Production of metabolites in microalgae under alkali halophilic growth medium using a dissolved inorganic carbon source

The production of metabolites in microalgae is influenced by extreme cultivation conditions. Bicarbonate is an inorganic carbon source for phototrophic microalgae culturing. In this study, the effect of dissolved inorganic carbon (DIC) (0.4 – 13 g L^-1) on the accumulation of metabolites in Dunaliella tertiolecta biomass is presented. The highest levels of primary metabolites (lipid (239.6 ± 24.3 mg g^-1), protein (336.2 ± 47.5 mg g^-1)), secondary metabolites (total phenolic (12.8 ± 2.0 mg g-1), total flavonoid (14.4 ± 2.3 mg g^-1), total ascorbate (4.7 ± 1.1 mg g^-1)), and pigments (chlorophyll (27.2 ± 3.1 mg g^-1), carotenoid (2.0 ± 0.1 mg g^-1)) were observed when cells were grown with 5.7 g L-1 of DIC (NaHCO₃). The highest biomass concentrations (1.5 ± 0.1 g L^-1) were obtained for cells grown in a mixture of DIC (4.3 + 1.1 g L^-1, NaHCO₃ + Na₂CO₃). This study recommends the optimal levels of bicarbonate carbon of 5.7 g L^-1 for maximising the generation of metabolites in the biomass. It also demonstrates that exogenous excessive DIC in the growth medium would be an effective stressor to produce high-value metabolites in Dunaliella or alkali-halophilic strains.

Statement of Novelty

Overall production of metabolites in D. tertiolecta CCAP 19/30 under high levels of NaHCO₃ (alkalihalophilic medium) has not yet been reported. This study examines the effect of excess dissolved inorganic carbon on the growth of D. tertiolecta in order to maximize biomass yield and yields of the following metabolites: a) primary metabolites (lipid and protein); b) secondary metabolites (total phenolic content, ascorbate, and flavonoid); and c) pigment (chlorophyll and carotenoid). Based on the range of input conditions, the recommended optimal conditions for maximum yield of biomass and metabolites have been provided.