SS2.03 Phytoplankton Ecology Using Molecular Approach
Date: Thursday, June 13, 2002
Time: 2:30:00 PM
Location: Colwood
 
StoeckerDK, UMCES, Horn Point Laboratory, Cambridge, USA, stoecker@hpl.umces.edu
Gustafson, D, E, UMCES, Horn Point Laboratory, Cambridge, USA, gustafsn@hpl.umces.edu
 
Extracellular Protease Activity of Photosynthetic Dinoflagellates
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We used the artificial substrate LEU-AMC to measure leucine aminopeptidase (LAP) activity of dinoflagellates. Axenic Alexandrium tamarense released 1.4 pM AMC/cell/h at 20 C with 70-96% of the activity associated with cells and the remainder in filtrate. Axenic Heterocapsa triquetra released 0.2 pM AMC/cell/h at 15 C and 99% of LAP activity was associated with cells. In non-axenic cultures of Akashiwo sanguinea, Gonyaulax grindleyi, Gyrodinium uncatenum, Karlodinium micrum and Prorocentrum minimum, 60-99% of the total LAP activity was found in the >5 micron fraction. The dinoflagellates were not ruptured by the manipulations and BSA competitively inhibited LAP activity. Thus we believe that proteases are associated with the cell surface. During a mixed species dinoflagellate bloom in an estuary, total LAP activity was positively correlated with dinoflagellate concentration. In red-water samples, up to 76% of LAP activity was in the > 2 micron fraction. Cell surface proteases may play a role in nutrition of mixotrophs by providing amino acids for assimilation. Alternately, amino acids may be degraded by oxidases at the cell surface to provide ammonium.