Microbial Nutrition
Some of the elements found in large amounts within the cell are carbon, nitrogen, oxygen, hydrogen, sulfur, and phosphorous. These elements are considered macronutrients and make up carbohydrates, proteins, lipids, and nucleic acids. Other elements such as calcium, potassium, magnesium, and iron are used in electron transfers, as cofactors, and as part of larger complexes. Micronutrients are trace elements that are not prominent within the cell and are used for maintenance and help catalyze reactions.
Microorganisms have different mechanisms in which they utilize food and energy sources as well as different needs for specific nutrients. Nutrient sources available to one organism may not be necessarily available to another. Autotrophs can only use carbon dioxide as a principle carbon source. Many are photosynthetic and some are capable of utilizing inorganic compounds. Heterotrophs use organic molecules as a source of carbon and energy. The type of organic carbon used is dependent on the microorganism and its metabolic system.
Nitrogenous compounds such as amino acids, ammonia, nitrate, and atmospheric nitrogen provide the cell with nitrogen for the production of amino acids, nitrogenous bases, carbohydrates, lipids, and other compounds. Inorganic phosphate is often used to provide phosphorous for compounds such as nucleic acids, nucleotides, and phospholipids. Sulfate and cysteine are common sources of sulfur for use in amino acids, carbohydrates, biotin, and thiamine. Essential compounds that cannot be synthesized such as vitamins are called growth factors.
Culture Media
A culture medium is often used to grow and maintain microorganisms. Some media are used to isolate and/or identify microorganisms and thus require a working knowledge of the normal environment for the organism of interest. A defined medium is a medium in which all the components are known. This type of medium is often used in research. A complex medium contains some ingredients of unknown composition and may work well if the actual growth requirements are unknown. Complex media often include peptones, meat extract, and/or yeast extract in their ingredients. Nutrient broth and tryptic soy broth are some examples of complex media. A selective medium favors the growth of a specific microorganism through the addition of chemicals that are inhibitory to other organisms. A differential medium allows different bacterial groups to be distinguished from one another and provides the means for identification.