On the Factors Which Determine Massive β-Carotene Accumulation in the Halotolerant Alga Dunaliella bardawil

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Abstract
Dunaliella bardawil, a β-carotene-accumulating halotolerant alga, has been analyzed for the effect of various growth conditions on its pigment content, and compared with Dunaliella salina, a β-carotene nonaccumulating species. In D. bardawil, increasing light intensity and light period or inhibiting growth by various stress conditions such as nutrient deficiency or high salt concentration caused a decrease in the content of chlorophyll per cell and an increase in the amount of β-carotene per cell. As a result, the β-carotene-to-chlorophyll ratio increased from about 0.4 to 13 grams per gram and the alga changed its visual appearance from green to deep orange. D. salina grown similarly decreased in content of both chlorophyll and β-carotene per cell and the culture turned from green to yellowish. Low chlorophyll-containing cells of D. bardawil or D. salina exhibit very high photosynthetic rates when expressed on a chlorophyll basis (∼600 micromoles O2 evolved per milligram chlorophyll per hour).