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Science Frontiers ONLINE No. 58: Jul-Aug 1988 |
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Bacteria
One dictionary's definition:
"Widely distributed group of microscopic, one-celled vegetable organisms..."
As a matter of fact, the nearly universal image of a bacterium is that of a simple, single-cell organism. But:
"That view is now being challenged. Investigators are finding that in many ways an individual bacterium is more analogous to a component cell of a multicellular organism than it is to a free-living, autonomous organism. Bacteria form complex communities, hunt prey in groups and secrete chemical trails for the directed movement of thousands of individuals."
J.A. Shapiro, author of the preceding quote, attributes the simplistic picture of bacteria to medical bacteriology, in which disease-causing bacteria are classically identified by isolating single cells, growing cultures from them, and then showing that they cause the disease in question. In the microscopic real world, bacteria virtually always live in colonies, which possess collective properties quite different and much more impressive than those of the single-cell-in-a-dish! That old human urge for reductionism has led us astray again.
Shapiro seeks to remove the blinders of reductionism in a wonderful article in the June, 1988, issue of Scientific Amer can. We have room here to mention only the Myxobacteria, many of which never exist as single cells in nature. Even those that do are "social" in the sense that, when two cells meet, they align themselves side by side and go through ritual motions that seem foreign to such "simple" organisms! (Where is this "dance" encoded in the single cells? Do they have 'memories'?) Movements within colonies of Myxobacteria are highly coordinated. "Trails of extracellular slime are secreted and serve as highways for the directed movement of thousands of cells, rhythmic waves pulse through the entire population, streams of bacteria move to and from the center and edges of a spreading colony, and bacteria aggregate at specific places within the colony to construct cysts or, in some species, to form elaborate fruiting bodies." The Myxobacteria also collectively form baglike traps to engulf and digest prey. It is apparent now that as simple as a single bacterium may seem, bacterial colonies are pretty complex.
(Shapiro, James A.; "Bacteria as Multicellular Organisms," Scientific American, 258:82, June 1988.)
Comment. How are the collective actions of bacteria effected? Is there a central control center? Oh, oh! We are falling into the reductionist trap again! Life forms do not have to operate like computers do, nor do their functions have to be defined in those block diagrams we like so well. There may be holistic forces involved that escape reductionist thought. It is all very remarkable that bacteria which have been around for billions of years (See article below.) should have acquired such sophistication so quickly, waiting only for the earth to cool a bit.