Effect of salinity on cell growth and β-carotene production in Dunaliella sp. isolates from Urmia Lake in northwest of Iran
Urmia Lake, the second largest hyper-saline lake by area in the world, has fluctuated in salinity over time, but recently, it has reached a maximum of 360 g/l. Dunaliella is a type of halophile green-orange microalgae especially found in lake and salty fields and is known for its antioxidant activity; because of its ability to create large amount of carotenoids. In the present study, Dunaliella sp. isolates from hypersaline Urmia Lake water were cultured in modified Johnson media and were treated at different salinities (1, 2 and 3 M NaCl), then their cell proliferation rate and β-carotene production were studied. In order to determine the optimal salinity required for the highest β-carotene accumulation, cell count of Dunaliella sp. isolates; total carotenoids and concentration of the β-carotene were determined by direct microscopic counting and spectrophotometry. In the samples with different salinities, the cell count and the β-carotene content of Dunaliella sp. ranged between 0.53 and 2.21x106 cell.ml-1 and 0.2 to 11.4 pg.cell-1, respectively. At the end of the experiments, the maximum cell content mean and the highest β- carotene content mean were obtained at 1 and 3 M NaCl concentrations, as 1.68 x 106 cell.ml-1 and 8.94 pg.cell-1, respectively.
Keywords: Dunaliella, microalgae, Urmia Lake, chlorophyceae, β-carotene.