Tiêu đề 4. NUTRITIONAL REQUIREMENTS, GROWTH AND CULTIVATION OF BACTERIA.pdf ✅

PHARMD GURU Page 1 INTRODUCTION: BACTERIA (AEROBIC & ANAEROBIC):  Bacteria can grow in the variety of media which provide a source of energy and basic nutrients that include carbon, nitrogen, phosphorous, oxygen, hydrogen and sulfur.  There are several environmental factors include temperature, pH, oxygen requirement and, osmotic pressure that control the growth of the microorganisms.  The term growth is commonly applied for biological cell usually refers to changes in the total population rather than an increase in the size of an individual organism.  Prokaryote growth is exponential as cells divide by binary fission.  The time required to double the population of cell (generation time), depends on the growth rate of organism, media composition and environmental conditions.  Escherichia coli can grow with a doubling time of approximately 20 min.  Bacterial growth in liquid medium follows a typical pattern often called the bacterial growth curve. Continuous bacterial growth can be maintained by adding fresh medium continuously in culture vessel.  The number of cells in a culture can be estimated by counting individual cells, diluting and inoculating the culture on solid medium, measuring the light scattered by a culture, weighing wet or dried cells and using biochemical methods to measure cell components. FUNGI:  Fungi are a group of non-motile eukaryotic organisms which exist as saprophytes, parasites or commensals.  They possess differentiated nuclei surrounded by a nuclear membrane and reproduced either by budding or by forming spores.  They have rigid chitinous cell walls. Morphologically, fungi may be either simple oval cells or long tubular septate hyphae showing true lateral branching. NUTRITIONAL REQUIREMENTS, GROWTH AND CULTIVATION OF BACTERIA
PHARMD GURU Page 2  All fungi are chemohetrotrophs, requiring organic compounds for energy and carbon. Fungi are aerobic or facultative anaerobic.  The majority of fungi are saprophytes in soil and water.  They divide asexually, sexually or by both processes. They may be unicellular or multicellular. VIRUSES:  Viruses are infectious agents so small that they can only be seen at magnifications provided by the electron microscope.  They are 10 to 100 times smaller than most bacteria (20 to 300 nm).  Viruses are incapable of independent growth in artificial media. They can grow only in animal or plant cells or in microorganisms. Thus, viruses are referred to as obligate intracellular parasites.  Viruses largely lack metabolic machinery of their own to generate energy or synthesize proteins.  They depend on the host cells to carry out these vital functions. GROWTH AND CULTIVATION OF BACTERIA: Bacteria required adequate nutrition, optimum pH, temperature and oxygen for growth and multiplication. Suitable artificial media containing sources of carbon, nitrogen, hydrogen, oxygen, phosphorous and other elements such as sodium, potassium, magnesium and iron in very small amounts have been used for cultivation of micro-organisms in the laboratory. Bacteria can be classified depending on nutritional requirements (Fig. 3.1) i.e. sources of energy, electron, carbon etc. 1. Source of energy: Bacteria which derive their energy from sunlight are called phototrophs (e.g. Rhodospirillum rubrum) and those that obtain energy from chemical reactions are called chemotrophs (e.g. Escherichia coli). 2. Source of electrons: All micro-organisms require a source of electrons for their metabolism. Bacteria which use reduced inorganic compounds as electron donors are called lithotrophs (e.g. Pseudomonas pseudoflava) and some other species which use organic compounds as electron donors are called organotrophs (e.g. Escherichia coli).
PHARMD GURU Page 3 Among the phototrophic bacteria, some species use inorganic compounds (H2S) as source of electrons and are called photolithotrophs (e.g. Chromatium okenii) and others which use organic compounds such as fatty acids and alcohols as electron donors are called photoorganotrophs (e.g. Rhodospirillum rubrum). Among the chemotrophic bacteria, some species use inorganic compounds as the source of electrons and are called chemolithotrophs (e.g. Nitrosomonas europaea) and others use organic compounds such as sugar and amino acids as electron donors and are called chemoorganotrophs (e.g. Escherichia coli). 3. Source of carbon: Microorganism require carbon for synthesizing cell components. However, some species use CO2 as the major source of carbon. These microorganisms are called autotrophs (e.g. Chromatium okenii). Other species require organic compounds as a source of carbon, such species are called heterotrops (e.g. Escherichia coli). 4. Nitrogen: Bacteria can use nitrogen from the atmosphere or from inorganic compounds such as nitrates, nitrites, ammonium salts or organic compounds such as amino acids. Nitrogen is a major component of protein and nucleic acids. 5. Sulphur: Many bacterial species use sulphur from organic sulphur compounds, inorganic sulphur compounds and elemental sulphur. Sulphur is needed for synthesis of amino acids (e.g. cystine, methionine etc.).
PHARMD GURU Page 4 6. Phosphorus: Phosphorus, usually supplied in the form of phosphate is an essential component of nucleotides, nucleic acids, phospholipids etc. 7. Mineral salts: Bacteria require salts, particularly the anions such as phosphate and sulphate and the cations as sodium, potassium, magnesium, iron and calcium. These are normally present in the natural environments or may be added in culture media. 8. Growth factors or bacterial vitamins: Some bacterial species require organic compounds in minute quantities for growth. These are known as growth factors or bacterial vitamins. Some bacteria are capable of synthesizing their entire requirement of vitamins from culture medium. Some other species cannot synthesize the vitamins from media and do not show growth in the absence of vitamins. Hence, for the growth of these species (Table 3.1), vitamins are added in the culture media. 9. Water: It is the major essential nutrient as it accounts for about 80 to 90% of the total weight of cells. Water is a highly polar compound and it contains micronutrients and trace elements which are required for the growth of bacteria.