| dc.description.abstract | Diatoms exude large amounts of exopolymers (EPS), which are predominantly composed of carbohydrates. EPS may coagulate into transparent exopolymer particles (TEP). Sticky TEP affects the formation of aggregates and marine snow, and consequently, the efficiency of the biological carbon pump. The objective of this research was to determine how different factors affect carbohydrate production and the formation of TEP by diatoms, and their role in aggregation. Diatoms were grown in laboratory cultures to test the hypothesis that stress increases the cell membrane permeability and subsequently enhances TEP formation. In addition, an experiment was conducted to compare the effect of oxidative stress on both a diatom (Thalassiosira weissflogii) and a cyanobacterium (Synechococcus elongates).
For some diatoms (Thalassiosira weissflogii and Skeletonema marinoi) and the cyanobacterium Synechococcus elongatus, TEP formation was associated with permeable cells. Greater TEP production was observed in cultures under stress conditions (higher temperature, nutrient limitation, and oxidative stress), and more dissolved extracellular carbohydrate was released by dying cells. In the contrast, TEP formation by Cylindrotheca closterium was associated with healthy cells. More dissolved extracellular carbohydrate produced by healthy cells, rather than permeable cells. Therefore, my results indicate that carbohydrate production is important for TEP formation. Stress causes cell leakage, but TEP formation is a complex process. Cell leakage does not always result in the release of dissolved extracellular carbohydrate and enhanced TEP production. In addition, this study investigated the relationship between TEP and aggregate formation. Higher temperature increased TEP production, which was associated with greater aggregation in cultures of S. marinoi, but not in T. weissflogii. Therefore, enhanced TEP production by diatoms does not always affect aggregate formation. This research indicates that environmental factors affect carbohydrate and TEP production by diatoms, and consequently influences aggregate formation. These influences have a profound impact on biogeochemical cycling of carbon. | en |
