WHEN SIMPLE IS NOT SO SIMPLE

The theory of chemical evolution proposes that life on earth developed by spontaneous chemical reaction billions of years ago.

This theory is not that an accident directly transformed lifeless matter into birds, reptiles, or other complex life-forms. Rather, the claim is that a series of spontaneous chemical reactions eventually resulted in very simple life-forms such as algae and other singled-celled organisms.

Based on what is now known about these single-celled organisms, is it reasonable to assume that they are so simple that they could have appeared spontaneously? For example, how simple are single-celled algae? Let’s examine one type in particular, the unicellular green algae of the genus Dunaliella of the order Volvocales.

The single-celled Dunaliella cells are ovoid, or egg-shaped, and very small –about ten microns long. Placed end to end, it would take about 1,000 of them to make one centimeter. Each cell has two whip-like flagella at one end, which allow it to swim. Similar to plants, Dunaliella cells use photosynthesis to provide energy.

They produce food from carbon dioxide. Minerals, and other nutrients absorbed into the cell, and they reproduce by cell division. Dunaliella can live even in a saturated salt solution. It is one of the very few organisms of any kind that can live and propagate in the Dead Sea, which has a salt concentration about eight time that of seawater. This so-called simple organism can also survive sudden changes in the salt concentration of its environment.

Consider, for example, Dunaliella bardawil, found in shallow salt marshes in the Sinai desert. The water in these marshes can be diluted quickly during a thunderstorm or can reach saturated salt concentration when the extreme desert heat evaporates the water. Thanks in part to its ability to produce and accumulate glycerol in just the right amount; this tiny alga can tolerate such extreme changes.

Dunaliella bardawil is able to synthesize glycerol very rapidly, starting within minutes of a change in salt concentrate, either producing or eliminating glycerol as needed in order to adapt. This is important because in some habitats the salt concentration can change considerably within a matter of hours.

The unusual abilities of Dunaliella are remarkable. Yet, these are only a small part of the astounding array of properties used by single-celled organisms to survive and thrive in varying and sometimes hostile environments. These properties enable Dunaliella to respond to growth needs, take in food selectively, exclude harmful substances, excrete wastes, evade or overcome disease, escape predators, reproduce, and so forth. Humans use about 100 trillion cells to accomplish these tasks.

Is it reasonable to say that this single-celled alga is merely a simple, primitive life-form that by happenstance came about from a few amino acids in an organic soup?

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 ample 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 the 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, Dunaliela 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 acidophila, 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 bardawil can survive in high alkaline environments. This demonstrates the extreme range of ecological adaptability of Dunaliella.