Light supply and mineral nutrition conditions as optimization factors for outdoor mass culture of carotenogenic microalga Dunaliella salina

Abstract

The productivity characteristics of green halophilic algae Dunaliella salina during its pilot cultivation were compared between two nutrient media and under different illumination. Cultivation was carried out in ponds located in the greenhouse during summer season. Two main factors that determine rates of growth and pigments synthesis, as well as the pigments ratio in D. salina grown outdoors in summer, are light and temperature conditions. The mean productivity of D. salina culture grown in two nutrient media, differing in nutrients concentration, was the same, and the mean carotenoid accumulation rate was 30% higher when using Ben-Amotz medium (52 mg·m−2·day−1) than Johnson medium. D. salina cell illumination was decreased by pond shading or by doubling their depth. Both these methods allowed reducing the level of the stress impact on algal culture under extreme light and temperature conditions. Shading of the ponds resulted in an increase in biomass and carotenoid productivity by 30% and 50%. However, a two-fold increase in ponds depth proved to be a more effective technological method, which allowed for an increase in D. salina areal productivity both in biomass and carotenoids by a factor of 3.5–3.8. In conclusion, less concentrated medium and increasing culture depth may be recommended as the optimization factors for D. salina outdoor cultivation.