Growth dynamics in relation to the production of the main cellular components in the toxic dinoflagellate Ostreopsis cf. ovata

In the last years Ostreopsis cf. ovata blooms are among the most intense of the entire Mediterranean coasts, leading to ecological and human health problems, that are associated to the toxins (palytoxin-like compounds) produced by these algal cells. These compounds are secondary metabolites, whose rate of synthesis depend on the metabolism of their precursors. In general, growth dynamics and toxicity of dinoflagellates reflect the physiological status of the organism. The aim of the present study was to investigate the cellular production of the main biochemical compounds likely involved in the growth and toxicity dynamics of O. cf. ovata during exponential to the late stationary phase in batch cultures of an Adriatic strain. Removal of major nutrients from the medium was monitored along with concentration, biovolume and production of the main cellular components (e.g. polysaccharides, proteins, lipids and toxins). Nutrient uptake, as well as toxin production rates were calculated in the different growth periods. Nutrients (N and P) were completely depleted when cells entered stationary phase and the greatest net toxin production rate (RTOX) occurred during the first days of growth. Profiles of various palytoxins resulted relatively stable during the growth, while their cellular amount within the culture increased during growth. Total and extracellular released polysaccharides, as well as the lipid content greatly increased during the stationary phase, while proteins were mainly produced by cells during the exponential phase. The continuous and constant release of polysaccharides could facilitate cell aggregation and the formation of the benthic community during algal blooms. The trend of growth and production of the main cellular compounds in O. cf. ovata leads us to hypothesize that fast growth of this dinoflagellate, associated with the rapid use of environmental resources (nutrients, and phosphates in particular), may be an ecological/adaptive strategy which could favor this organism in the competition with other species.