If the human eye could resolve images as well as the light microscope, we
would see bacteria and fungi virtually everywhere. They grow in air, water,
foods, and soil, as well as in plant and animal tissue. Any environment that
can support life has its bacterial or fungal population.
Bacteria and fungi affect man in various ways. Some cause human diseases
such as typhoid fever, syphilis, athlete’s foot, tuberculosis, and leprosy, while
others cause plant diseases such as Dutch elm disease, corn smut, late blight
of potatoes, soft rots of vegetables, and crown gall, which is characterized by
tumor formation. Most microorganisms do man little or no harm, however,
and many are vital to our well-being and continued existence on earth.
Bacteria and fungi are involved in the recycling of matter, purification of
sewage, and filtration of water in the soil. They are essential to the
production of cheeses, sauerkraut, pickles, alcoholic beverages, and breads.
Biotechnology firms use microorganisms to produce antibiotics, amino acids,
interferons, enzymes, and human growth hormones.
Bacteria and fungi are convenient organisms for research in genetics,
physiology, cytology, and biochemistry because they grow rapidly, are easy
to manipulate, and require only minimal laboratory space compared to mice
or guinea pigs. As prokaryotes, bacteria have the advantage of being
relatively simple organisms. On the other hand, fungi, which are eukaryotes
and thus much more complex genetically, grow so quickly that a number of
generations can be obtained in only a short period of time.