The dinoflagellate O.cf. ovata: a small timely and cost-effective biological factory

Ostreopsis species are important components of subtropical and tropical marine environment, as well as of temperate areas. In the last years O. 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. In general, growth dynamics and toxicity of dinoflagellates reflect the physiological status of the organism. So far, there are only few studies concerning the physiological responses of dinoflagellates on different nutrient resources, nutrient uptake, and toxin production dynamics, and they are mainly focused on N-producing toxins algae (e.g. Alexandrium spp.). In the present study the cellular production of the main biochemical compounds which are likely involved in the growth and toxicity dynamics of O. cf. ovata was investigated from the exponential to the late stationary phase using batch cultures of an Adriatic strain. Cultures were established at two different nutrient levels, corresponding to a five-fold diluted f/2 (“standard culture medium”) and to a N,P-limited condition which is comparable to the nutrient concentrations found during the algal blooms in the Adriatic coastal area. Removal of major nutrients from the medium was monitored along with the cell concentration, the biovolume, the cellular elemental composition (in terms of Carbon, Nitrogen, Phosphorus); nutrient uptakes, as well as toxin production rates, were calculated in the different growth periods. Dissolved nutrients resulted totally depleted while cells entered the stationary growth phase and significant differences were observed between the two nutrient conditions. In particular, the content of carbon (C), nitrogen (N), and phosphorus (P) resulted affected by the nutrient availability, as also observed for the toxin production dynamics and their cellular content. The palytoxins amount within the culture was found to increase during the growth, as well as the total and extracellular released polysaccharides and the lipids content, while proteins were mainly produced by cells during the exponential phase. The trend of growth and production of the main cellular compounds in O. cf. ovata leads us to hypothesize that the 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.