Graduate Thesis Or Dissertation
 

The Role of Algal Cellular Physiology on the Onset and Maintenance of a Model Cnidarian-Algal Symbiosis

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/ht24ws32f

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  • Coral reefs form vast ecosystems in tropical oceans that are hotspots for biodiversity and are economically valuable. The ecological success of coral reefs is made possible by the symbiotic relationship between corals and dinoflagellate algae from the family Symbiodiniaceae. In this symbiosis, the algae are found within host gastrodermal cells in a membrane-bound organelle called the symbiosome. The success of this symbiosis relies upon an exchange of information between the algal symbiont and coral host. The partners must recognize each other, initiate symbiosis, and homeostatically maintain and regulate the partnership. In this dissertation, I used the sea anemone Exaiptasia diaphana (commonly called Aiptasia), a model system for the study of coral-algal symbiosis, and its symbiont, Breviolum minutum, and explored how algal cell physiology changes with and affects each step of cnidarian-algal symbiosis. In Chapter 2, I characterized how heat stress affects the B. minutum glycome, cell-surface ligands hypothesized to be involved in interpartner recognition. I found that heat-stress of the algal symbiont hindered the establishment of symbiosis and altered the algal glycome to become more like that of non-symbiotic species of Symbiodiniaceae. In Chapters 3 and 4, I described several limitations of using cultured algae to represent algae in the free-living state and studied how expelled algae from Aiptasia in the form of discrete pellets could be a more robust representation of the free-living state in Symbiodiniaceae. I found that algae from egesta are viable and competent symbionts, but are short-lived outside the host. In addition, I determined that algae from egesta had a similar nutritional status to that of algae in the host by studying the expression of several nutrient-related algal genes. These results confirmed my hypothesis that including expelled algae in studies can strengthen the comparison between the symbiotic and free-living states of Symbiodiniaceae and provide new insights into the mechanisms governing cnidarian-algal symbiosis. Finally, in Chapter 5, I developed an aptamer Cell-SELEX (Selective Evolution of Ligands by EXponential enrichment) protocol to characterize symbiotic-state specific cell-surface molecules in B. minutum. Aptamer Cell-SELEX is a promising technology that can enable the discovery of molecules specific to cell phenotypes. In this work, although I could not identify symbiotic-state specific aptamers, I made substantial progress in protocol development and identified critical modifications to improve the chances of success in future attempts. In summary, findings from this work emphasize the role of algal cellular physiology in the success of the cnidarian-algal symbiosis and contribute to a greater understanding of the cellular underpinnings of the cnidarian-dinoflagellate mutualism.
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