Bacteria also communicate in a less direct
fashion, sending 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 establish 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 in cultivated soils. When
water or nutrients are in short supply, Myxobacteria begin to excrete 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.
When this threshold is passed, the individual bacteria
begin to 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.
The bacteria coat themselves with another message - Factor
C - to indicate that they are in the correct position and density.
When enough bacteria
are in contact with other bacteria, Factor C triggers the spore forming genes.
Some of the bacteria become spores: thick shelled spheres
that can resist heat, desiccation, and starvation.
The mass of bacteria 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.
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