ENVIRONMENTAL FACTORS

For bacteria to grow and multiply most rapidly, certain requirements must be met. First of this requirement is sufficient food of the proper kind must be present. Then moisture must be available. The temperature must be that most suitable for the species. Likewise, the proper degree of alkalinity or acidity must be present. Another thing to consider is that the oxygen requirements of the species must be met. Light must also be partially or completely excluded. Lastly, the byproducts of bacterial growth must not accumulate in undue amounts. Significant departure from any of these requirements will modify bacterial growth, although bacteria generally possess a greater degree of resistance to unfavorable conditions in the environment than do plants and animals.

Culture media is known as the food materials prepared for the growth of bacteria in the laboratory. It must be noted that some bacteria will grow on practically any properly prepared culture medium. Others grow only on especially nutritious ones, and a few will not grow on any artificial medium. How the bacteria grow in different media can be observed closely with the use of the microscope.

Nutrition

The protoplasm of the bacterial cell is composed of numerous organic compounds, including proteins, fats, and carbohydrates, as well as various inorganic components containing sulfur, phosphorus, calcium, magnesium, potassium, and iron. Proteins comprise about 50% of the dry weight of the cell. It must be mentioned that each species has a type of protein peculiar to itself. Bacterial nitrogen makes up 10%. In some species carbohydrates are plentiful, and important traits of the species depend on these compounds.

Nutrition is the provision of food materials or what we call as chemical substances to bacteria so that they can grow, maintain their constituents, and multiply. For their nourishment bacteria require sources of carbon and nitrogen, growth factors, certain mineral salts, and sources of energy. With the exception of some saprophytic species, all bacteria derive their carbon and nitrogen from organic matter. A number of minerals are required, the most important of the salts being those of calcium, phosphorus, iron, magnesium, potassium, and sodium. Certain minerals are prerequisite to the activation of enzymes.

Many microorganisms can synthesize all the organic compounds of their complex makeup if supplied with the basic nutrients. Many cannot, however, since they require vitamins and certain organic growth factors since growth factor is utilized as the intact substance for their activities. In this respect microorganisms resemble rather closely higher forms of life. In fact, such vitamins as nicotinic acid, pantothenic acid, and para - aminobenzoic acid, biotin, and folic acid requirements for animal nutrition-were first studied and identified as substances necessary for the growth of microorganisms.

KINDS OF ORGANISMS

Organisms can be classified according to how they obtain their nourishment. Saprophytes are organisms that obtain their nourishment from nonliving organic material. Those that depend on living matter for their sustenance are known as parasites. Facultative saprophytes usually obtain nourishment from living matter but may obtain it from dead organic matter. Facultative parasites on the other hand usually obtain nourishment from dead organic matter but may obtain it from living matter. Some pathogenic bacteria can exist only on living material. For instance the spirochete of syphilis cannot be grown outside a living organism. Most, however, can lead either a parasitic or a saprophytic existence. A few pathogenic bacteria, usually saprophytic, may adapt themselves to a parasitic existence. The best example for this is the bacteria that cause gas gangrene. The organism on which a parasite lives is known as a host.

Organisms that obtain their nutriments by breaking down organic matter into simpler chemical substances are heterotrophic or organotrophic. Those that obtain them by building the organic compounds in protoplasm from the simpler inorganic substances are autotrophic or lithotrophic. All pathogenic bacteria and many nonpathogenic ones are heterotrophic. The different types of organisms can be studied more accurately under the microscope.