Phosphatase activity in the heterotrophic dinoflagellate Pfiesteria shumwayae

The ELF-97 phosphatase substrate was used to examine phosphatase activity in four strains of the estuarine heterotrophic dinoflagellate, Pfiesteria shumwayae. Acid and alkaline phosphatase activities also were evaluated at different pH values using bulk colorimetric methods. Intracellular phosphatase activity was demonstrated in P. shumwayae cells that were actively feeding on a fish cell line and in food limited cells that had not fed on fish cells for 3 days. All strains, whether actively feeding or food limited showed similar phosphatase activities. P. shumwayae cells feeding on fish cells showed ELF-97 activity near, or surrounding, the food vacuole. Relatively small, spherical ELF-97 deposits were also observed in the cytoplasm and sometimes near the plasma membrane. ELF-97 fluorescence was highly variable among cells, likely reflecting different stages in digestion and related metabolic processes. The location of enzyme activity and supporting colorimetric measurements suggest that, as in other heterotrophic protists, acid phosphatases predominate in P. shumwayae and have a general catabolic function.