Effects of urea on cell growth and physiological response in pigment biosynthesis in mixotrophic Chromochloris zofingiensis

The mixotrophic cultivation of Chromochloris zofingiensis (Chlorophyta, Trebouxiophyceae) under various urea concentrations was investigated for biomass and pigment production. The results showed that urea was favorable for biomass production with the highest biomass concentration of 8.86 g L-1 at 3.81 mmol L-1 of urea. When urea concentration was lowered to 0.19 mmol L-1, the highest content (0.99 mg g(-1)) and yield (4.11 mg L-1) of total carotenoids was reached due to an extremely high C/N ratio. Principle component analysis revealed that urea concentrations could indeed affect biomass production and pigment biosynthesis involving intracellular nitrogen assimilation and catabolism associated with chloroplast degradation. Our present study evaluates the feasibility of using urea for C. zofingiensis cultivation and provides new insights for a better understanding of the close relationships between urea metabolism and pigment biosynthesis in mixotrophic C. zofingiensis.