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Potential for lipid production of diatoms isolated from Adriatic Sea

In recent years marine microalgae have attracted considerable attention due to relatively fast growth coupled with high lipid, carbohydrate, protein and valuable nutrients contents. Among marine microalgae, diatoms (Bacillariophyceae) are the most abundant species in oceans and seas. Owing to favorable fatty acids (FAs) profile abundant in medium chain length, they are considered as suitable feedstock for biodiesel production, as well as alternative source of essential omega-3 FAs due to characteristically high levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Four strains of diatoms isolated from Adriatic Sea were cultivated under phototrophic conditions. Effect of nitrogen on lipid metabolism was studied by varying a sodium nitrate concentration in the culture medium (f/2 medium). The most abundant FAs in diatoms were palmitoleic (13%-43%) followed by palmitic (30%-42%) and myristic (11%-21%) acids, regardless of nitrogen concentration. Nitrogen concentration significantly affected the lipid and FAs content. The content of highly unsaturated FAs, EPA and ARA, in strain 5.4 grown in f/2 medium was 5.42% and 2.58%, respectively. Growth under nitrogen repletion stimulated accumulation of these FAs in diatom ; EPA and ARA content in FAs was 8.24% and 3.75%, respectively. On contrary, growth under the nitrogen limitation decreased the content of both FAs (EPA and ARA content was 2.45% and 0, 4%, respectively). The highest biomass and lipid productivity of 42.5 mg L-1 d-1 and 26.16 mg L-1 d-1, respectively, was obtained under nitrogen repletion conditions. In order to improve lipid and biomass productivity, optimization of culture medium was carried out using 2x, 4x and 10x concentrated f/2 growth medium. Furthermore, batch and fed-batch phototrophic cultivation of strain 5.4 was conducted in a photobioreactor using the optimized growth media.

marine microalgae, Adriatic Sea, lipids, PUFA, nutrients

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