Chapter Capsule

I. Microbiology is the study of bacteria, viruses, fungi, protozoa, and algae, which are collectively called microorganisms, or microbes. In general, microorganisms are microscopic and, unlike macroscopic organisms, which are readily visible, they require magnification to be adequately observed or studied.

II. Microbes live in most of the world’s habitats and are indispensable for normal, balanced life on earth. They play many roles in the functioning of the earth’s ecosystems. Most organisms are free-living, but a few are parasites.

A. Microbes are involved in nutrient production and energy flow. Algae and certain bacteria trap the sun’s energy to produce food through photosynthesis.
B. Other microbes are responsible for the breakdown and recycling of nutrients through decomposition. Microbes are essential to the maintenance of the air, soil, and water.

III. Microbes have been called upon to solve environmental, agricultural, and medical problems.

A. Biotechnology applies the power of microbes toward the manufacture of industrial products, foods, and drugs.
B. Microbes form the basis of genetic engineering and recombinant DNA technology, which alter genetic material to produce new products and modified life forms.
C. With bioremediation, microbes are used to clean up pollutants and wastes in natural environments.

IV. Nearly 2,000 microbes are pathogens that cause infectious diseases. Infectious diseases result in high levels of mortality and morbidity. Many infections are emerging, meaning that they are newly identified pathogens gaining greater prominence. Many older diseases are also increasing.

V. The simplicity, growth rate, and adaptability of microbes are some of the reasons that microbiology is so diverse and has branched out into many subsciences and applications. Important subsciences include immunology, epidemiology, public health, food, dairy, aquatic, and industrial microbiology.

VI. Important Historical Events

A. Microbiology as a science is about 200 years old. Hundreds of contributors have provided discoveries and knowledge to enrich our understanding.
B. With his simple microscope, Leeuwenhoek discovered organisms he called animalcules. As a consequence of his findings and the rise of the scientific method, the notion of spontaneous generation, or abiogenesis, was eventually abandoned for biogenesis. The scientific method applies inductive and deductive reasoning to develop rational hypotheses and theories that can be tested. Principles that withstand repeated scrutiny become law in time.
C. Early microbiology blossomed with the conceptual developments of sterilization, aseptic techniques, and the germ theory of disease.

VII. Characteristics and Classification of Microorganisms

A. Organisms can be described according to their morphology and physiology. The genetics of organisms reveals an ancestral evolutionary relationship among these kingdoms.
B. Cells of eucaryotic organisms contain a nucleus, but those of procaryotic organisms do not.
C. Taxonomy is a hierarchy scheme for the classification, identification, and nomenclature of organisms, which are grouped in categories called taxa, based on features ranging from general to specific.
1. Starting with the broadest category, the taxa are domain, kingdom, phylum (or division), class, order, family, genus, and species. Organisms are assigned binomial scientific names consisting of their genus and species names.
2. The latest classification scheme for living things is based on the genetic structure of their ribosomes. The Woese-Fox system recognizes three domains: Archaea, simple procaryotes that live in extremes; Bacteria, typical procaryotes; and Eukarya, all types of eucaryotic organisms.
3. An alternative classification scheme uses a simpler five-kingdom organization: Kingdom Procaryotae (Monera), containing the eubacteria and the archaebacteria; Kingdom Protista, containing primitive unicellular microbes such as algae and protozoa; Kingdom Myceteae, containing the fungi; Kingdom Animalia, containing animals; and Kingdom Plantae, containing plants.

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