PhD Dissertation Defense: Natalie Cohen

The Ph.D. Dissertation Defense of Natalie Cohen will be presented at Murray Hall, room G201 of the Marine Sciences Department, UNC at Chapel Hill and live broadcast to UNC IMS (Institute of Marine Science) seminar room 222 in Morehead City – NC. Held on Monday, March 27th, 2017 at 2:30 PM.

Title: Iron-related molecular physiology of marine diatoms: Individual genes to community transcriptomes

Abstract: My dissertation investigates the molecular bases underlying the ability of diatoms to cope under variable vitamin and iron conditions, with an emphasis on the marine pennate diatom genus Pseudo-nitzschia. My laboratory analyses support a direct iron effect on vitamin B₇ (biotin) synthesis where biotin production by diatoms may decrease under iron limitation. Using targeted approaches on the oceanic diatom Pseudo-nitzschia granii as well as several other diatoms in culture, iron storage abilities and gene expression of the iron storage protein, ferritin, under varying iron conditions was assessed. I conclude P. granii is unique in its broad iron quota range and ferritin transcript response, consistent with long-term luxury iron storage. Several of the other diatoms examined contain two distinct ferritin genes that differ in their expression patterns as a function of iron status, with some ferritins actually increasing in expression under iron-limiting conditions. Furthermore, a combination of transcriptomic sequencing and proteomic approaches were performed on iron-replete and iron-limited P. granii. My findings suggest the success of this species in iron-limited waters and during periods of iron enrichment stems from its distinct gene repertoire. In the field, community-wide gene expression analyses of natural diatoms from the Northeast Pacific Ocean indicate changes in iron bioavailability may influence vitamin, nitrate and iron metabolisms, with responses varying depending on taxa and geographical region. Molecular indications of B₁₂ stress in the NE Pacific Ocean following iron enrichment are likely a result of B₁₂ depletion by blooming taxa outpacing B₁₂ production, resulting in B₁₂ limitation. Finally, chronically iron-limited NE Pacific Ocean diatoms demonstrate a distinct transcriptomic response following iron enrichment as compared to coastal diatoms within the California Upwelling Zone that receive a more sporadic iron supply. Collectively my research has provided new insights of how diatoms restructure their iron metabolism and meet their vitamin demands when faced with limiting supplies of these essential nutrients.