Plasmids of the pRM/pRF Family Occur in Diverse<i>Rickettsia</i>Species

Baldridge, Gerald D.; Burkhardt, Nicole Y.; Felsheim, Roderick F.; Kurtti, Timothy J.; Munderloh, Ulrike G.

doi:10.1128/aem.02262-07

Cited by 54 publications

(71 citation statements)

References 57 publications

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“…Since the initial discovery of a rickettsial plasmid (pRF of R. felis) (90), a diversity of plasmids has been uncovered in various Rickettsia species (6)(7)(8). Plasmids also have been identified in many poorly characterized Rickettsia species associated primarily with phytophagous arthropods and nonarthropod hosts (121).…”

Section: Resultsmentioning

confidence: 99%

A Rickettsia Genome Overrun by Mobile Genetic Elements Provides Insight into the Acquisition of Genes Characteristic of an Obligate Intracellular Lifestyle

et al. 2012

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We present the draft genome for the Rickettsia endosymbiont of Ixodes scapularis (REIS), a symbiont of the deer tick vector of Lyme disease in North America. Among Rickettsia species (Alphaproteobacteria: Rickettsiales), REIS has the largest genome sequenced to date (>2 Mb) and contains 2,309 genes across the chromosome and four plasmids (pREIS1 to pREIS4). The most remarkable finding within the REIS genome is the extraordinary proliferation of mobile genetic elements (MGEs), which contributes to a limited synteny with other Rickettsia genomes. In particular, an integrative conjugative element named RAGE (for Rickettsiales amplified genetic element), previously identified in scrub typhus rickettsiae (Orientia tsutsugamushi) genomes, is present on both the REIS chromosome and plasmids. Unlike the pseudogene-laden RAGEs of O. tsutsugamushi, REIS encodes nine conserved RAGEs that include F-like type IV secretion systems similar to that of the tra genes encoded in the Rickettsia bellii and R. massiliae genomes. An unparalleled abundance of encoded transposases (>650) relative to genome size, together with the RAGEs and other MGEs, comprise ϳ35% of the total genome, making REIS one of the most plastic and repetitive bacterial genomes sequenced to date. We present evidence that conserved rickettsial genes associated with an intracellular lifestyle were acquired via MGEs, especially the RAGE, through a continuum of genomic invasions. Robust phylogeny estimation suggests REIS is ancestral to the virulent spotted fever group of rickettsiae. As REIS is not known to invade vertebrate cells and has no known pathogenic effects on I. scapularis, its genome sequence provides insight on the origin of mechanisms of rickettsial pathogenicity.

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Section: Resultsmentioning

confidence: 99%

A Rickettsia Genome Overrun by Mobile Genetic Elements Provides Insight into the Acquisition of Genes Characteristic of an Obligate Intracellular Lifestyle

et al. 2012

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“…The presence of two distinct plasmids (pRF and pRF␦) has been reported for R. felis strain URRWXCal2 and in wild-caught R. felis-infected fleas (28). Studies assessing our colonized fleas (24,35) and the R. felis LSU isolate have been able to identify only one plasmid, pRF (3,4). The ultrastructural analysis of R. felis has been examined in the flea host (1, 7) without the report of long-form rickettsiae.…”

Section: Discussionmentioning

confidence: 99%

Characterization and Growth of Polymorphic Rickettsia felis in a Tick Cell Line

Sunyakumthorn

Bourchookarn

Pornwiroon

et al. 2008

Appl Environ Microbiol

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Morphological differentiation in some arthropod-borne bacteria is correlated with increased bacterial virulence, transmission potential, and/or as a response to environmental stress. In the current study, we utilized an in vitro model to examine Rickettsia felis morphology and growth under various culture conditions and bacterial densities to identify potential factors that contribute to polymorphism in rickettsiae. We utilized microscopy (electron microscopy and immunofluorescence), genomic (PCR amplification and DNA sequencing of rickettsial genes), and proteomic (Western blotting and liquid chromatography-tandem mass spectrometry) techniques to identify and characterize morphologically distinct, long-form R. felis. Without exchange of host cell growth medium, polymorphic R. felis was detected at 12 days postinoculation when rickettsiae were seeded at a multiplicity of infection (MOI) of 5 and 50. Compared to short-form R. felis organisms, no change in membrane ultrastructure in long-form polymorphic rickettsiae was observed, and rickettsiae were up to six times the length of typical short-form rickettsiae. In vitro assays demonstrated that short-form R. felis entered into and replicated in host cells faster than long-form R. felis. However, when both short-and long-form R. felis organisms were maintained in cell-free medium for 12 days, the infectivity of short-form R. felis was decreased compared to long-form R. felis organisms, which were capable of entering host cells, suggesting that long-form R. felis is more stable outside the host cell. The relationship between rickettsial polymorphism and rickettsial survivorship should be examined further as the yet undetermined route of horizontal transmission of R. felis may utilize metabolically and morphologically distinct forms for successful transmission.Rickettsia felis is an intracellular gram-negative bacterium transmitted primarily by the cat flea (Ctenocephalides felis). In laboratory colonies of cat fleas, R. felis is maintained via vertical transmission (1, 41). Horizontal transmission of viable R. felis from fleas to vertebrate hosts has not been demonstrated; however, mounting serological and molecular evidence suggests that this agent is infectious to humans (30). The transmission cycle of R. felis in nature involves small mammals, e.g., companion animals, rodents, and opossums, and their fleas (2, 6, 9, 39, 42); however, the mechanism by which R. felis moves from invertebrate to vertebrate host is not known.Several genera of medically important obligate intracellular bacteria, including Chlamydia, Coxiella, Ehrlichia, and Anaplasma, have evolved the ability to produce morphologically distinct infectious forms (5,10,12,18,25,33). Typical rickettsiae are short, rod-shaped organisms with an average size of 0.7 to 2.0 m by 0.3 to 0.5 m; however, atypical rickettsia-like organisms also have been reported in arthropod hosts and cell culture models. Within the tick host, wild-caught Dermacentor andersoni contained hemocyte-associated rickettsia-like organis...

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“…These elements include plasmids in at least 10 species, although it was previously thought that rickettsiae lacked plasmids. One notable aspect of Rickettsia plasmids is that there are multiple plasmids in several species (14). In addition, plasmids in rickettsiae can be polymorphic, as observed for Rickettsia felis, where a plasmid exists in both a 62-kb and a 39-kb form (15).…”

Section: Taxonomic and Genomic Bacteriology: The Revolutionmentioning

confidence: 99%

Update on Tick-Borne Rickettsioses around the World: a Geographic Approach

et al. 2013

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SUMMARY Tick-borne rickettsioses are caused by obligate intracellular bacteria belonging to the spotted fever group of the genus Rickettsia . These zoonoses are among the oldest known vector-borne diseases. However, in the past 25 years, the scope and importance of the recognized tick-associated rickettsial pathogens have increased dramatically, making this complex of diseases an ideal paradigm for the understanding of emerging and reemerging infections. Several species of tick-borne rickettsiae that were considered nonpathogenic for decades are now associated with human infections, and novel Rickettsia species of undetermined pathogenicity continue to be detected in or isolated from ticks around the world. This remarkable expansion of information has been driven largely by the use of molecular techniques that have facilitated the identification of novel and previously recognized rickettsiae in ticks. New approaches, such as swabbing of eschars to obtain material to be tested by PCR, have emerged in recent years and have played a role in describing emerging tick-borne rickettsioses. Here, we present the current knowledge on tick-borne rickettsiae and rickettsioses using a geographic approach toward the epidemiology of these diseases.

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Plasmids of the pRM/pRF Family Occur in DiverseRickettsiaSpecies

Cited by 54 publications

References 57 publications

A Rickettsia Genome Overrun by Mobile Genetic Elements Provides Insight into the Acquisition of Genes Characteristic of an Obligate Intracellular Lifestyle

A Rickettsia Genome Overrun by Mobile Genetic Elements Provides Insight into the Acquisition of Genes Characteristic of an Obligate Intracellular Lifestyle

Characterization and Growth of Polymorphic Rickettsia felis in a Tick Cell Line

Update on Tick-Borne Rickettsioses around the World: a Geographic Approach

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