Bacteriology
Article by J.C. Ensign, Department of Bacteriology, University of Wisconsin, Madison, Wisconsin.
Key Concepts
• Bacteriology, a specialized branch of microbiology, is the
study of bacteria.
• Bacteria display an incredible physiological diversity.
• One of the most important events in the history of civiliza-
tion was the discovery that bacteria cause disease.
• Bacteria have no discrete, membrane-bound nucleus and
no special intracellular membrane-bound organelles.
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The study of bacteria. The science of bacteriology is a special-
ized branch of microbiology concerned with bacteria (Fig. 1)
Although bacteria are different in some important respects
from all other kinds of cells, their basic processes of physiology
and genetics are the same as in all forms of life. One unusual
property of bacteria as a whole is their physiological diversity.
Some bacteria live in the total absence of oxygen and convert
complex carbohydrates to acids and alcohols (fermenta-
tion), sulfate to hydrogen sulfide, nitrate to nitrogen gas, and
hydrogen plus carbon dioxide to methane gas; other bacteria
carry out photosynthesis by mechanisms nearly identical to
plants; some bacteria can grow and multiply by using energy
obtained from oxidation of sulfur, ammonia, hydrogen, or iron,
while obtaining carbon for cell synthesis from carbon dioxide;
and some can obtain their needed nitrogen from the gas in air.
Humans and the planet Earth are profoundly affected by
bacteria. There is solid evidence that oxygen first appeared in
the air some 2 billion years ago as a result of the activity of bac-
teria. Moreover, bacteria are critically important in the recycling
of materials essential to plants and animals. The degradation
of complex substances such as carbohydrates, proteins, and
lipids, to carbon dioxide allows plants to grow. Conversion of
ammonia to nitrate and of nitrogen gas to amino acids is also
essential to plants. Great numbers of bacteria live on human
skin surfaces as well as in the mouth and intestinal tract; most
of these are benign or even beneficial. Some bacteria, given
the opportunity, can cause severe diseases of humans, other
animals, and plants.
Relationship to other life forms
Bacteria were considered to be primitive plants until approx-
imately 1955, when improved technology of electron micros-
copy made it possible to observe their intracellular structure.
which was found to be much different and simpler than that of
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Content
• Relationship to other life forms
• Bacteria and disease
• Models for biochemistry and genetics
• Biotechnology
Fig. 1: Colorized transmission electron micrograph (TEM) of a Helicobacter pylori bacterium,
which uses its flagella (hairlike strands) for locomotion. This bacterium commonly causes
inflammation of the stomach lining and stomach ulcers.
(Credit: Heather Davies/Science Source)
