The effect of salinity, UV-C, UV-B irradiation stress on the growth, fatty acid and lipid class composition in Dunaliella salina

Dunaliella salina microalgae is a unique eukaryotic microorganism that has a high range of tolerance against environmental fluctuations including salinity, temperature, and light. The aim of this study was to determine the growth factors and content of fatty acids in D. salina under salinity and ultraviolet conditions. The experiments were conducted at three different salinities (150, 200 and 250 ppt) under UVB and UVC irradiations in 3 replicates. Algae growth rate and total algae biomass were measured by counting the number of cells every alternate day for 11 days by hemacytometer. The fatty acids profile was measured by gas chromatography and the amount of total fat using a soxhlet device. The growth rate of algae in most of the treatments under high salinity stress, UVB and UVC irradiation was significantly lower compared to the control group (P≤0.05). The highest cell counts were detected in the control one (2.4 million cells/ml) and UVB-150 treatment (1.98 million cells/ml) on day 7. But despite the higher cell count in the control group, the highest fresh wet weight of algae was obtained in the UVC-200 ppt/salinity group. Substantial differences were detected in the fatty acids profile between the treatments (P≤0.05). Algae cultured under UVB-200 contained the highest PUFA-n3 (20.05%) and the sum of PUFA (32.05%), while the highest PUFA-n6 (13.96%) was found in the UVC-150 group. Algae cultured at 250 ppt salinity without UV irradiation had the highest level (52.75%) of saturated fatty acids (SFA). It was concluded that UV irradiations and high salinity suppresses the growth but improves the synthesis of polyunsaturated fatty acids.