Lipid and DNA features of Gonyaulax fragilis (Dinophyceae) as potential biomarkers in mucilage genesis

Abstract

Due to the increasing evidences on dinoflagellate contribution to mucilage phenomena in the Mediterranean Sea, this study was aimed at identifying biochemical and/or genetic markers that could help in relating Gonyaulax fragilis growth with mucilage formation when microscope identification was difficult. The biochemical characterization considered the fatty acid and sterol composition of cultured strains and mucilage samples. The cultured algae displayed the typical fatty acid pattern of dinoflagellates as the 18:0 was the prevalent saturated fatty acid (SFA), 18:1n−7 and 18:1n−9 were the major monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) were dominated by 18:5n−3 and 22:6n−3. Two groups of sterols were identified in algal cells: desmethylsterols, dominated by cholesterol and β-sitosterol, and 4α-methylsterols, having dinosterol as the prevailing sterol. The mucilage lipid pattern was characterized by low amounts of PUFAs and appeared deeply influenced by environment dynamics; however, the 20:5n−3/22:6n−3 ratio <1, the low C16/C18 and 16:1/16:0 ratios evidenced a higher contribution of dinoflagellates to mucilage formation than previously observed. Mucilage sterols showed higher correspondence with those found in G. fragilis than fatty acids. As a genetic marker for G. fragilis a molecular probe that could specifically bind to its 18S rDNA was designed and assayed. The probe displayed a good specificity and sensitivity as it could recognize G. fragilis DNA in the presence of high concentrations of different species, and also in samples having a high complexity and that were partially degraded, as often occurs in field mucilage samples. The results suggest that, among lipid biomarkers, sterols have a higher specificity and persistence than fatty acids and that nucleotide probes could be useful to identify this dinoflagellate in field samples, thus representing a tool to test mucilage samples of uncertain biogenetic origin.