Small and deceptively simple, procaryotes are among nature's most abundant and ubiquitous microorganisms. If it were somehow possible to eradicate all bacteria in the world, humans would notice the effects immediately and, for a while, might find it a favorable change. We would not have to be as careful about preparing and refrigerating foods; plaque would no longer develop on our teeth; and there would be fewer cleaning chores around the house. Quite suddenly, the medical community's goal of eradicating certain infectious diseases, such as tuberculosis, cholera, and tetanus, could be a reality. But there are other considerations to take into account. We would also have to do without certain foods, like sauerkraut, yogurt, Swiss cheese, and sourdough bread. At first, this may seem a small price to pay, but are these slight inconveniences the only sacrifices to be expected? Within a few days, industrial processes that produce vitamins, drugs, and solvents would lie abandoned, and most molecular biology research labs and biotechnology companies would be shut down. In a few months and years, humus containing dead animal and plant matter would build up and trap the very elements needed to sustain the living world. Clearly, bacteria play vital roles in all aspects of our existence. We literally can't live without them!

In order to explore the roles of bacteria in nutrition, genetics, drug therapy, infection, and microbial ecology, we must first understand several aspects of the structure and behavior of procaryotic cells. The primary topics to be covered in this chapter are elements of microscopic anatomy, physiology, identification, and classification and a survey of selected bacterial groups.