The blacklegged tick, Ixodes scapularis, a species of significant importance to human and animal health, harbors an endosymbiont Rickettsia buchneri sensu stricto. The symbiont is largely restricted to the ovaries, but all life stages can harbor various quantities or lack R. buchneri entirely. The endosymbiont is cultivable in cell lines isolated from embryos of Ixodes ticks. Rickettsia buchneri most readily grows and is maintained in the cell line IRE11 from the European tick, Ixodes ricinus. The line was characterized by light and electron microscopy and used to analyze the growth dynamics of wildtype and GFPuv-expressing R. buchneri. qPCR indicated that the genome copy doubling time in IRE11 was >7 days. Measurements of fluorescence using a plate reader indicated that the amount of green fluorescent protein doubled every 11 days. Two 23S rRNA probes were tested via RNA FISH on rickettsiae grown in vitro and adapted to evaluate the tissue tropism of R. buchneri in field-collected female I. scapularis. We observed strong positive signals of R. buchneri in the ovaries and surrounding the nucleus of the developing oocytes. Tissue tropism in I. scapularis and in vitro growth dynamics strengthen the contemporary understanding of R. buchneri as a transovarially transmitted, non-pathogenic endosymbiont.
Bibliographical noteFunding Information:
Funding: Funding for this project came from US National Institutes of Health grants R01AI81690 and R01AI049424 to Ulrike G. Munderloh.
Acknowledgments: We thank Nicole Y. Burkhardt, Lisa D. Price, Ann T. Palmer, and Gib Ahlstrand for their outstanding technical assistance. We thank Dominika Luciakova from Thermo Fisher Scientific for help with the probe design. We acknowledge support from the University of Minnesota Imaging Center.
© 2021 by the authors. Licensee MDPI, Basel, Switzerland.
- Blacklegged tick
- Growth dynamics
- Ixodes ricinus cell line IRE11
- Ixodes scapularis endosymbiont
- RNA FISH
- Rickettsia buchneri
- Tick cell lines