pietsch@indiana.edu....... to the Shufflebrain menu

MICROMINDS

the minds of microbes*

BY PAUL PIETSCH

Based on an article in the October, 1983 issue of Science Digest

The human cerebrum is the pride of the thinking world. On its convoluted hemispheres ride the star performers of the nervous system, the 14 billion temperamental neurons that, with their numberless satellites, form the cerebral cortex: six tiers of near liquid, delicate to the point of improbability, sculpted as personally as a face and, under a microscope, like a clear night sky at sea. The cerebral cortex is inseparable from the human condition, from what we are as a species and who we are as individuals.
What lies in more humble reaches of thought?

On the low end of the living spectrum are the bacteria. Headless, heartless, brainless, with a primitive cell for an entire body, one DNA molecule for a chromosome and a life span measured in minutes, some species just make it under the qualifying wire as organisms. The bacteria seem capable of little more than acting and reacting like the spring of a jack-in-the-box. But the denizens of our bowels and toilet bowls, the E. coli and their kissing cousins, have become the subjects of the most rigorously controlled behavioral biological investigations yet conducted. And though they possess not a single neuron, their "thought processes" may have much in common with your thought processes and mine.

A few years ago, I prefaced a lecture on memory with a brief description of bacterial behavior, but soon yielded the floor to a person with a wide grin and a big cigar. "Please forgive my interruption. But I must ask if, in effect, you're saying that the little stinkers think?" I had to admit that I was. For deciding, choosing, judging, data processing and discriminating add up to thinking. Indeed, it is much easier to document certain types of thought in microbes than it is in human beings.

Over a century ago, bacteriologists learned that microorganisms swim toward or away from substances such as chicken soup and mop-pail disinfectant. A German biologist named Wilhelm Pfeffer reported a remarkable observation in 1883. He filled capillary tubes with admixtures of repellents and attractants. With the correct relative proportions, bacteria would swim into a tiny tube after the attractant, even though the repellent by itself would have chased them scurrying in the opposite direction.

What Pfeffer's bacteria did is akin to a person braving a buzzing beehive to get hold of some honey. Call it chemical attraction or behavior or something else, Pfeffer's bacteria had to analyze and compare stimuli and then make a positive choice about what to do. They had to make a decision.

Decisions? Bacteria? After all! Pfeffer's observations moldered in the archives for 90 years. But in 1974, in Science magazine, an article by two microbial biochemists, Julius Adler and Wung- Wai Tso, appeared. Its title: "Decision- Making in Bacteria."

A WHIFF OF PASTRAMI

Using strains of E. coli whose pedigrees were known down to the gene, Adler and his colleagues demonstrated a great many factors in bacterial behavior. They identified specific molecules that attract and repel the microbes, and found that an attractant isn't necessarily a food or a repellent a poison. These are genuine sensory stimuli -- like the whiff of hot pastrami -- the lure being independent of potential nutrition or heartburn.
Another valuable discovery was the nature of the stimulation. Bacteria "perceive" not the absolute amount but the concentration gradient of stimuli -- the increasing strength of a stimulus closer to its source.

Adler and others also studied mutant E coil that cannot be enticed by the very same stimulus that a "normal" microbe finds irresistible. Since mutations mean altered genes, and altered genes mean altered proteins, Adler and others could compare normal and mutant E. coli to discover which proteins were involved in sensory perception. It wasn't long before they had isolated proteins that act as the microbes' sensory receptors.

Biochemist Daniel Koshland, of the University of California, Berkeley, calls these molecules the bacteria's "eyes and ears." In addition to the sensors, a dozen other proteins have been identified as the data processors -- the thinking parts of the bacteria's molecular brain.

Koshland, now a leader in the pursuit of microbial mentality, had initially been intrigued to find that E. coli and their cousins could detect a gradient at all. The analytical data indicated that the cells were discriminating one part per 10,000; that's equivalent to one of us detecting the difference between a jar with 9,999 pennies and one with 10,000. With this minuscule bit of information, the cell would have to think: "Aha! The trail to the goodies is getting hotter in this direction." But how does it do it?

In answering the question, Koshland's group made a monumental discovery: bacteria have a memory. Maybe the cell senses a gradient in space: It could feel a stronger pinch on its "head" than on its "tail." But an E. coli's ends are only 0.000039 of an inch apart. And the microbes are less than half that wide. Not much space, Koshland thought. A swim across or around a drop of sweat for an E. coli would equal a couple of laps across the English Channel for us.

Instead, what if a microbe judged the gradient over time? What if the cell remembers the sensation of a moment ago and matches its present perception against its recollections. Koshland and his colleagues designed a test of the alternatives that seems ingenious to me.

When E. coli are not in a gradient, they tumble randomly. But when they sense graded amounts of attractant, they immediately check the tumbling and swim smoothly on a straight course. Now what would happen if bacteria were in a medium with an attractant mixed in? With no gradient they'd be somersaulting. What if somebody suddenly mixed in more attractant and its molecules diffused throughout the solution? If cells analyze head- to- tail, they'd keep on tumbling because there would be more attractant, but still no gradient. On the other hand, if the cells remember the previous concentration, adding more attractant should fool them into thinking they're in a gradient. And if they do have memory, then they will check the tumbling and begin to swim stably. Koshland tried the experiment, and, sure enough, mixing in more attractant tricked the bacteria; they began to swim smoothly.

This demonstration of bacterial memory is one of the true gems of present- day research. Why? Look up mind in a dictionary, and you'll see memory at the top of the list of synonyms. Memory is to the function of a brain what heat is to a fire: the sine qua non, that without which a brain ceases to be a brain.

There are the inevitable critics of microbial mind power. After all, even by the standards of microcircuits, bacteria are very small. How can all that memory fit into such a tiny space? A human brain fires hundreds of cells when deciding to advance or retreat. A simple neural network in a cat may involve 100,000 interconnections. Indeed, next to even the tiny brain of a salamander an entire bacterium seems like a speck of cosmic dust in a galaxy of stars.

If nothing else, though, science teaches its followers that similarities can hide in unlikely places. And holograms -- those strange 3- D images -- may bear a clue to intelligence in both microbes and human beings.

Holograms share some unique properties with brains. Two generations ago, Karl Lashley showed that memory cannot be culled from the brain and divided into discrete bits and pieces. Lashley taught rats to traverse mazes. The display of memory became dimmer and dimmer as he removed more and more cortex from the animals. Yet even animals with the smallest trace of a cortex could make a good stab at the maze. Certain kinds of holograms can be severely damaged, but the tiny intact parts can produce a whole, if sometimes faded, image.

How can this be? Holograms store images by recording the relative positions or phase relations, of light waves. Phase is built into all cyclic events, from light waves to waves in the ocean. And just as a tsunami and a ripple on a pond can have

the same profile, so, too, phase relationships can be recorded in an area that is very large or very small. If memory functions on the same principle as the hologram, then it could fit into a much tinier space than a human brain, a space much smaller than even an E. coli. It's the pattern of interaction between waves that counts. And the same pattern can have different dimensions. You recognize the president's profile in a new photo just as well as if you had met him in person.

Now let me connect phase to our own brain. Waves carry signals in the form of variations, one wave as compared with another. In an AM radio broadcast, the signal takes the form of modulations of amplitude -- of variations in the size of the waves. But in an FM (frequency modulated) broadcast, the information is literally variations of phase. Frequency and phase are not identical, but both depend on time. And if frequency changes, phase automatically changes too. The impulse of a particular nerve cell cannot vary in amplitude. Instead, when communicating with other cells, the neuron varies the frequency of its impulses. Thus, phase is built into the physiology of the human brain. But phase is right on the surface of the little E. coli.

E. coli bristle with hairlike flagella, so called because they resemble little whips. But they don't snap and crack like a whip, nor do they work back and forth like an oar or flipper. Instead, each flagellum rotates 360 degrees around a central axis and affects the surrounding medium much as a ship's propeller would.

A flagellum is driven by a motor made of proteins. Situated at the base of the flagellum, the motor can speed up, slow down, stop and go into reverse. The driving force comes from streams of protons -- naked hydrogens -- stored near the motor and released in volleys by the chemical action of the sensory processing system. The flagellum's motor is much like that of, say, an electric mixer, but the mixer's is driven by electrons instead of protons. When an E. coli is randomly tumbling through the medium, its flagella are extended to the sides and are spinning out of synchrony with one another. If the motions of the flagella were sounds, the tumbling bacterium would generate veritable cacaphony. But when the cell detects a gradient, something spectacular happens. The flagella begin to spin in sync, and they wind harmoniously together into a rotating tail. The prickly little tumbler metamorphoses into a creature resembling a sperm. The newly acquired tail, its components rhythmically cycling to a common beat, propels the tiny swimmer along a smooth, straight course. As components of a tail, the flagella collectively execute the sonic equivalent of a symphony of survival. How does it do it? On the sensory side, 30 kinds of chemical receptors and a dozen or so proteins that function as data processors lie at or near the inner surface of the cell's membrane. A receptor, activated by a stimulus, fastens itself onto a data processor. The processor, in turn signals two oppositely acting enzymes in the cell membrane. These enzymes chemically change the proteins near the flagella in the cell membrane by either adding or removing a small chemical unit called a methyl group. Each time the group is added, protons are released to run the flagellar motor.

MICROBIAL MEMORY

For those in search of the microbe's memory, there is a very interesting fact about the addition and removal of the methyls. The enzyme systems that perform the two tasks operate at different rates. Those that put on the extra group are faster than those that strip it off. In side the cells, there remains a microscopic chemical record -- a memory -- of events that occurred a few seconds in the past. In the cyclic changes of methyl there is a phase lag -- and phase allows for hologra mic memory. The memory in the methyl lag is of the short-term, or working, variety, the sort of information an organism must forget quickly as circumstances change. For you or me, it might be the recollection that one of us had put some water on to boil. For an E. coli, it is the recollection of a recently sensed concentration. But the working memory contains a version of information encoded in permanent programs. And bacteria seem to have long- term memory and other abilities of "thoughtful" creatures as well.
E. COLI EDUCATION

Koshland points out that when a bacterium shifts from random tumbling to smooth swimming, the cell is simplifying a complex problem. Somersaulting through three dimensions, its flagella cranking every which way, the bacterium would have a dickens of a time sensing, analyzing and figuring out which direction to take. Simplifying complicated problems is one of the hallmarks of intelligent behavior.
Intelligence has other features, one of which is the capacity to learn.

Certain molecules act as sensory stimuli for all cells of a particular strain and can trigger behavior the very first time the cell encounters them. But that's only part of the story. Some molecules become stimuli only if present while the cell is maturing. If a young bacterium does not encounter these molecules at a tender age, it will never develop the mechanisms to perceive them. Thus, bacteria operate by learning as well as by instinct.

I have taught neuroanatomy since 1955 and in all that time have yet to see two identical human brains. Yet under the microscope, E. coli all look alike. Thus, I was stunned by another set of Koshland's observations.

PERSONALITY QUIRKS

Despite identical genes, in spite of the same environment, individual E. coli acquire individual quirks and continue to display them for the rest of their lives. Bacteria exhibit rudimentary personalities. They exhibit traits that are determined by neither heredity nor environment but by chance. A zone of uncertainty -- of individuality, if you will -- surrounds the neighborhood of intelligence in even the lowliest form. And when we start to talk of individuality, that brings a microbial mind very, very close to the realm of human experience.
It's not a question of people and bacteria being the same thing. Nor does it seem likely that genetic engineers can exploit the phase lag in the bacteria's flagellar motor to manufacture human minds in the test tube. But the meek and the mighty perform similar tricks and display common principles. The utter simplicity of the microbial mind brings us nearer to the meaning of our own rub.

*REFERENCES AND ADDITIONAL READINGS

Adler, J. and Tso, W.-W. 'Decision'-making in bacteria: chemotactic response of Escherichia coli to conflicting stimuli. Science 184: 1292-1294, 1974.

Berg, Howard, C. Dynamic properties of flagellar motors. Nature 249: 78-79, 1974.

Fridovich, Irwin Bacterial chemotaxis, Britannica Book of the Year, 1983: 449-495.

Koshland, Daniel E., Jr. A response regulator model in a simple sensory system. Science 196: 1055-1063, 1977.

Koshland, Daniel E., Jr. Bacterial chemotaxis in relation to neurobiology, in Annual Review of Neurosciences 3, ed. by Cowan, W. C. et al, Annual Reviews, Inc., Palo Alto, 1980 pp. 43-75..

Lewin, Roger Is your brain really necessary? Science 210: 1232-1234, 1980.

Silverman, Michael and Simon, Melvin Flagellar rotation and the mechanism of bacterial motility. Nature 249: 73-74, 1974.

You may enjoy "Global Brain: The Evolution of Mass Mind from the Big Bang to the 21st Century" by Howard Bloom

Here are some quotes from the book:

"Reality is a mass hallucination" (p. 193) or "Reality is a Shared Hallucination" (title of Chapter 8; see also page 2 and page 170). This declaration, expressed somewhat differently, is a tenet of Buddhism, but here Bloom makes the case from a scientific point of view, and he makes it very well.

"Humans have been outfoxed...by a collective mind far older and nimbler than any we've developed to this point--the 3.5-billion-year-old global microbial brain." (p. 115) What Bloom is asserting here and throughout the book is that bacteria constitute a superorganism with an intelligence superior to ours that expresses itself through its complex chemistry and tactile behavior.

"...[T]he brain we think belongs solely to our kind achieves its goals by tapping the data banks of eagles, wheat, sheep, rodents, grasses, viruses, and lowly E. coli." (p. 220) This dovetails with "We are modules of a planetary mind..." (p. 219) and "the global brain...is a multispecies thing" (p. 216), and the final line in the text, "We are neurons of this planet's interspecies mind." (p. 223)