Date of Award

Fall 12-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Committee Chair

Dr. Shahid Karim

Committee Chair Department

Biological Sciences

Committee Member 2

Dr. Glen Shearer Jr

Committee Member 2 Department

Biological Sciences

Committee Member 3

Dr. Yanlin Guo

Committee Member 3 Department

Biological Sciences

Committee Member 4

Dr. Robert C Bateman Jr

Committee Member 4 Department

Chemistry and Biochemistry

Committee Member 5

Dr. Faqing Huang

Committee Member 5 Department

Chemistry and Biochemistry

Abstract

Ticks are obligate hematophagous arthropods and harbor several pathogens which transmit various diseases to humans and their domesticated animals. Host blood- digestion in a tick midgut (MG) generates several reactive oxygen species (ROS), which are extremely toxic to essential macromolecules (e.g. DNA, proteins, and lipids) within the cell, resulting in high oxidative stress. Thus, this dissertation focuses on the questions of how tick homeostasis responds to high oxidative stress, and how ticks and their harbored pathogens survive the high surge of oxidative stress during blood digestion. We are specifically interested in the tick-pathogen, Rickettsia parkeri (R. parkeri, Rp), harbored by Gulf Coast ticks, which has medical and veterinary significance. Recent literature has suggested the role of redox-switches in tick-pathogen interaction (vector competence). However, the actual mechanism is not well understood. The overall purpose of this study is to investigate the roles of tick antioxidants in tick physiology and their role in facilitating R. parkeri survival during blood feeding. Previous work from our lab has indicated that the manipulation of antioxidants by R. parkeri is required for its survival. Reverse genetics approach was used for the characterization of antioxidants, including selenogenes (SelO and SelS), in uninfected and Rp-infected ticks. The tissue-specific roles of SelO and SelS were demonstrated in Rp colonization. SelO, hypothetically a mitochondrial kinase, likely exploits its antioxidant property for the colonization and survival of Rp in tick MGs. ER stress sensitivity of R. parkeri and tick microbiota were also demonstrated in tick midgut. Prior to this work, exogenous and endogenous oxidative stress were induced into separate group of ticks in order to investigate the response of tick antioxidant machinery as well as the oxidative stress tolerance of ticks. The antioxidant genes, which demonstrated a high shift in their expression, are currently being characterized by our lab. Our results reveal the robustness of the tick antioxidant machinery by exhibiting a high fold upregulation of the antioxidant genes, and as a result, oxidative stress remains very close to control. As a part of this work, antioxidant catalase in ticks is characterized and its role in tick reproductive fitness is demonstrated.

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