Semicontinuous nitrogen limitation as convenient operation strategy to maximize fatty acid production in Neochloris oleoabundans

Neochloris oleoabundans is a green microalga known for the ability to increase its fatty acid (FA) content when grown under nitrogen (N) depletion. Accumulation of FAs and their composition were compared by cultivating N. oleoabundans in N limitation and N depletion conditions. We adopted an innovative approach that consists in semicontinuous cultivation mode as a strategy to optimize lipid accumulation. To identify the optimal conditions for the production of different FAs, a temporal profile of how different conditions may influence the microalgae culture in terms of biomass, FA concentration and composition was evaluated. N limited culture attained higher values of algal productivity and total FA concentration (0.42 mg L− 1 d− 1 and 91.2 mg L− 1) than N deplete culture (0.15 mg L− 1 d− 1 and 53.2 mg L− 1). Considering lipid accumulation, concentration and percentage of triacylglycerols (TAG) increased in all culture methods, with respect to the N replete control. In particular, N limitation led to a significant increase of polyunsaturated TAG (PUFA), while N depletion led to the highest level of monounsaturated TAG. These results suggest that N. oleoabundans biomass and FAs were strongly affected by the N supply and that the quality of the TAG fraction could be modulated in accordance to the utilization purpose in a wide range of applications. Semicontinuous culture resulted as a promising operational strategy for FAs production. More specifically, semicontinuous cultivation coupled to N limitation was found to be a convenient method to increment PUFA fraction and therefore to yield a high value product.