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The Orientia tsutsugamushi genome reveals massive proliferation of conjugative type IV secretion system and host-cell interaction genes

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Authors
Cho, Nam-Hyuk; Kim, Hang-Rae; Lee, Jung-Hee; Kim, Se-Yoon; Kim, Jaejong; Cha, Sunho; Darby, Alistair C.; Fuxelius, Hans-Henrik; Yin, Jun; Kim, Ju Han; Lee, Sang Joo; Koh, Young-Sang; Jang, Won-Jong; Park, Kyung-Hee; Andersson, Siv G. E.; Choi, Myung-Sik; Kim, Ik-Sang; Kim, Sang-Yoon
Issue Date
2007-05-08
Publisher
National Academy of Sciences
Citation
Proc Natl Acad Sci U S A. 2007 May 8;104(19):7981-6. Epub 2007 May 2.
Keywords
DNA Transposable ElementsGene DuplicationGenetic Variation*Genome, BacterialHumansMultigene FamilyOrientia tsutsugamushi/*genetics/metabolism
Abstract
Scrub typhus is caused by the obligate intracellular rickettsia Orientia tsutsugamushi (previously called Rickettsia tsutsugamushi). The bacterium is maternally inherited in trombicuid mites and transmitted to humans by feeding larvae. We report here the 2,127,051-bp genome of the Boryong strain, which represents the most highly repeated bacterial genome sequenced to date. The repeat density of the scrub typhus pathogen is 200-fold higher than that of its close relative Rickettsia prowazekii, the agent of epidemic typhus. A total of 359 tra genes for components of conjugative type IV secretion systems were identified at 79 sites in the genome. Associated with these are >200 genes for signaling and host-cell interaction proteins, such as histidine kinases, ankyrin-repeat proteins, and tetratrico peptide-repeat proteins. Additionally, the O. tsutsugamushi genome contains >400 transposases, 60 phage integrases, and 70 reverse transcriptases. Deletions and rearrangements have yielded unique gene combinations as well as frequent pseudogenization in the tra clusters. A comparative analysis of the tra clusters within the genome and across strains indicates sequence homogenization by gene conversion, whereas complexity, diversity, and pseudogenization are acquired by duplications, deletions, and transposon integrations into the amplified segments. The results suggest intragenomic duplications or multiple integrations of a massively proliferating conjugative transfer system. Diversifying selection on host-cell interaction genes along with repeated population bottlenecks may drive rare genome variants to fixation, thereby short-circuiting selection for low complexity in bacterial genomes.
ISSN
0027-8424 (Print)
Language
English
URI
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17483455

http://hdl.handle.net/10371/29736
DOI
https://doi.org/10.1073/pnas.0611553104
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College of Medicine/School of Medicine (의과대학/대학원)Microbiology (미생물학전공)Journal Papers (저널논문_미생물학전공)
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