Conjugative transposons and their cargo genes vary across natural populations of Rickettsia buchneri infecting the tick Ixodes scapularis
JournalGenome Biology and Evolution
PublisherOxford University Press
MetadataShow full item record
AbstractRickettsia buchneri (formerly Rickettsia endosymbiont of Ixodes scapularis, or REIS) is an obligate intracellular endoparasite of the black-legged tick, the primary vector of Lyme disease in North America. It is noteworthy among the rickettsiae for its relatively large genome (1.8 Mb) and extraordinary proliferation of mobile genetic elements (MGEs), which comprise nearly 35% of its genome. Previous analysis of the R. buchneri genome identified several integrative conjugative elements named Rickettsiales amplified genomic elements (RAGEs); the composition of these RAGEs suggests that continued genomic invasions by MGEs facilitated the proliferation of rickettsial genes related to an intracellular lifestyle. In this study, we compare the genomic diversity at RAGE loci among sequenced rickettsiae that infect three related Ixodes spp., including two strains of R. buchneri and Rickettsia endosymbiont of Ixodes pacificus strain Humboldt, as well as a closely related species R. tamurae infecting Amblyomma testudinarium ticks. We further develop a novel multiplex droplet digital PCR assay and use it to quantify copy number ratios of chromosomal R. buchneri RAGE-A and RAGE-B to the single-copy gene gltA within natural populations of I. scapularis. Our results reveal substantial diversity among R. buchneri at these loci, both within individual ticks as well as in the I. scapularis population at large, demonstrating that genomic rearrangement of MGEs is an active process in these intracellular bacteria. Copyright The Author(s) 2018.
SponsorsWe would like to thank the West Virginia State Department of Epidemiology (Zoonotic Disease Division) for providing the ticks for this study, and Kevin Macaluso (Louisiana State University School of Veterinary Medicine) for providing R. amblyommatis DNA used as a ddPCR control. We are also grateful to Lucy Weinert (University of Cambridge) for sharing the unpublished genomes of Rickettsia species isolated from the ladybird beetle A. bipunctata and the parasitic ciliate I. multifiliis. This work was supported by West Virginia University start-up funds to T.P.D. J.J.G. acknowledges support from the National Institute of Health/National Institute of Allergy and Infectious Diseases grants R01AI017828, R01AI126853, and R21AI26108. The content is solely the responsibility of the authors and does not necessarily represent the official views of the funding agencies. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the article.
Droplet digital PCR
Integrative conjugative element
Spotted fever group rickettsiae
Identifier to cite or link to this itemhttps://www.scopus.com/inward/record.uri?eid=2-s2.0-85058902876&doi=10.1093%2fgbe%2fevy247&partnerID=40&md5=7a63520bf358dc9ab727808909236f99; http://hdl.handle.net/10713/9030