Microbiology is the science that studies micro-organisms and viruses. Micro-organisms are too small to be distinguished by the naked eye (ie, less than 0.1 mm in diameter); hence, their discovery and study occurred only after the introduction of adequate microscopes. These organisms have in common a relatively simple cell structure, although different species may differ in some aspects of their structure. Based on structural aspects, particularly those of the nucleus, micro-organisms are divided into 2 groups, eukaryotes (having a true, membrane-bound nucleus) and prokaryotes (with a primitive nucleus).

Protozoa, fungi and most algae are eukaryotic, as are the cells of higher plants and animals. Bacteria and the Archaebacteria (Archaea) are the only prokaryotes. Because viruses require host cells to perform their life processes, they are in a class by themselves, being neither eukaryotic nor prokaryotic.

Micro-organisms are of interest, in part, because some varieties cause disease. However, micro-organisms exist in all habitats and are an important component of all normal ecosystems. Soil and the oceans are the most important habitats. Soil supports a wide range of types and, as it is a very stable habitat, protects them for months or years. Micro-organisms decompose organic matter (plant and animal remains, sewage, etc) to simple molecules that can be used by plants, and oxidize or reduce insoluble elements (eg, sulphur) to soluble compounds also usable as plant food. Even pesticides and petroleum products will be broken down to less dangerous forms.

The oceans are low in nutrients and over 80% of ocean water is below 4°C; hence the microbial population and rate of growth and metabolism are very low. However, ocean bacteria can grow, albeit slowly, at these temperatures. These bacteria require sodium as a nutrient and some (called barophiles) require great pressures.

Marine micro-organisms function like terrestrial ones in decomposing organic matter and converting it to forms available to aquatic plants. For example, a relatively small number of petroleum-decomposing bacteria occur in the oceans, limited by the low level of nutrients. When an oil spill provides an abundant carbon source, the bacterial population increases immediately, provided that enough nitrogen and phosphorus are also present. In the long run, substances that cannot be handled by micro-organisms (eg, heavy metals, some pesticides, thermal pollution) will become the most serious pollution problems. In addition, phytoplankton (photosynthetic algae and some protozoa) form critical links in ocean food chains.

On the negative side, the many disease-causing micro-organisms are undesirable in themselves. Furthermore, micro-organisms cause disease in plants, and constant effort is required to breed disease-resistant (eg, rust-resistant) varieties, especially as the fungi that cause rusts and many other plant diseases continually evolve new ways of attacking plants. Micro-organisms contribute to pollution by oxidizing organic matter, thus using up available oxygen and causing the death of fish and other oxygen-requiring organisms.

Bacteria can cause problems in water systems by oxidizing iron or manganese to insoluble salts that clog pipes. Some bacteria, in the absence of oxygen, will reduce sulphate to hydrogen sulphide, a weak acid that corrodes metal pipes. Crude oil is often very high in sulphur, and bacteria capable of oxidizing sulphur to sulphuric acid are present in oil wells. The acid formed destroys drilling bits and shafts.

Uses of Microbiology

In industrial societies, micro-organisms are put to a variety of uses to enhance the quality of the human environment.

Sewage Treatment

Micro-organisms, particularly bacteria, play a major role in sewage treatment. They oxidize organic matter present in waste water to its basic constituents and thus reduce potential harmful effects on fish and other oxygen-requiring organisms. The first microbiological step of sewage treatment, carried out in the absence of oxygen, produces methane gas. Many sewage plants get all their energy from this source. To complete decomposition, aeration is required and is accomplished in various ways. Aeration has the added effect of killing undesirable bacteria.

Industrial Microbiology

The dairy industry has a long history of work with micro-organisms. Pasteurization of milk was introduced soon after 1886 to kill pathogenic bacteria and generally reduce bacterial numbers, thereby increasing the keeping quality of milk. Yogurt, cottage cheese, buttermilk and acidophilus milk are produced by controlling fermentation of milk by various lactic acid bacteria (especially the Lactobacilli). Various strains of yeast have been developed that produce ethyl alcohol and flavour compounds from grapes, and are tolerant of high concentrations of alcohol. These yeasts are the basis of the wine industry. Problems arise when wild yeasts take over fermentation. Wine must also be protected from bacterial contamination because bacteria may form lactic acid or oxidize alcohol to vinegar.

Brewing also uses yeast to convert sugar to alcohol. In this case, the source of sugar is cereal grain and the yeast does not have to be tolerant of high levels of alcohol. Bottled or canned beer is pasteurized in the container to prevent bacterial attack; keg beer is not pasteurized but relies on refrigeration and rapid use for its desirable qualities. Distilleries use yeast fermentation of grains, molasses, fruits and vegetables to obtain alcohol which is then distilled from the mash, aged and blended.

One of the major industrial uses of micro-organisms is in the production of antibiotics. Penicillin, the first to be discovered, is still the most widely used. Antibiotics act by interfering with the normal metabolic processes of bacteria or other micro-organisms. Thus, penicillin interferes with the synthesis of the cell wall of prokaryotic cells. This cell wall is totally unlike the wall in any eukaryote; hence, penicillin is selective for bacteria and blue-green algae. Over 100 antibiotics are now in use and more than 5000 different types have been produced. In general, the useful antibiotics are produced by fungi and by a special group of bacteria known as the Streptomyces.

To an ever-increasing degree, micro-organisms are being used to produce industrial enzymes (complex proteins that catalyze specific reactions). Bacteria, especially, are capable of secreting enzymes from their cells, thus making it much simpler to concentrate and purify the enzyme. The greatest industrial use of enzymes is in the chill proofing of beer; ie, in making the proteins and carbohydrates soluble so that they do not precipitate when the beer is chilled. Microbial enzymes are also used to remove the bitter constituents of grapefruit peel in juice production and to convert glucose (corn sugar) to the much sweeter sugar fructose. The enzyme rennin, used to coagulate milk for cheese making, is now largely obtained from fungi. Single-cell proteins, used primarily for animal feed, are produced using micro-organisms.

Micro-organisms are also used in such industrial processes as the synthesis of methane from cellulose (eg, from pulp and paper industry wastes); the process is still largely experimental (see Biomass Energy). Bacteria may be used to dissolve metals from ores, a procedure widely practised in the Canadian mining industry.

Microbiology in Canada

Microbiology is a strong science in Canadian universities. In many instances, it is centred in medical schools, but there are successful departments in faculties of science or agriculture. The National Research Council, Agriculture Canada and the Dept of Fisheries and Oceans have a long tradition of research in microbiology. Microbiology is more widely accepted as a profession than are other biological sciences. There are all levels of employment for graduates in hospitals, public health laboratories and private diagnostic laboratories. Within the food and beverage industries, dairying is the chief employer, although breweries, wineries and meat-packing plants routinely employ microbiologists for quality control work. The training is also considered appropriate for a brewmaster or wine maker.

In many industries, a microbiology background is considered an excellent preparation for a management position. Universities are one of the largest employers of the most highly trained individuals (in research and teaching) and of those with a BSc degree (eg, laboratory demonstrators, research assistants). The pharmaceutical industry employs graduates either in sales or in their research or quality control laboratories.

In Canada, microbiologists may belong to the professional associations: Canadian Society of Microbiologists, Canadian Assn of Medical Microbiologists, Canadian Assn of Clinical Microbiology and Infectious Diseases, Canadian Genetics Society, Canadian Society for Cell Biology, Canadian Biochemical Society, Canadian Society of Immunology, Canadian Assn of Public Health, Canadian Society of Clinical Chemists and the Canadian College of Microbiologists.


Soils are often deficient in nitrogen and, although nitrogen-fixing strains of bacteria are present in soil, they may not occur in high enough numbers to be effective. To safeguard against this possibility, the seeds of legumes (eg, clover, peas, beans) are often preinoculated with the appropriate nitrogen-fixing bacteria. As the seeds germinate and plants grow, the bacteria (genus Rhizobium) invade the roots and concentrate in nodules on them. The plant supplies energy from the sun and the bacteria convert nitrogen to ammonia to feed the plant and enrich the soil. There is also some advantage to inoculating nitrogen-poor soils with free-living nitrogen-fixing bacteria of the genus Azotobacter. Micro-organisms have also been used to control insect pests that attack plants (eg, spruce budworm and sawflies).

In Biotechnology, a field now attracting a great deal of attention, characteristics from several strains of organisms are combined into a single cell, usually a bacterium. The basic techniques are those of microbial genetics. The production of compounds (eg, insulin, interferon) by bacteria is already underway, and the potential for the production of important biological compounds is very great.