Date of Award
Spring 5-2017
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Biological Sciences
Committee Chair
Shahid Karim
Committee Chair Department
Biological Sciences
Committee Member 2
Mohamed O. Elasri
Committee Member 2 Department
Biological Sciences
Committee Member 3
Alex S. Flynt
Committee Member 3 Department
Biological Sciences
Committee Member 4
Fengwei Bai
Committee Member 4 Department
Biological Sciences
Committee Member 5
Gregory A. Dasch
Abstract
Amblyomma maculatum (Gulf coast tick) ticks are prevalent across the Atlantic to Gulf Coast region of United States. These ticks are recognized vectors of Rickettsia parkeri, a spotted fever group of Rickettsia (SFGR) known to cause American boutonneuse fever associated with fever and eschar rashes localized to the site of bites. We hypothesized that Rickettsia parkeri colonization and proliferation in the tick vector involve pathogen-symbiont dynamics and tick-pathogen interactions, which influence rickettsial transmission to the victims after tick bites. The rickettsial infection is maintained across the tick life cycle for many generations due to transovarial and transstadial transmission of the pathogen. In the first part, we hypothesized that dynamic interaction among pathogenic R. parkeri and other tick symbionts inside the tick favors the rickettsial pathogen to survive, which multiply and infect vertebrates host upon infestation. We maintained R. parkeri infected and uninfected tick colonies in our lab to study their colonization with I tick. The bacterial loads for R. parkeri, Francisella like endosymbionts and “Candidatus Midichloria mitochondrii” were estimated in both tick colonies during different life stages and within various tick organs that are vital for blood-feeding, reproduction, and disease transmission by using specific qRT-PCR primers. Our results showed that R. parkeri thrives when CMM is present but displaces FLE along the tick life-cycle. In the second part, we hypothesized that tick SECIS binding protein (SBP2) and selenoprotein P (SELENOP) are essential in selenoprotein biosynthesis, and thereby play a role in overall tick redox balance and rickettsial colonization. RNAi assays were employed to specifically silence tick SBP2 and SELENOP. The silencing of SBP2 and SELENOP impaired synthesis of many known selenoproteins except selenophosphate synthetase (SEPHS2) and selenoprotein O (SELENOO). Neither of the genes impaired tick feeding, but SBP2 silencing significantly impacted tick oviposition success and egg hatching. The silencing of SBP2 further impaired rickettsial colonization and reduced transovarial transmission, whereas the SELENOP did not show role in tick feeding success or ovipositioning, but it did impair rickettsial colonization and transovarial transmission. This study provided new avenues of pathogen-symbiont dynamics and tick-pathogen interactions within vectors.
Link to thesis - http://aquila.usm.edu/masters_theses/272/
ORCID ID
orcid.org//0000-0003-1254-792X
Copyright
2017, Khemraj BC
Recommended Citation
Budachetri, Khemraj, "Study of Rickettsia parkeri Colonization and Proliferation in the Tick Host Amblyomma maculatum (Acari: Ixodidae)" (2017). Dissertations. 1381.
https://aquila.usm.edu/dissertations/1381
Included in
Bacterial Infections and Mycoses Commons, Environmental Microbiology and Microbial Ecology Commons, Genomics Commons, Parasitology Commons