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

Cited 181 time in Web of Science Cited 194 time in Scopus
Authors

Cho, Nam-Hyuk; Kim, Hang-Rae; Lee, Jung-Hee; Kim, Se-Yoon; Kim, Jaejong; Cha, Sunho; Kim, Sang-Yoon; Darby, Alistair C.; Fuxelius, Hans-Henrik; Yin, Jun; Kim, Ju Han; Kim, Jihun; Lee, Sang Joo; Koh, Young-Sang; Jang, Won-Jong; Park, Kyung-Hee; Andersson, Siv G. E.; Choi, Myung-Sik; Kim, Ik-Sang

Issue Date
2007-05
Publisher
National Academy of Sciences
Citation
Proceedings of the National Academy of Sciences of the United States of America, Vol.104 No.19, pp.7981-7986
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
URI
https://hdl.handle.net/10371/202700
DOI
https://doi.org/10.1073/pnas.0611553104
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