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Growth and Metabolism: Running the Microbial Machine |
Chapter: 7
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Glowing in the Dark If you chance to trip over a half-rotten log in the woods at night, you might be surprised to see the exposed parts of the log glowing with a strange, eerie light. This fascinating glow is due to a natural emission of light called bioluminescence. One of nature’s wondrous beauties, it is caused by a number of plants and animals and, in the case of the log, a bevy of fungi and bacteria.
In 1887 the French physiologist Raphael Dubois studied bioluminescence in sea clams and isolated a substance he named luciferin, after Lucifer, the light-bearer. Dubois demonstrated that luciferin would continue to emit light in cold water for several minutes before fading out. However, the light could be restored by adding a fresh extract of clam.
Early in this century, E. Newton Harvey confirmed the report and offered that bioluminescence is a process requiring not only luciferin but also an enzyme called luciferase. He showed that powder from dried clams could be held in the hand and, with a few drops of water, would produce enough light to read a map or letter. In World War II, the Japanese adapted his finding in the field to provide low-intensity light.
It is now known that bioluminescence results from the direct conversion of chemical energy to light energy. Studies of fireflies indicate that the chemical energy is derived from adenosine triphosphate (ATP), as luciferase reacts with luciferin in the presence of oxygen. Studies of bacteria reveal a somewhat different process, in which the role of ATP is still uncertain, but it is clear that oxygen is a prerequisite for the process.
One dramatic example of luminous bacteria is seen in a group of fish popularly called "flashlight fish." These fish, common in the Gulf of Eilat in the Red Sea, maintain populations of luminescent bacteria in organs under their eyes. The bacteria continuously emit light, but the fish can control the light simply by sliding a darkened lid over the bacteria. Light flashes may be useful in sexual mating rituals, locating food sources, warding off predators, or communicating with other fish. The relationship benefits bacteria and fish. The bacteria derive nutrients from their host, while the fish enjoy the advantages of a light-emitting source that requires no batteries.
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