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theses

Nitric oxide (NO) is a gaseous, membrane-permeable free radical that has emerged in recent decades as a ubiquitous inter- and intra-cellular signaling molecule in all kingdoms of life. Despite the abundance of work elucidating the physiological functions of NO, a number of important open questions remain about its biology, especially in photosynthetic organisms. This dissertation expands the current state of knowledge of NO ecophysiology to the marine phytoplankton Emiliania huxleyi. E. huxleyi is a globally important bloom-forming species of coccolithophore, a group of calcifying eukaryotic marine algae. E. huxleyi exerts a profound influence on the marine ecosystem in a number of ways including producing a significant portion of marine calcium carbonate, fixing inorganic carbon, modulating biogeochemical cycling of important elements, and impacting climate. E. huxleyi is perhaps best known for its vast blooms being routinely infected and terminated by viral infection. This work shows that NO production is a hallmark of early- to mid-lytic viral infection both in laboratory cultures and in natural E. huxleyi populations encountered in the North Atlantic. It provides evidence that NO produced during infection may have an antioxidant function by upregulating and activating the diverse enzymatic antioxidant machinery, minimizing intracellular oxidative stress during infection so that viruses may replicate and assemble in a redox favorable environment. This dissertation further explores the relationship between NO production, oxidative stress, and antioxidant activity by surveying these traits in various laboratory E. huxleyi strains that differ in their inherent susceptibility to viral infection. Significant intra-species variability was observed in the production of NO across a gradient of viral susceptibility, along with gradients in basal antioxidant capacity and production of reactive oxygen species (ROS). The possible relationship between NO, ROS, and antioxidant activity is discussed, as well as implications for costs-of-resistance. An important outcome of this work is the observation that intracellular NO patterns are manifested in the extracellular milieu, indicating that algal diversity and physiology may be important in dictating whether marine microbial populations represent a net source of NOx to the environment. Lastly, this work sheds light on the possible biosynthetic pathways of NO and the NO-mediated protein post-translational modifications relevant to E. huxleyi. This dissertation concludes with a summary of the main findings along with a discussion of the broader impacts, open questions, and future directions.

ETD_9847

Ph.D.

Includes bibliographical references

doi:10.7282/t3-xyvc-2412

ETD doctoral

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