Bacterial nutrition is important for the optimum growth of the organism because it is one of the major means by which the organism can acquire all necessary materials required for its cellular biosynthetic activities as well as for the generation of energy (for example, adenosine triphosphate, ATP) required for unperturbed survival in its habitat or niche. These materials required for the unperturbed growth of the organism may be regarded as nutrients. In this case therefore, nutrientsare substances (organic and inorganic) required for energy production and other biosynthetic activity necessary for the unperturbed growth of microorganisms. They are substances that can be taken up by microorganisms in their natural environment and metabolized to provide energy and other precursors for biosynthetic reactions in the microbial cell. There abound several nutritional requirements or nutrients in the natural environment of microorganisms; and these are judiciously accessed and utilized by microbes to facilitate their proliferation in the environment. However, microorganisms can be harvested from their natural environment and cultured or grown in vitro (i.e., in artificial medium); and all nutritional requirements as is available in their natural habitat must be provided to ensure optimum growth of the organism. The nutrients supplied in growth or culture media must contain the necessary constituents necessary for the propagation of the cultivated organism; and these nutrients usually mimic those biological, chemical and physical factors found in the organism’s natural habitat or niche.
Knowing the nutritional requirements of microorganisms gives microbiologists an understanding of the basic culture media and constituents required to successfully cultivate microbes in the microbiology laboratory as well as to recover same from their natural environment. For optimum growth to take place, microbial cells require some key nutrients in the right amount to grow effectively. The nutrients required by microbial cells for growth can be either macronutrients or micronutrients. These nutrients are required by microbes in different proportions and they are mainly used for the production of proteins, carbohydrates, nucleic acids, lipids, energy and other important growth factors needed for the optimal growth of the organism being cultivated.
MACRONUTRIENTS, MICRONUTRIENTS AND GROWTH FACTORS
Macronutrients or macroelements are those nutrients required by microorganisms in relatively large amounts; and they include carbon (C), nitrogen (N), oxygen (O), sulphur (S), hydrogen (H), iron (Fe), phosphorus (P), calcium (Ca), potassium (K) and magnesium (Mg). Nutritional factors significantly influence the actual growth of a microbial cell especially if these nutritional requirements are not found in the right amount and/or concentration in the organism’s growth vessel (in vitro) or its natural environment. Macroelements (which are required in large amount for microbial growth) could adversely affect the optimum growth of an organism when they are lacking in their correct proportion. Macroelements as exemplified above are important for the synthesis of nucleic acids, lipids, proteins and other important molecules in the microbial cell. Some of these elements (for example, Ca, Mg, K and Fe) play various metabolic, enzymatic and regulatory functions in microbial cell. Their absence might negatively affect the optimal growth of the microbe.
Micronutrients or microelements on the other hand are nutrient molecules required by microorganisms in relatively small amounts. That they are required in small amounts by microbes than are macroelements (which are required in large amounts) does not make them any less important to the nutritional requirements of microorganisms. However, a balance of both micronutrients and macronutrients in the growth or culture media of microorganisms is vital for optimum growth of the organism. Generally known as trace elements, micronutrients majorly make up enzymes and cofactors of microbes. Micronutrients include copper (Cu), manganese (Mn), cobalt (Co), molybdenum (Mo) and zinc (Zn). Zinc (Zn) for example, is mainly found in the active site of some important bacterial enzymes including those that aids the organism’s pathogenesis. Micronutrients play several regulatory and catalytic roles in microbial cells. The successful cultivation of microorganisms is also dependent on several environmental factors including oxygen concentration, moisture content, temperature, pH and osmotic concentration. However, equilibrium must be maintained between the macroelements and trace elements together with these environmental factors for microbial growth to occur at an optimum level. Thus, for optimal microbial growth and yield of secondary or primary metabolites, microorganisms must be supplied with the requisite amount of nutritional supplements required for the finest growth to take place, and other environmental conditions must also be monitored and controlled in the growth process as well. The specific functions of the macroelements and microelements are listed in Table 1.
Microorganisms elaborate several metabolic pathways which allow them to synthesize some of the basic nutrients they require for growth. However, there are some nutrients important for growth and which the organisms cannot produce or synthesize on their own because they lack the enzymatic machinery required for their synthesis.
Table 1. Nutritional requirements of microorganisms
|Nitrogen (N)||Nitrogen is required for the synthesis of enzymes, nucleotides and amino acids.|
|Carbon (C)||Carbon is among the constituents of the cellular material of microbial cells.|
|Sulphur (S)||Sulphur is required for the synthesis of amino acids, and it is also a constituent of microbial coenzymes.|
|Hydrogen (H)||Hydrogen is a constituent of microbial organic compounds and the cytosol or cell water of the microbial cell.|
|Phosphorus (P)||Phosphorus is required by microbial cells for the synthesis of phospholipids and nucleic acid molecules, and it is also a constituent of microbial teichoic acid and lipopolysaccharide (LPS).|
|Oxygen (O)||Oxygen play vital role in the electron transport chain of the cell (as an electron acceptor in aerobic organisms); and it makes up the cell water of microbial cells.|
|Potassium (K+)||Potassium is required for protein synthesis; and it is a cofactor for many microbial enzymes.|
|Calcium (Ca+)||Calcium play vital role in the heat stability of bacterial endospores; and they also act as cofactor for some bacterial enzymes. They are constituents of bacterial cell wall.|
|Magnesium (Mg+)||Magnesium is required for the metabolic activity of enzymes, ribosomes and nucleic acid molecules.|
|Iron (Fe+)||Iron is important for electron transport reactions in the cell; and they are important components of cytochromes. They also serve as cofactors for some enzymes.|
|Zinc (Zn)||Zinc is an important cofactor for the active site of some bacterial enzymes. Generally, all trace elements usually act as cofactors for some microbial enzymatic reactions even though they are required in very small amounts by microbes for growth.|
|Manganese (Mn)||Same as above.|
|Cobalt (Co)||Same as above.|
|Copper (Cu)||Same as above.|
|Molybdenum (Mo)||Same as above.|
These growth precursors or nutrient constituents which the microorganisms (for example, bacteria) cannot synthesize on their own but must be obtained from the environment are known as growth factors. They cannot be synthesized from available nutrients by microbes. These additional growth factors required for microbial growth include vitamins (for example, folic acid, biotin,riboflavin and thiamin) which are needed by microbes as coenzymes; amino acids (for example, alanine and tryptophan) which are basically required for the synthesis of protein molecules; and nitrogenous bases (for example, purines and pyrimidines) which are required by microbes for the synthesis of nucleic acids (i.e., DNA and RNA). Growth factors are organic substances that must be supplied in nutrient compositions required for microbial growth. They are basically found in culture or growth media in different amount. Growth factors (i.e., vitamins, amino acids and the nitrogenous bases) are obtained and metabolized by microorganisms from their immediate environment once supplied in the growth medium.
Brooks G.F., Butel J.S and Morse S.A (2004). Medical Microbiology, 23rd edition. McGraw Hill Publishers. USA.
Gilligan P.H, Shapiro D.S and Miller M.B (2014). Cases in Medical Microbiology and Infectious Diseases. Third edition. American Society of Microbiology Press, USA.
Madigan M.T., Martinko J.M., Dunlap P.V and Clark D.P (2009). Brock Biology of Microorganisms, 12th edition. Pearson Benjamin Cummings Inc, USA.
Mahon C. R, Lehman D.C and Manuselis G (2011). Textbook of Diagnostic Microbiology. Fourth edition. Saunders Publishers, USA.
Patrick R. Murray, Ellen Jo Baron, James H. Jorgensen, Marie Louise Landry, Michael A. Pfaller (2007). Manual of Clinical Microbiology, 9th ed.: American Society for Microbiology.
Wilson B. A, Salyers A.A, Whitt D.D and Winkler M.E (2011). Bacterial Pathogenesis: A molecular Approach. Third edition. American Society of Microbiology Press, USA.
Woods GL and Washington JA (1995). The Clinician and the Microbiology Laboratory. Mandell GL, Bennett JE, Dolin R (eds): Principles and Practice of Infectious Diseases. 4th ed. Churchill Livingstone, New York.