Scope of Microbiology

Microbiology is the study of microscopic organisms (microbes). Since all life, including visible forms, is composed of cells, however, microbiology is a broad and diverse topic that overlaps with many other disciplines. Microscopic cells, whether prokaryotic (bacteria) or eukaryotic (with nuclei), are the evolutionary and physiological basis of all protoctists, plants, fungi, and animals.

Modern microbiology has become increasingly focused on molecular biology, because the unifying role of DNA and its expression in proteins, most often studied in microbes, cuts across major taxa. Thus microbiology is studied not only explicitly by microbiologists but also in cell biology, genetics (whose use of cell culture mirrors the techniques of microbiology), physiology, pathology, ecology, med icine, forensics, marine sciences, agriculture, forestry, and so on. Many of the academic departments in which microbiology is studied, however, have burgeoned only secondarily from a pure curiosity: this is because of the immense practical uses of many areas of microbiology, from the development of new antibiotics in medicine to more effective techniques for crop improvement, medicine, and human hormone production in genetic engineering.

The financial resources devoted to microbiology have tended to bloat its development in certain directions, notably medicine and soil science, and atrophy it in others. But because medicine focuses on the health of humans and animals, and because microbes are considered causal in many diseases (although not all), microbiology has tended to promote an "us-them" mentality regarding microbes that obscures a more in-depth understanding. Without the financial focus, microbiology might also be considered a science of healthy relations among diverse organisms, including those that oversee the flow of biologically important chemicals on a global scale. In this article, then, we will look at microbiology from a nonmedical perspective that emphasizes the connections of microorganisms and their study to underlying ecological health as well as the disruptions we attend to in sickness.

History of Microbiology

Ironically, the huge interdisciplinary enterprise of microbiology was unknown prior to the seventeenth century. The discovery of the subvisible world had to await the invention of powerful enough microscopes. Although there is no clear date for the origin of the microscope, crude high-magnification lenses (the earliest "microscopes") seem to have been around in Holland by 1590. The Italian scientist Galileo Galilei, known for his astronomical studies, had heard by 1609 of the Dutch tube for mag nifying objects and, within six months, had invented his own version—actually a reverse telescope with 32X magnifying power. Although this was good enough for observing insects, Galileo's friend Johannes Kepler, who studied lenses, described how a more powerful, compound microscope could be built. Such microscopes were used in 1660, notably by the Englishman Robert Hooke, who described the small compartments in cork, the elastic outer tissue of European oak trees, pieces of which he stuck to the head of a pin beneath his magnifier. Because these cubicles reminded him of the living quarters of a monastery, he called them "cells."

Antony van Leeuwenhoek, a Dutch draper, used another microscope design in the 1660s, and found subvisible beings swimming in pond water, feces, human gums, and semen. The latter were, of course, not microbes but wriggling sperm, similar in appearance to microbes and with an evolutionary connection to microbes. It would be two centuries before Charles Darwin's theory of evolution by natural selection would hint that microbes were our evolutionary ancestors—"hint" is the right word, because it was contentious enough to suggest that we had descended from apes, let alone microbes. Microbes, organisms visible only with the microscope, were considered natural curiosities—an interesting sideshow of freakish beings that could be observed in drawing rooms. Like bird-watching, the microbes attracted spectators, but the activity at first had no practical significance outside of pure intellectual curiosity. (That is true of much science that comes to have practical implications, such as Einstein's relativity theories, which led to nuclear power and nuclear bombs.) Calling them "animalcules," Leeuwenhoek described their number as "so extraordinarily great... that [it would] take a thousand million of some of [them] to make up the bulk of a coarse sand-grain."

Since they wriggle and move, and every being not a plant was classified as an animal, these microbes were called "animalcules." Although microbes are really not animals but the evolutionary precursors to all visible life forms, microbiology was ushered in with the discovery by Leeuwenhoek, Hooke, and others of this vast, previously unseen world.

Then, when observation gave way to experiment, further major discoveries were made, some with immense practical consequences. Prior to the evolutionary theory or the evidence of microscopes, it was often thought that life "spontaneously generates": mice arose from rags, flies from veal. In the mid-seventeenth century, however, the British physiologist William Harvey, studying the reproduction and development of the king's deer, showed that every animal comes from an egg. In the seventeenth century the Italian biologist Francesco Redi proved that the maggots in meat came from flies' eggs laid on the meat; and in the eighteenth century, the Italian priest Lazzaro Spal-lanzani established that sperm were necessary for animal reproduction. Although meat did not give rise to maggots when it was covered by a fly-proof net, grape juice, however, still fermented no matter what was put over it. Yet even though it was proved that the larger animals always come from eggs, it seemed obvious that, because of their prevalence, microbes must be generated continually from inorganic matter. Then, by constructing an ingenious piece of glass apparatus with a long curved neck to keep out bacteria and yeasts, French chemist Louis Pasteur proved that microbes arise only from other microbes. His sterile flask remains on exhibit today in Paris at the Institut Pasteur. Today we know that microbes all come from previous microbes, with the major probable exception of the first cell or cells, thought by most scientists to have evolved from cyclical chemical precursors on an energized but not yet living environment.

Modern Microbiology

Pasteur's experiments in the 1850s combined with Charles Darwin's Origin of Species in 1859 set the stage for the development of modern microbiology. The realization of the microbial basis of fermentation, spoiling food, and the associated involvement of microbes in diseased tissues pointed nascent microbiology in the directions of medicine, agriculture, and farming. Microbes were considered germs to be gotten rid of. Today our understanding has become more evolutionary and ecological. Much of the dry weight of our bodies is microbes; our "animal" cells themselves are the result of symbiotic mergers among bacteria. As such, "we" ourselves are microbiological: we require bacteria in our gut, for example, to metabolize vitamin B12. Moreover, one can argue that disease is caused not so much by microscopic germs as by microbial overgrowth, a symptom of a complex ecological body that has come out of balance. Just as we would never ascribe death to the worms in a corpse, we may be too quick to describe disease to the organisms that thrive in its wake. Candida albicans, yeast normally found on human skin, are kept in check by bacteria, also normally found in the human body: yet such microbes can overgrow, appearing to be the sole cause of disease.

More than a thousand antibiotics—substances that prevent the growth of most walled bacteria—have been isolated from bacteria and fungi. Penicillin, a fungal (green mold) exudate from Penicillium crysogenum or P not-statum, a substance that prevents the cell walls of bacteria from forming, is the most famous example. And microbes, of course, are not confined to the human or animal worlds. They also help lay down mineral deposits such as those of iron and manganese. Tiny ocean shelled protists (forams) and algae can be used to find and date oil-bearing sediments. One of the most significant recent developments in microbiology has been the discovery of a "deep hot biosphere." Microbes (so far only bacteria) have been found to thrive inside rocks on chemical transformations in the absence of light. The existence of these subsurface beings increases the chances that life may also exist on, or rather in, other planets. Metabolically diverse bacteria and fungi, breaking down decaying bodies, returning limited elements to the biosphere and its global circulation, and thriving everywhere on the earth's surface from the poles to the equator, the ocean abyss to the guts of astronauts, are the basis of all health as well as sickness.

—Lynn Margulis and Dorion Sagan

See also: Archaebacteria; Arthropods, Terrestrial; Bacteria; Ecology; Evolution; Evolutionary Genetics; Fungi; Medicine, The Benefits of Biodiversity to; Molecular Biology and Biodiversity; Oxygen, History of Presence in the Atmosphere; Paleontology; Pro-toctists; Soil


Dixon, Bernard. 1994. Power Unseen: How Microbes Rule the World. Oxford: W. H. Freeman; Madigan, Michael T., John M. Martinko, and Jack Parker.

1997. "Prokaryotic Diversity: Bacteria." In Brock Biology of Microorganisms. Upper Saddle River, NJ: Prentice Hall; Margulis, Lynn, and Karlene Schwartz.

1998. Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth, 3d ed. New York: W. H. Freeman; Sagan, Dorion, and Lynn Margulis. 1993. Garden of Microbial Delights: A Practical Guide to the Subvisible World. Dubuque, IA: Kendall/Hunt.

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