The Uncoupled Assimilation of Carbon and Nitrogen from Urea and Glycine by the Bloom-forming Dinoflagellate Prorocentrum minimum.

The spread of harmful dinoflagellate blooms has been linked to the increasing availability of nitrogen, including its dissolved organic forms. The relationships between organic and inorganic nutrient uptake by dinoflagellates are not completely understood; moreover, it is not clear whether organic substances are used exclusively as nitrogen or also as carbon sources. We used laboratory culture experiments to investigate the concurrent uptake of glycine and nitrate by Prorocentrum minimum and estimate a role of two widespread organic substrates, glycine and urea, as carbon sources. Glycine uptake exceeded the uptake of nitrate when both nutrients were present in equal nitrogen amounts. Carbon of urea and glycine constituted only 0.4% and 1.3% of the total carbon uptake by cells, respectively, and this amount of carbon was disproportionately small compared to nitrogen taken up from the same organic substrates indicating uncoupling of organic carbon and nitrogen assimilation. We suggest that the observed uncoupling of organic nitrogen and carbon assimilation is a result of urea and glycine metabolic processing by urease and the glycine decarboxylation complex. We argue that such uncoupling reduces the net dissolved inorganic carbon (DIC) removal by dinoflagellates since the acquisition of nitrogen from urea and glycine leads to DIC release.