How Bacteria Communicate

Anton van Leeuwenhoek back in 1676 was the first person to see bacteria, Earth's oldest and most abundant beings. Under the microscope bacteria seem to be little more than rigid vessels filled with DNA and an amorphous cytoplasm.

Actually, however, these ancient little creatures are highly sophisticated. They not only communicate between themselves, they also communicate directly with higher plants and animals. In fact, some 2 billion years ago they joined forces with their ancestors called Archaea to form little communities called cells - that's right, the cells forming all the multicellular plants and animals of our world including you.

Communications between individual bacteria are, with slight modifications, familiar to us. For example, bacteria engage in sexual relations.

Their technique is uncomplicated, one bacterium simply pumps DNA right into the another bacteria through an exceedingly thin walled tube. This enables bacteria to share genetic memories and innovations very quickly.

Bacteria also reproduce by fission, simply splitting into two individuals. It seems, however, that unless they also exchange genetic material with others once and awhile the resulting colonies slowly grow old and die.

Bacteria also communicate in a less direct fashion, sending chemical messages to each other that can alter the behavior of thousands of other bacteria at the same time.

To do this, they use small organic molecules called homoserine lactones, or "Autoinducers." Many, if not all bacteria, employ these and related molecules to communicate a variety of environmental parameters, including population density and levels of stress and contentment of the whole community of bacteria.

The communications determine the movements, chemical activities, and reproduction of individual bacteria. This, in turn, leads to changes in the behavior of the whole population. This process has helped to explain complex behavior between bacteria and higher animals, such as the light emitting bacteria of squid.

Myxobacteria offer a perfect example of how communications create the appearance of larger - often very complicated - organisms.

Myxobacteria are rod-shaped bacteria found in cultivated soils.

When water or nutrients are in short supply and Myxobacteria get hungry they squirt out a signal molecule called Factor A. When the density of Factor A passes a certain threshold, it means the bacteria are in danger of starving or desiccation.

Then the individual bacteria move together into clumps of more than 100,000 individuals. Within a short time, their massed bodies form a spherical mound, called a fruiting body, that can be a tenth of a millimeter high.

When the bacteria get into the correct position and there are enough of them they coat themselves with another message - Factor C - to announce they are ready and Factor C triggers spore forming genes in each of the bacteria in their fruiting body.

Some of the bacteria then grow into spores; thick shelled spheres that can resist heat, desiccation, and starvation.

The rest of the bacteria in the fruiting body arrange themselves into very complex shapes, pushing out through rotting wood or vegetation and lifting into the air to facilitate the dispersion of the spores by wind, water or a passing animal.

There are hundreds of different species and each of them constructs the most amazing bodies, complete with little stems, tentacles, and flower-like growths all made of the reorganized bacteria.

When I showed Freddy a picture of the fruiting body of a myxobacterium in the February 1997 issue of Scientific American, I said, "It looks just like a coral polyp. Look at what they built. These bacteria must be a whole lot smarter than we thought."

She replied, "That's nothing, they also create us." And, of course, she was right.

Here is a video of Myxobacteria in action.

Here's how bacteria create lights for animals.

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