POLYSACCHARIDE-DEGRADING ACTIVITIES EXTRACTED DURING GROWTH OF A DINOFLAGELLATE THAT PREYS ON PORPHYRIDIUM-SP

The cells of the red microalga Porphyridium sp. are specifically preyed on by a dinoflagellate, which contains an enzymatic activity that degrades the algal cell wall polysaccharide. The products of this degrading activity extracted from the dinoflagellate on the sixth day of growth were previously characterized by us. In the current study we show that the degrading activity is induced by the dinoflagellate earlier in growth, after 12 h, and that the degradation products differ from those obtained from an enzymatic activity extracted after 6 days of growth. On charge fractionation of the algal polysaccharide degraded by the enzymatic activity, the main differences observed were found in the fraction eluted with water, in which the carbohydrate content of the 12-h preparation was much smaller than that in the 6-day extract (less than half). The opposite situation was found in the hot urea fraction. Gel filtration of the degraded polysaccharide extracted after 12 h of growth revealed three peaks that fit molecular masses of 6000, 300, and 50 kilodaltons plus a fourth peak in the included volume (V(i)) of the column vs. three peaks (4 000-5 000 kDa, 100 kDa and V(i)) for the polysaccharide degraded by enzymes from the sixth day or growth and vs. a 7 000-kDa peak for the native polysaccharide. It seems possible that the 12-h enzymatic activity produces relatively large oligomers that can be split further. Thus, both enzymatic activities (12 h and 6 day) did not fully degrade the polysaccharide, but probably prepared it for further degradation.