Influence of different nutrient conditions on cell density, chemical composition and toxicity of Prymnesium parvum (Haptophyta) in semi-continuous cultures

Abstract

The influence of various nitrogen (N) and phosphorus (P) levels on the cell density, chemical composition and toxicity of the marine haptophyte Prymnesium parvum were studied. A non-axenic strain of P. parvum was grown in semi-continuous cultures under either N- or P-limited conditions or nutrient-sufficient conditions (N:P=1:1, 160:1 and 16:1, respectively). Cell toxicity was measured on two occasions at steady state using a haemolytic test. Haemolytic activity was determined as saponin nano-equivalents (SnE) and HE50 (50% haemolysis). Haemolytic activity was demonstrated in all treatments. However, haemolytic activity was significantly higher in P. parvum cells grown under N- or P-limited conditions (287.7±14.0 and 256.8±38.1 SnE cell−1, respectively) compared to cells grown under non-limiting conditions (42.4±3.3 SnE cell−1). Our results document, for the first time, enhanced haemolytic activity in P. Parvum cells irrespective of which nutrient (N or P) was limiting growth. Our results suggest that the toxicity of P. parvum is related to cellular physiological stress, due to nutrient limitation rather than to the direct involvement of either N or P in toxin synthesis.