Biomedical Engineering Reference
In-Depth Information
TABLE 2.9
The Eight Macronutrient Elements and Some Physiological Functions and Growth Requirements
Required concentration,
mol/L
Element
Physiological function
10
2
Carbon
Constituent of organic cellular material. Often the energy source.
>
10
3
Nitrogen
Constituent of proteins, nucleic acids, and coenzymes.
Hydrogen
Organic cellular material and water.
Oxygen
Organic cellular material and water. Required for aerobic respiration.
10
4
Sulfur
Constituent of proteins and certain coenzymes.
10
4
e
10
3
Phosphorus
Constituent of nucleic acids, phospholipids, nucleotides, and certain
coenzymes.
10
4
e
10
3
Potassium
Principal inorganic cation in the cell and cofactor for some enzymes.
10
4
e
10
3
Magnesium
Cofactor for many enzymes and chlorophylls (photosynthetic
microbes) and present in cell walls and membranes.
Source: G. M. Dunn in Comprehensive Biotechnology, M. Moo-Young, ed., Vol. 1, Elsevier Science, 1985.
fermentation process, such as penicillin. Manganese (Mn) is also an enzyme cofactor and
plays a role in the regulation of secondary metabolism and the excretion of primary
metabolites.
(2)
Trace elements needed under specific growth conditions are Cu, Co, Mo, Ca, Na, Cl, Ni,
and Se. Copper (Cu) is present in certain respiratory-chain components and enzymes.
Copper deficiency stimulates penicillin and citric acid production. Cobalt (Co) is
present in corrinoid compounds such as vitamin Bu. Propionic bacteria and certain
methanogens require cobalt. Molybdenum (Mo) is a cofactor of nitrate reductase and
nitrogenase and is required for growth on NO
3
and N
2
as the sole source of nitrogen.
Calcium (Ca) is a cofactor for amylases and some proteases and is also present in some
bacterial spores and in the cell walls of some cells, such as plant cells.
Sodium (Na) is needed in trace amounts by some bacteria, especially by methanogens
for ion balance. Sodium is important in the transport of charged species in eukaryotic
cells. Chloride (Cl
) is needed by some halobacteria and marine microbes, which
require Na
þ
, too. Nickel (Ni) is required by some methanogens as a cofactor and
Selenium (Se) is required in formate metabolism of some organisms.
(3)
Trace elements that are rarely required are B, Al, Si, Cr, V, Sn, Be, F, Ti, Ga, Ge, Br, Zr, W, Li,
and I. These elements are required in concentrations of less than 10
6
mol/L and are toxic
at high concentrations, such as 10
4
mol/L.
Some ions such as Mg
2
þ
,Fe
3
þ
,andPO
3
may precipitate in nutrient medium and become
unavailable to the cells. Chelating agents are used to form soluble compounds with the precipi-
tating ions. Chelating agents have certain groups termed ligands that bind to metal ions to form
soluble complexes. Major ligands are carboxyl (
e
COOH), amine (
e
NH
2
), and mercapto (
e
SH)
groups. Citric acid, EDTA (ethylene diamine tetra-acetic acid), polyphosphates, histidine, tyro-
sine, and cysteine are themost commonly used chelating agents. Na
2
EDTA is themost common
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