Growth Pattern and β-Carotene Production of Dunaliella salina Cells in Different Salinities

Dunaliella salina is a green unicellular eukaryote microalga which has no cell wall in its cell structure. In the normal condition of growth it has green color but under stress situation such as high salinity, high light intensity and nutrient deficiency. it turns to yellow. In this state, the cells produce a high amount of the second metabolite such as beta-carotene, glycerol, etc. to maintain their viability. These second metabolites have a high economic value with many applications in the food industry (natural colorant), pharmaceutical industry (pro-vitamin A) and use as additives to food and feed. Nowadays with the significant increase in the world population, it seems necessary to exploit the new alternative sources for energy and food requirement. Microalgae with their unique specifications could be an excellent choice.

In this study, the optimum NaCl concentration for the growth of Dunaliella salina which was purified from Urmia Lake was investigated. Dunaliella salina cells were cultivated under 10000 lx white light intensity within modified Johnson medium. Furthermore, the amount of beta-carotene accumulated within microalgae cells due to 11 steps of 0.5 M salt stresses was measured.

The optimum salt concentration related to the maximum biomass production was recorded in 1 M salinity. The highest amount of beta-carotene was 36.64 µg per ml of cell culture medium in 3.5 M salt concentration. Although beta-carotene content has a descending procedure by salt addition, these amounts were considerable till 6.5 M salinity of the culture medium.

The culture condition can approach to the natural condition by application of salt in jection in small concentration.  In this condition, a significant amount of beta-carotene can be accumulated within the Dunaliella salina cells.