Date of Award

Spring 5-2017

Degree Type


Degree Name

Doctor of Philosophy (PhD)


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


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.

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