Carotenoid and Fatty Acid Metabolism in Light-Stressed Dunaliella salina

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, -carotene production commenced immediately. The first 4 h after induction were marked by constant intracellular levels of -carotene (2.2 g LCV-1), which resulted from identical increases in the production rates of cell volume and -carotene. Following this initial phase, -carotene productivity continued to increase while the cell volume productivity dropped. As a result, the intracellular -carotene concentration increased reaching a maximum of 17 g LCV-1 after 2 days of light stress. Approximately 1 day before that, the maximum -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 -carotene production facility, indicating a vast potential for improvement. Furthermore, by studying the light-induced changes in both -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 -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