- Micro elements
Micro elements are required in very small amounts by microbial cells and are also called trace elements. They are normally a part of enzymes and cofactors and they aid in the catalysis of reactions.
It is present at the active sites of some enzymes.
It aids many enzymes in catalysing the transfer of phosphate group.
It is required for nitrogen fixation.
It is a component of vitamin B12 and related co-enzymes.
Trace elements are often present as contamination of tap water and other components of culture media in amounts sufficient to support microbial growth.
In addition to the requirement of common macro elements and trace elements, some microbial groups may even have some specific mineral requirements. For example, diatoms and certain other algae synthesise cell walls with silica. Therefore diatoms have a specific requirement of silicic acid H4SiO4 to construct their cells walls. Bacteria growing in saline lakes and oceans require large amount of sodium.Most microorganisms can synthesis all the building blocks form the macro and micro elements but if they cannot it must be supplied in environment or the medium. Such essential building blocks are called growth factors.
The three types of growth factors most often required in microbial nutrition are :
- Amino acids
These are required in the medium for growth of such microbes, which cannot synthesize more than one or few of the 21 amino acids that are required for protein synthesis. For example lactic acid bacteria require the whole complement, whereas most strains of Staphylococcus epidermidis, a normal inhabitant of human skin requires six amino acids ( proline, valine, arginine, tryptophan, histidine and leucine)
2. Purines and pyrimidines
These are required for nucleic acid synthesis. The need for adding nucleic acid bases to the growth medium is rare for free living soil microorganisms, but is most often observed in lactic acid bacteria and othe fastidious organisns with many growth factor requirements.
These are small organic molecules that function either as co-enzymes for several enzymes or as the building blocks for co-enzymes. Very small amounts of vitamins are required to sustain the growth of microorganisms. The vitamins most frequently required by microorganisms are those that are less susceptible to destruction by light, for example thiamine, biotin and nicotinic acid.
*Turgor Pressure – The water pressure inside plant cells is called turgor pressure, and is maintained by a process called osmosis.