High silicate concentration facilitates fucoxanthin and eicosapentaenoic acid (EPA) production under heterotrophic condition in the marine diatom Nitzschia laevis

Nitzschia laevis has the potential for co-production of fucoxanthin and eicosapentaenoic acid (EPA). In this study, the physiological and morphological changes of Nitzschia laevis were investigated under heterotrophic condition with different initial silicate concentrations. High silicate addition stimulated biomass growth and accumulation of fucoxanthin and EPA. The highest yields of biomass (2.41 g/L) and fucoxanthin (32.78 mg/L) were reached with 480 mg/L silicate supplementation. The EPA yield was roughly equal (~70 mg/L) with 240, 480 and 960 mg/L silicate. High silicate concentration (especially 960 mg/L) is a simple strategy to reduce cell aggregation and promote the formation of porous cell structure, which would improve the efficiency of heat and mass transfer during fermentation. In response to high silicate level, extensive metabolic changes are observed, among which the elevated glycolysis and tricarboxylic acid (TCA) cycle might be major contributors to fucoxanthin and fatty acids accumulation by providing additional carbon precursors and energy. This study provided insights for future metabolic engineering to improve fucoxanthin and EPA production in this promising diatom. •The highest yields of biomass and fucoxanthin were reached under 480 mg/L silicate.•Eicosapentaenoic acid yield was higher under 240, 480 and 960 mg/L silicate.•High silicate was a feasible way to obtain independent cells with porous structure.•The elevated glycolysis and tricarboxylic acid cycle provided carbon precursors.