Effects of different light regimes on Dunaliella salina growth and β-carotene accumulation

Abstract

Outdoor cultivations of microalgae for commercial scale production usually rely on natural sunlight following ‘Sine’ regime, but most lab scale studies adopt ‘Block’ or ‘Continuous’ regimes, leading to poor prediction of outdoor cultivation results. To fill this gap on β-carotene production by Dunaliella salina, the effects of light regimes (‘Block’, ‘Sine’, ‘Continuous’) on cell growth and β-carotene accumulation in D. salina were investigated in this study. The results showed significant difference between these regimes. When receiving the same amount of illumination, ‘Sine’ mode inferred 10–55% higher biomass yield and 31–58% higher β-carotene yield than those under the ‘Block’ mode. The biomass concentration, as well as protein and total fatty acid (TFA) content, has no significant difference between different light regimes, but the starch content in the ‘Continuous’ light regime was higher than that of ‘Sine’ and ‘Block’ regime. β-carotene accumulation under ‘Continuous in summer’ and ‘Simulated diurnal irradiance in summer’ regimes were correlated with increase (C18:1, C18:2) and decrease (C16:4, C18:3) of specific fatty acids (FAs) contents, rather than TFA content. Meanwhile, it was found that β-carotene accumulation was correlated with periodical Fv/Fm fluctuations under different light regimes, and indicate that exposure to periodical strong light is more favorable for β-carotene accumulation, rather than continuous light. These results indicated the significance of using ‘Sine’ light regime since it not only provided better predictions on outdoor production, but also helpful for increase biomass and β-carotene productivities.