Hemolytic toxicity and nutritional status of Prymnesium parvum during population growth

The haptophyte flagellate Prymnesium parvum forms blooms in brackish waters and produces toxins that harm aquatic organisms. Batch cultures of P. parvum were grown in phosphorus- limited artificial seawater medium with 3 treatments: no aeration or buffering, continuous aeration, and buffering to a high, basic p^H. Over a period of 32 d, frequent samples were taken to determine: cell abundance; cellular composition of carbon (C), nitrogen (N), and phosphorus (P); culture pH; and hemolytic activity. Only pH differed significantly among media treatments: it was basic in all treatments after 10 d of culture, but consistently highest in the buffered medium treatment. In all treatments, exponential population growth was observed during the first 10 d of culture, at rates of about 0.4 to 0.6 d^-1. The cell quota for P declined rapidly over the first 8 d of culture and more slowly thereafter. A transition from exponential growth to stationary phase occurred over 10 to 21 d of culture. Population growth rate was related to cell quota for P according to Droop's equation, with an estimated quota for zero growth of about 5 fmol cell ^-1. In all cultures, high hemolytic activity was seen on Days 8 and 12. All but one culture displayed oscillations of hemolytic activity thereafter. At times of high hemolytic activity, the cell quota for P was <100 fmol cell-1 and the cellular C:P ratio was at or above the Redfield ratio of 106.