THE IMPORTANCE OF OSMO-MIXOTROPHY IN THE NUTRITION OF THE DIATOM THALASSIOSIRA OCEANICA UNDER IRON LIMITATION
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This thesis addresses the potential for osmo-mixotrophy within the diatom species Thalassiosira oceanica under iron-limited and iron-replete conditions. Urea can provide both carbon and nitrogen to fulfill the cellular requirements of diatoms. Laboratory experiments were conducted with a pure culture of T. oceanica to investigate the relative contribution of urea to carbon and nitrogen uptake in iron-limited and iron-replete diatoms. Isotope labeling experiments with 13C-HCO3onate, 15N-nitrate, and dual labeled 13C/15N urea showed that both N and C from the urea molecule were assimilated into cellular biomass by T. oceanica, though C uptake was at a lower rate than photosynthetic CO2 fixation. In addition, at equal dissolved N concentrations, urea supported a higher biomass than nitrate in iron-limited cultures. There was no significant difference in photosynthetic carbon fixation and nutrient uptake between the iron-limited and the iron-replete cultures.