Interactive Effects of Nitrogen and Vitamin B12 limitation on DMSP lyase Activity in the Marine Coccolithophorid,<i> Emiliania huxleyi</i> 373

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McIntosh, Kirk
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Laboratory experiments were performed on the marine coccolithophore <i>Emiliania huxleyi</i> CCMP 373 (<i>E. hux</i>) to determine the effects of vitamin B12 and nitrate limitation on intracellular dimethylsulfoniopropionate (DMSP) concentrations and DMSP-lyase activities (DLA). DLA is an enzyme that is found in certain species of marine algae and bacteria and is responsible for the cleavage of DMSP to dimethylsulfide (DMS). DMS is a volatile organic compound that plays a critical role in the global sulfur cycle due to its ability to form cloud condensation nuclei. </i>E. hux</i> was semi-continuously cultured under four experimental conditions: (1) control treatment with excess nutrients, (2) low nitrate, (3) low vitamin B12, and (4) combined low nitrate/B12. DMSP levels and DLA were measured using a head space analysis technique and a mass spectrometer. Data were normalized using chlorophyll <i>a</i> and cell count measurements. Results revealed no statistical differences in intracellular DMSP or DLA between the experimental groups and the control group, suggesting that DMSP and DLA in <i>E. hux</i> 373 were not directly related to vitamin B12 or nitrate limitation in this experiment. Alternatively, it is possible that intracellular nutrient pools may have accumulated during the nutrient-replete log growth period before the experiment started. Hence, nutrient pooling may have prevented growth limiting conditions in the experimental treatments during the course of the experiment.
<i>Emiliania huxleyi</i>, coccolithophore