred tortoises (Geochelone sulcata) and leopard tortoises (Geochelone pardalis) in southern Florida in the United States, leading to an importation ban on these reptiles. Symptoms have not been previously reported in reptiles. Here, we report peracute and acute deaths in African vipers imported from Africa through Florida. Signs included vomiting mucoid fluid, diarrhea, emaciation, convulsions, and death. Postmortem showed few gross lesions. The most consistent peracute and acute lesions were the pulmonary lesions and pericarditis with considerable bloody fluid in the pericardial sac (hydropericardium). These lesions strongly resembled the lesions of heartwater and a coccobacillus of less than 1-micron diameter was isolated in viper cell culture. The outbreak was brought to a halt by tick control and treatment of all exposed snakes with tetracycline. This isolation, tetracycline sensitivity, clinical signs, preliminary results with polymerase chain reaction of pCS20 ORF, and the viper preference of the disease may indicate a Cowdria-related attenuated species that has adapted to infect reptiles or an emerging new form of this group of microbes.

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“…nov 1. The organism was cultured in a serum‐free medium,15 and E. ruminantium elementary bodies were purified and genomic DNA prepared as described elsewhere 16…”

Section: Methodsmentioning

confidence: 99%

Development of Improved Vaccines for Heartwater

Collins

Pretorius

Kleef

et al. 2003

Annals of the New York Academy of Sciences

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Heartwater is a tick-borne disease of ruminants which causes major economic losses for domestic livestock owners throughout sub-Saharan Africa and the Caribbean. It is caused by the intracellular rickettsia Ehrlichia (formerly Cowdria) ruminantium and the only commercially available vaccination procedure is over 50 years old. It involves infecting animals with cryopreserved sheep blood containing virulent E. ruminantium organisms, followed by antibiotic treatment when fever develops. Experimental attenuated, inactivated, and nucleic acid vaccine procedures have been investigated over the last half-century, but none of them has yet been particularly successful. We have developed two new experimental vaccines, a live attenuated vaccine and a nucleic acid vaccine. The attenuated vaccine was developed by continuous passage of E. ruminantium organisms of the virulent Welgevonden isolate in a continuous canine macrophage-monocyte cell line. After more than 50 passages the cultures produced no disease when inoculated into mice or sheep, and the inoculated animals were 100% immune to a subsequent lethal homologous needle challenge. The nucleic acid vaccine is based on four E. ruminantium genes from a genetic locus involved in nutrient transport. A cocktail of all four genes, cloned in a DNA vaccine vector and used to immunize sheep, engendered 100% protection against a subsequent lethal needle challenge with the homologous isolate and with each of five different virulent heterologous isolates. Sheep immunized with this cocktail were also exposed to a field challenge in a heartwater-endemic area and few animals survived. This suggests that the local E. ruminantium genotypes were different from any which were administered by needle challenge, or that needle challenge is not a good model for tick challenge in the field.

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Genome size and genetic map of Cowdria ruminantium

Cited by 13 publications

References 27 publications

The genome of the heartwater agent Ehrlichia ruminantium contains multiple tandem repeats of actively variable copy number

The genome of the heartwater agent Ehrlichia ruminantium contains multiple tandem repeats of actively variable copy number

Emerging Tick‐Borne Disease in African Vipers Caused by a Cowdria‐Like Organism

Development of Improved Vaccines for Heartwater

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