Mixotrophic production of polyunsaturated fatty acids and carotenoids by the microalga Nannochloropsis gaditana

Abstract

Microalgae are potential sources of high-value lipids and colorants for use in foods, cosmetics, and other applications. Biomass and metabolite productivities of photoautotrophic algae cultures are low because of limited availability of light. Therefore, mixotrophic cultures were investigated in parallel with photoautotrophic controls. In mixotrophy, some of the energy and carbon are supplied in the form of dissolved organic substrates in addition to inorganic carbon and light being available. The aim was to compare productivities of biomass, fatty acids, and carotenoid pigments in outdoor and indoor mixotrophic and photoautotrophic batch and continuous cultures. The edible and safe marine microalga Nannochloropsis gaditana was used in these studies. The alga could be grown mixotrophically using glucose and glycerol, but not acetate. Optimal concentrations of the organic carbon sources were 5 g L−1 for glucose and 1 g L−1 for glycerol. Mixotrophy substantially increased the biomass concentration and productivity relative to photoautotrophy. The maximum biomass productivity in mixotrophic batch cultures using glucose or glycerol was identical at 170 mg L−1 day−1, being 30% greater than control cultures. In continuous outdoor culture with glucose (5 g L−1) mixotrophy at 12 °C, the total carotenoids in the biomass were 83% higher compared to photoautotrophic control biomass, and the eicosapentaenoic acid (EPA) productivity was 2.2-fold higher relative to controls. The maximum EPA productivity was 11 mg L−1 day−1. Glucose mixotrophy increased the total lipids content in the biomass by 34% relative to photoautotrophic operation.