Brainy Bacteria

Bacteria are simple, single-cell organisms that lack the nervous systems and brains of higher life forms. Strange as it may seem, however, the little creatures have a rudimentary form of memory, according to two researchers at the Berkeley campus of the University of California. After performing an intriguing series of experiments, the scientists reported to the annual meeting of the American Chemical Society that the common intestinal bacterium Salmonella typhimurium can recall things in its past.

Biochemists Robert M. Macnab and Daniel Koshland were investigating a characteristic that S. typhimurium shares with many other bacteria: it responds strongly to changes in external stimuli. If, for instance, a hostile substance is introduced into its surroundings, the bacterium uses its flagella --long, hairlike appendages--to swim away from it. But if something attractive is placed near by--say, the sugar, glucose--it will move toward it. How the bacterium chooses its direction is still not fully understood, but it apparently makes its way on a trial-and-error basis. Tumbling to and fro, it senses that taking certain directions increases the strength of a favorable stimulus (or decreases that of an unfavorable one), and it moves accordingly each time.

Studying this phenomenon, the biochemists decided to expose their subjects to two quite different environments in rapid succession. So complete was the changeover (accomplished in less than a second by a high-speed laboratory mixer) that the primitive bacteria should not have been able to detect the switch in surroundings. Yet, surprisingly, the bacteria were not fooled. Shifted from a highly favorable environment to a less desirable one, they began to tumble about in a wildly agitated way, apparently in search of those dimly remembered good surroundings. A short time later, this "memory" faded, and they resumed their normal, only slightly agitated movements. Similarly, when they were transferred from poor environments to better ones, they suddenly started swimming with smooth, undisturbed movements, seemingly relieved to get to more favorable surroundings. After several minutes, they again "forgot" where they had come from and returned to their ordinary movements.

The two researchers cannot yet explain exactly how such primitive "memories" work. But they believe that by studying the bacteria further, scientists may find important clues to the operation of much more complex systems in higher organisms, including man.

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