Methods of studying microorganisms

Except for certain studies where bacterial populations are examined in their natural habitats, bacteria are usually cultivated and studied under   laboratory conditions. Numerous media (singular, medium) have been developed for bacterial cultivation. Because the nutritional requirements of bacteria vary widely, there are great differences in the chemical compositions of the media used in the laboratory. Bacteria also exhibit wide differences with respect to the physical conditions favoring their growth, such as temperature, pH and gaseous environment.

The successful cultivation of bacteria requires an awareness of all of these factors.

• Nutritional requirements
• All forms of life, from microorganisms to human beings, share certain nutritional requirements
• for growth and normal functioning.

1. All organisms require a source of energy. Some rely on chemical compounds for their energy and are designated as chemotrophs. Others can utilize radiant energy (light) and are called phototrophs. Both chemotrophs and phototrophs exist among bacteria.

2. All organisms require a source of electrons for their metabolism. Some organisms can use reduced inorganic compounds as electron donors and are termed lithotrophs (some may be chemolithotrophs other photolithotrophs). Other organisms use organic compounds as electron donors and are called organotrophs.

3. All organisms require carbon in some form for use in synthesizing cell components. All organisms require at least small amounts of CO2. However, some can use CO2 as their major, 3 or even sole, source of carbon; such organisms are termed autotrophs. Others require organic compounds as their carbon source and are termed heterotrophs.

4. All organisms require nitrogen in some form for cell components. Bacteria are extremely versatile in this respect. Unlike eucaryotes, some bacteria can use atmospheric nitrogen. Others thrive on inorganic nitrogen compounds such as nitrates, nitrites, or ammonium salts, and still others derive nitrogen from organic compounds such as amino acids.

5. All organisms require oxygen, sulfur and phosphorous for cell components. Oxygen is provided in various forms, such as water; component atoms of various nutrients; or molecular oxygen. Sulfur is needed for synthesis of certain amino acids (cysteine, cystine and methionine). Some bacteria require organic sulfur compounds, some are capable of utilizing inorganic sulfur compounds, and some can even use elemental sulfur. Phosphorous, usually supplied in the form of phosphate, is an essential component of nucleotides, nucleic acids, phospholipids, teichoic acids, and other compounds.

6. All living organisms require metal ions, such as K +, Ca2+, Mg2+ and Fe2+ for normal growth. Other metal ions are also needed but usually only at very low concentrations,  such as Zn2+Cu2+, Mn2+, Mo6+, Ni2+, and Co2+; these are added in trace quantity in culture media which is sufficient to support bacterial growth. Not all the biological functions of metal ions are known, but Fe2+ , Mg2+, Zn2+Mo6+, Mn2+and Cu2+ are known to be cofactors for various enzymes. Most bacteria