Microbial Physiology: Culture Media & Microorganisms - PDF

Okay, here is the conversion of the supplied text into markdown format. # Microbial physiology Microorganisms are a diverse group of organisms, including bacteria, actinomycetes, fungi, and cyanobacteria, and have interesting characteristics. Most microorganisms lack chlorophyll, except for cyanob...

Okay, here is the conversion of the supplied text into markdown format. # Microbial physiology Microorganisms are a diverse group of organisms, including bacteria, actinomycetes, fungi, and cyanobacteria, and have interesting characteristics. Most microorganisms lack chlorophyll, except for cyanobacteria and phototrophic bacteria, which derive energy from light. Heterotrophic microorganisms (lacking chlorophyll) depend on external sources for their nutritional requirements. If they obtain nutrients from living host cells, they are known as parasites; otherwise, they are known as saprophytes if they obtain their nutritional requirements from organic matter or dead materials. Microbial physiology is a branch of biology that deals with microbial activities and functions, how they affect their environment, and how the environment affects them. ## Culture media For any microorganism to be propagated, it is necessary to provide the appropriate biochemical and biophysical environment. Heterotrophs utilize the surrounding material to maintain growth, synthesis of protoplasm, cellular constituents, and other activities. Most essential elements, such as K, Mg, P, and S, are taken up as ions. However, other organic compounds, such as vitamins, are utilized as such from the media by vitamin-deficient microorganisms. Culture media are employed in the isolation, maintenance, and identification of microorganisms. Liquid media are used for biomass production as well as physiological studies of microorganisms, while solidified media are used for isolation of pure cultures, morphological studies, and a variety of other purposes. ### Types of culture media: Culture media may be classified into several categories depending on their composition or use. #### 1. Natural media: A complex medium is one in which the exact chemical constitution of the medium is not known. Complex media usually contain complex materials of biological origin, such as blood, milk, yeast extract, beef extract, or plant extracts, the exact chemical composition of which is obviously undetermined. Complex media are usually used for the isolation of microorganisms and studying their morphological characteristics, especially when used in the solidified state. Complex media usually provide the full range of growth factors that may be required by an organism. #### 2. Semisynthetic medium: These media contain some constituents of defined chemical composition, while others are derived from complex sources with unknown composition. This type of media may be useful in microbial isolation. Potato-dextrose agar is one of the popular semi synthetic media. #### 3. Synthetic (defined) medium: A chemically defined medium is one in which the exact chemical composition is known. Chemically-defined media are useful in studying the minimal nutritional requirements of microorganisms, for enrichment cultures, and for a wide variety of physiological studies. Growth and reproduction are frequently less on a synthetic medium than on one containing complex materials. Addition of 20 mg/L of either peptone or yeast extract resulted in improvement of growth and decreasing the time required for sporulation. Other concepts employed in the construction of culture media are the principles of selection and enrichment. A selective medium is one that has a component(s) added to it that will inhibit or prevent the growth of certain types or species of microorganisms (especially in the case of bacteria) and/or promote the growth of the desired species. Temperature and pH can also be adjusted to render the medium selective for organisms. Differential medium may allow the microbiologist to distinguish between different types of bacteria. For example, *Staphylococcus aureus* (common bacterial pathogen) can be isolated and identified by differential medium containing a very high concentration of salt, mannitol as a fermentable sugar, and a pH indicator dye. Mannitol-fermenting colonies (*S. aureus*) produce acid and react with the dye, forming a colored halo around the colonies. On the other hand, mannitol non-fermenters (*S. epidermidis*, non-pathogenic) do not form a halo around their colonies.