Ethanol as a carotenoid production stimulator in Dunaliella salina CCAP 19/18

Dunaliella salina is a rich source of carotenoids. Carotenoid production is induced under specific conditions, i.e., high light intensity, high salt concentration, nutrient limitation, and suboptimal temperatures in this microalga. The control of environmental factors is vital for high productivity of carotenoids. In this paper, the effect of different ethanol concentrations in combination with nitrogen deficiency was investigated to induce carotenoid production in D. salina CCAP 19/18. Also, some biochemical and molecular parameters were investigated in response to ethanol in the cells. It was shown that ethanol at 0.5% concentration increased cell number but, at 5% concentration, reduced cell viability compared to the control. The highest carotenoid production was achieved at 3% ethanol concentration, which was 1.46 fold higher than the nitrogen deficiency condition. Investigation of the 3 carotenoid biosynthesis genes revealed that their expression levels increased at 3% ethanol concentration, and the phytoene synthase gene was the most upregulated one. Lipid peroxidation increased at both 3% and 5% ethanol concentrations. At 3% concentration, the activity of catalase and superoxide dismutase increased, but no significant changes were seen at 5% ethanol concentration. Peroxidase activity reduced at both 3% and 5% concentrations. Moreover, proline and reducing sugar content increased at 3% concentration while decreased at 5% ethanol concertation. The results showed that at 3% ethanol concentration, higher carotenoid productivity was associated with an increase in other intracellular responses (molecular and biochemical). Ethanol as a controllable element may be beneficial to increase carotenoid production even under inappropriate environmental conditions in D. salina.