An investigation into nitrogen uptake by Emilania huxleyi during continuous darkness Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/wp988p081

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  • Experiments were conducted with two strains of the coccolithophorid Emiliania huxleyi. Previous experiments with CCMP1742 and 372 at a light intensity of 60 µEin/m²-s showed that during five-day periods of continuous darkness, strain 1742 was taking up nitrate from the media while strain 372 was not. The nitrate uptake in strain 1742 was concurrent with an increase in particulate nitrogen. This observation, combined with the fact that carbon-rich alkenones decreased during the same dark period, led to the hypothesis that amino acids were being synthesized during the continuous darkness period in E. huxleyi strain 1742. This thesis presents results from three separate continuous darkness experiments with E. huxleyi strains 1742 and 372, run at a light intensity of 165 µEin/m²-s. These experiments were conducted to determine whether 1) amino acids are synthesized in E. huxleyi strain 1742 during continuous darkness, 2) this strain is physiologically unique in this regard, and 3) any amino acid accumulation is compound-specific. Two separate and independent methods for amino acid determination were utilized: gas chromatography paired with a flame ionization detector (GC-FID) and the ninhydrin method. Alkenones, media nutrients, and particulate organic carbon and particulate nitrogen (PN) were also measured. Results showed that no dark-period nutrient uptake or PN accumulation occurred in strain 372, in agreement with previous findings. No accumulation of amino acids was displayed in this strain during the continuous darkness period. CCMP1742 displayed nitrogen uptake, PN accumulation, and amino acid synthesis during the first experiment, but not the second or third experiments. The argument is presented that the increased light intensity of 165 µEin/m²-s inhibited the above dark-period nitrogen dynamics. This inhibition may have been overcome in the first experiment due to a previous nutrient stress experienced by the cells used to inoculate the experiment culture. Future experiments should utilize ¹⁵NO₃ to track the media nitrogen into cells, and also investigate the effects of light intensity and nutrient stress on dark-period protein production.
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