Microbial nutrient requirements refers to the chemicals and elements utilized by bacteria for growth, called nutrients. Bacteria require macroelements like carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, potassium, calcium, magnesium, and iron which make up over 95% of bacterial cell dry weight. They also require micronutrients like manganese, zinc, cobalt, molybdenum, nickel, and copper in smaller amounts. A balanced mixture of all required nutrients is necessary for bacterial growth, as a shortage of any essential nutrient will limit growth.

1. Microbial nutrient requirements
By
Mr. K. VIJAY,
Assistant Professor,
Sacred Heart College,
Tirupattur District.

2. Every organism must find in its environment all of the
substances required for energy generation and cellular
biosynthesis.
The chemicals and elements of this environment that are
utilized for bacterial growth are referred to as nutrients or
nutritional requirements.
Many bacteria can be grown the laboratory in culture media
which are designed to provide all the essential nutrients in
solution for bacterial growth.
Bacteria that are symbionts or obligate intracellular parasites
of other cells, usually eukaryotic cells, are (not unexpectedly)
difficult to grow outside of their natural host cells. Whether
the microbe is a mutualist or parasite, the host cell must
ultimately provide the nutritional requirements of its resident.

3. Analysis of microbial cell composition shows that over
95% of cell dry weight is made up of a few major
elements: carbon, oxygen, hydrogen, nitrogen,
sulfur, phosphorus, potassium, calcium,
magnesium, and iron.
These are called macroelements or macronutrients
because they are required by microorganisms in
relatively large amounts. The first six (C, O, H, N, S, and
P) are components of carbohydrates, lipids, proteins,
and nucleic acids.
The remaining four macroelements exist in the cell as
cations and play a variety of roles.

5. For example, potassium (K+) is required for activity by a
number of enzymes, including some of those involved in
protein synthesis.
Calcium (Ca+2), among other functions, contributes to
the heat resistance of bacterial endospores.
Magnesium (Mg+2) serves as a cofactor for many
enzymes, complexes with ATP, and stabilizes ribosomes
and cell membranes.
Iron (Fe+2 and Fe+3) is a part of cytochromes and a
cofactor for enzymes and electron-carrying proteins.

6. All organisms, including microorganisms, require several
micronutrients or trace elements besides
macroelements.
The micronutrients - manganese, zinc, cobalt,
molybdenum, nickel, and copper—are needed by most
cells. However, cells require such small amounts that
contaminants in water, glassware, and regular media
components often are adequate for growth.
Therefore it is very difficult to demonstrate a
micronutrient requirement.
In nature, micronutrients are ubiquitous and probably do
not usually limit growth.

7. Micronutrients are normally a part of enzymes and
cofactors, and they aid in the catalysis of reactions and
maintenance of protein structure.
For example, zinc (Zn+2) is present at the active site of
some enzymes but is also involved in the association of
regulatory and catalytic subunits in E. coli aspartate
carbamoyltransferase.
Manganese (Mn+2) aids many enzymes catalyzing the
transfer of phosphate groups.
Molybdenum (Mo+2) is required for nitrogen fixation, and
cobalt (Co+2) is a component of vitamin B12.

8. Besides the common macroelements and trace
elements, microorganisms may have particular
requirements that reflect the special nature of their
morphology or environment.
Diatoms need silicic acid (H4SiO4) to construct their
beautiful cell walls of silica [(SiO2)n]. Although most
bacteria do not require large amounts of sodium, many
bacteria growing in saline lakes and oceans depend on
the presence of high concentrations of sodium ion (Na).
It must be emphasized that microorganisms require a
balanced mixture of nutrients. If an essential nutrient is
in short supply, microbial growth will be limited
regardless of the concentrations of other nutrients.

9. Element % of dry weight Source Function
Carbon 50
organic
compounds or CO2
Main constituent
of cellular material
Oxygen 20
H2O, organic
compounds, CO2,
and O2
Constituent of cell
material and cell
water; O2 is
electron acceptor
in aerobic
respiration
Nitrogen 14
NH3, NO3, organic
compounds, N2
Constituent of
amino acids,
nucleic acids
nucleotides, and
coenzymes
Hydrogen 8
H2O, organic
compounds, H2
Main constituent
of organic
compounds and
cell water

10. Element % of dry weight Source Function
Phosphorus 3
inorganic
phosphates (PO4)
Constituent of
nucleic acids,
nucleotides,
phospholipids,
LPS, teichoic acids
Sulfur 1
SO4, H2S, So,
organic sulfur
compounds
Constituent of
cysteine,
methionine,
glutathione,
several
coenzymes
Potassium 1 Potassium salts
Main cellular
inorganic cation
and cofactor for
certain enzymes

11. Element % of dry weight Source Function
Magnesium 0.5 Magnesium salts
Inorganic cellular
cation, cofactor for
certain enzymatic
reactions
Calcium 0.5 Calcium salts
Inorganic cellular
cation, cofactor for
certain enzymes
and a component
of endospores
Iron 0.2 Iron salts
Component of
cytochromes and
certain nonheme
iron-proteins and a
cofactor for some
enzymatic
reactions