Carotenoid and fatty acid metabolism in light‐stressed Dunaliella salina

Abstract

β-Carotene is overproduced in the alga Dunaliella salina in response to high light intensities. We have studied the effects of a sudden light increase on carotenoid and fatty acid metabolism using a flat panel photobioreactor that was run in turbidostat mode to ensure a constant light regime throughout the experiments. Upon the shift to an increased light intensity, β-carotene production commenced immediately. The first 4 h after induction were marked by constant intracellular levels of β-carotene (2.2 g LCV⁻¹), which resulted from identical increases in the production rates of cell volume and β-carotene. Following this initial phase, β-carotene productivity continued to increase while the cell volume productivity dropped. As a result, the intracellular β-carotene concentration increased reaching a maximum of 17 g LCV⁻¹ after 2 days of light stress. Approximately 1 day before that, the maximum β-carotene productivity of 30 pg cell⁻¹ day⁻¹ (equivalent to 37 mg LRV⁻¹ day⁻¹) was obtained, which was about one order of magnitude larger than the average productivity reported for a commercial β-carotene production facility, indicating a vast potential for improvement. Furthermore, by studying the light-induced changes in both β-carotene and fatty acid metabolism, it appeared that carotenoid overproduction was associated with oil globule formation and a decrease in the degree of fatty acid unsaturation. Our results indicate that cellular β-carotene accumulation in D. salina correlates with accumulation of specific fatty acid species (C16:0 and C18:1) rather than with total fatty acid content. Biotechnol. Bioeng. 2010;106: 638–648.