Increase in the production of allelopathic substances by Prymnesium parvum cells grown under N- or P-deficient conditions

The haptophyte Prymnesium parvum is known to produce a set of highly potent exotoxins, commonly called prymnesins. These toxins have been shown to have several biological activities, including ichthyotoxic, neurotoxic, cytotoxic, hepatotoxic and hemolytic activity towards a range of marine organisms. In addition, recent studies have shown that the toxicity of P. parvum is enhanced when the cells are grown under N- or P-deficient conditions. In this study, the influence of prymnesium toxins on the growth of other phytoplankton species was investigated by addition of cell-free filtrate of P. parvum cultures grown under nutrient-deficient (N or P) or non-deficient conditions. Addition of cell-free filtrate from P. parvum cultures grown under N or P limitation inhibited the growth of Thalassiosira weissflogii, Prorocentrum minimum and Rhodomonas cf. baltica. In contrast, a strain of Prymnesium patelliferum known to produce prymnesium toxins was not negatively affected under any conditions. Furthermore, addition of filtrates from nutrient-sufficient P. parvum cultures did not negatively influence the growth of any of the tested species. These findings suggest that prymnesium toxins may play an allelopathic role, and that the production of allelopathic substances is regulated by the availability of nutrients.