Climate Coping: Investigating Metabolic Responses in Crocosphaera watsonii

Climate change causes chemical alterations in the open oceans, such as warming which leads to stratification, affecting nutrient ratios. Changes in nutrient ratios result in species shifts and a change in phytoplankton physiology, affecting all marine life. Unicellular diazotrophic microorganisms play a vital role in our open ocean ecosystems. These organisms do so by implementing metabolic processes that contribute to various availability of nutrients including; nitrogen and carbon. The open ocean diazotrophs are represented by multiple strains of Crocosphaera watsonii. The specific aim of this study was to determine whether the phenotype in small and large strain C. watsonii differs, in response to exposure to altered temperature gradients, measured as changes in cell density, photosynthetic efficiency, and EPS production. Triplicate cultures of C. watsonii WH8501 and C. watsonii WH0003 were inoculated into 60 ml of sterile Vineyard Sound SO media at a 1:10 ratio. Each culture was grown under; warm light levels (∼63 µ E m-2 s-1) on a 14:10 day/night cycle at temperatures of 27^oC or 29^oC. C. watsonii WH8501 cultures were harvested on Day 11, and C. watsonii WH0003 cultures were harvested on Day 9. To evaluate cell growth, fluorescence measurements were taken daily. Aliquots of experimental cultures were evaluated for cell density using flow-cytrometry, photosynthetic efficiency using FIRe fluorescence, and EPS production using a TEP determination assay. Proteins were extracted and analyzed by LC-MS-MS mass spectrometry. There was a correlation between temperature and EPS production for the two strains, C. watsonii WH8501 had a significantly higher growth rate when grown at 29^oC, and a lower growth rate at 27^oC compared to C. watsonii WH0003. Cultures grown at 27^oC produced more EPS than those grown at 29^oC. However, overall C. watsonii WH0003 produced more EPS than C. watsonii WH8501. We an increase in the yield of photosystem II (Fv/Fm) in C. watsonii WH0003 vs. C. watsonii WH8501 vs, suggesting that C. watsonii WH0003 is more efficient at using available photons. A possible explanation for this is that C. watsonii WH0003 may have more efficient CO₂ fixation mechanisms allowing it to fix more CO₂ and excreting the excess carbon in the form of EPS.