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Growth and phosphatase activities of Ostreopsis cf. ovata biofilm incubated under diverse dissolved organic phosphorus compounds

Neil Thomas William Ellwood, Marisa Margherita Pasella, Cecilia Totti, Stefano Accoroni*

*Corresponding author:

ABSTRACT: It is becoming increasingly evident that the use of organic nutrients is actually widespread among many aquatic phototrophic organisms. Simultaneously, incidents of eutrophication of coastal waters are becoming more common due to rises in organic nutrient loads deriving from anthropogenic activities and natural terrestrial processes. In the northern Adriatic Sea, blooms of the toxic dinoflagellate Ostreopsis cf. ovata are reported as a frequent phenomenon linked to particular environmental conditions including increased organic nutrient loads. Ostreopsis blooms typically produce a mucilaginous biofilm that can cover all benthic substrata. In order to clarify the role of the Dissolved Organic Phosphorus (DOP) in the onset and maintenance of an Ostreopsis cf. ovata bloom, we investigated the growth rates in the presence of a range of phosphomonoesters (D-Fructose 1,6-disphosphate, β-Glycerophosphate, α-D-Glucose 1-phosphate, Guanosine 5’-monophosphate and Phytic acid) and phosphodiesters (DNA and RNA). Levels of both phosphomonoesterase (PMEase) and phosphodiesterase (PDEase) activities were assessed in the Ostreopsis biofilms. The results showed that Ostreopsis cf. ovata growth is not inhibited in media containing a wide range of DOP and diverse ratios of PME:PDE compared to those containing inorganic phosphorus. Much of the hydrolytic activity was associated with bacteria and with the Extracellular Polymeric Substances (EPS). Based on the present findings, O. cf. ovata success seems to stem from the collective participation of all the components of the biofilm (Ostreopsis, EPS and bacteria) that allows it to thrive in P-limited environments, but where organic P is the main source of P.