| The coccolithophore Emiliania huxleyi, a cosmopolitan species, is adapted to life across a wide range of conditions from oligotrophic deep ocean waters to more nutrient-rich near-shore habitats. This dissertation examines the relationship between stress and calcification in E. huxleyi . I tested the hypothesis that a strain's ability to calcify confers greater survivability and less perceived stress. I hypothesized, based on the proton ion hypothesis, that the calcifying strain's ability to calcify makes possible a supply of protons (HCO32- + Ca 2+ → CaCO3 + H+) that facilitate nutrient uptake through transporters. The approach entailed an investigation of the response to both nutrient and non-nutrient stressors by monitoring changes in the expression of indicator genes. These genes included the heat shock family (hsp), ubiquitin and polyubiquitin, as well as health indicator genes fucoxanthin chlorophyll binding protein (fcp) and cell division protein (cdp) and two transporters, phosphate and nitrogen transporter . Batch cultures of four calcifying and two non-calcifying strains were maintained under nutrient replete- and non-nutrient-stressed conditions. Expression of the afore-mentioned genes was followed through the use of northern blots and real time RT-PCR. Calcifying strains examined responded to stress exposure by inducing calcification and heat shock proteins, ubiquitin , and polyubiquitin genes. Cells only induced transporters under limitation of their corresponding nutrient. Non-calcifying strains expressed significantly more hsp, ubiquitin, and polyubiquitin indicating that those cells were experiencing higher levels of stress. Both calcifying and non-calcifying strains responded to nutrient-limitation by inducing expression of both phosphate and nitrogen transporter . Survival comparisons of calcifying vs. non-calcifying strains across a variety of stressors and a wide range of concentrations supported the positive correlation between calcification and stress. Taken together, these results support the idea that at the end of a bloom when nutrients are at their lowest levels, protons from calcification provide an added boost to the organism's ability to import nutrients against a steep concentration gradient. |
