Microbial (Bacterial) Nutrition

Bacterial Nutritionis importantfor the optimum growth of the organism because it is the only means by which the organism can acquire all necessary materials required for its cellular biosynthetic activities as well as for the generation of energy (i.e. adenosine triphosphate, ATP). Nutrients are substances 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.

Knowing the nutritional requirements of microorganisms gives microbiologists an understanding of the basic culture media and constituents required successfully cultivate microbes in the microbiology lab 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.

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; and 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 (e.g. Ca, Mg, K and Fe) play various metabolic, enzymatic and regulatory functions in microbial cell.

Micronutrients or microelements 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.

A balance of 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; and they include copper (Cu),  manganese (Mn), cobalt (Co), molybdenum (Mo) and zinc (Zn) which is mainly found in the active site of some important bacterial enzymes (e.g. metallo-beta-lactamases).

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, but equilibrium must be maintained between the macroelements and trace elements together with the 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. 

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. These growth precursors or nutrient constituents which the microorganisms (e.g. bacteria) cannot synthesize on their own but must be obtained from the environment are known as growth factors.

Growth factors are organic compounds that must be supplied in the diet or nutrient of a microbial cell for optimal growth to occur. This is because such growth nutrient requirements (e.g., folic acid) are very essential cell components or precursors of such components and cannot be synthesized by the organism. They cannot be synthesized from available nutrients by microbes; and they include vitamins (e.g. folic acid, biotin,riboflavin and thiamin) which are needed by microbes as coenzymes, amino acids (e.g. alanine and tryptophan) which are basically required for the synthesis of protein molecules and nitrogenous bases (e.g. purines and pyrimidines) which are required by microbes for the synthesis of nucleic acids (i.e. DNA and RNA).

Growth factors as aforesaid 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; and 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. The specific functions of the macroelements and microelements are listed in Table 1.

Table 1. Nutritional requirements of microorganisms

Nutrients	Function
Macronutrients
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 cell.
Phosphorus (P)	Phosphorus is required by microbial cells for the synthesis of phospholipids and nucleic acid, 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.
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 constituent of bacterial cell wall.
Magnesium (Mg+)	Magnesium is required for the metabolic activity of enzymes, ribosomes and nucleic acids.
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.
Micronutrients
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.

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