Cultivation of four microalgae for biomass and oil production using a two-stage culture strategy with salt stress

A two-stage culture strategy was used for maximum biomass production under nutrient-sufficient conditions, followed by cultivation under low-salt stress, to cause the accumulation of oil in the biomass. Controlled conditions of nitrate, salt concentration, and time to exposure to stress were optimized for oil production with four species of microalgae, Isochrysis galbana, Nannochloropsis oculata, Dunaliella salina, and Dunaliella tertiolecta. Using conditions with addition of nitrate to 24.0 mg/L, I. galbana and N. oculata showed higher biomass productions than D. salina and D. tertiolecta. The oil contents of the microalgae increased from 24.0% to 47.0% in I. galbana with 10 psu for 2 days, from 17.0% to 29.0% in N. oculata with 0 psu for 3 days, from 22.0% to 43.0% of D. salina with 10 psu for 1 day, and from 23.0% to 40.0% (w/w) in D. tertiolecta with 0 psu for 2 days as the second stage culture with low-salt stress. Thus, I. galbana could be a suitable candidate microalga for oil production.