When Simple Is Not So Simple

Conclusion of Unique Single-Celled Organisms

Living in shallow marshes in the desert, Dunaliella bardawil is exposed to intense sunlight.  This would damage the cell were it not for the protective screening provided by a pigment in the cell. When grown under favorable nutritional conditions, as when nitrogen is available, a Dunaliella culture is bright green, with the green pigment chlorophyll providing the protective screen. Under conditions of nitrogen deficiency and high salt concentration, temperature, and light intensity, the culture changes from green to orange or red.  Why? Under such harsh conditions, a complicated biochemical process takes place.  The chlorophyll content drops to a low level, and an alternative pigment, beta-carotene, is produced instead.  Were it not for its unique ability to produce this pigment, the cell would die.  The appearance of large amounts of beta-carotene-up to 10 percent of this alga's dry weight under these conditions-accounts for the change in color.

In the United States and Australia, to produce natural beta-carotene for the human nutrition market, Dunaliella has been grown commercially in large ponds.  For example, there are large production facilities in southern and western Australia.  Beta-carotene can also be produced  synthetically . However, only two companies have the very costly and complex biochemical plants capable of producing it at production scale. What has taken humans decades and huge investments in research, development, and production facilities, Dunaliella accomplishes very easily.  This simple alga does it with a miniature factory too small to see, in immediate response to the changing requirements of its environment. 

Another unique ability of the genus Dunaliella is found in a species called Dunaliella acidophilam which was first isolated in 1963 in naturally occurring acidic sulfur  springs and soils.  These environments were characterized by a high concentration of sulfuric acid.  In laboratory studies this species of Dunaliella can grow in a solution of sulfuric acid, which is about 100 times more acidic than lemon juice.  On the other hand, Dunaliella bardwil can survive in high alkaline environments. This demonstrates the extreme range of ecological adaptability of Dunaliella. 

Next time: When Simple Is Not So Simple/Some Points to Ponder

From the Awake! magazine