Introduction to the Microbial Nutrition

Microbial cells carry out several functions, which include metabolic processes and growth.
For these processes, energy sources are required, which are obtained by nutrients.
Nutrients are those substances that are energy sources to drive the metabolic or biosynthetic processes by the microbial cells.
Microbial nutrition are classified into two types based on the requirements.

The microbial cell is composed of some major elements such as Carbon, Oxygen, Hydrogen, Phosphorous, Sulfur, Potassium, iron, magnesium, and calcium. These are known as macronutrients or macroelements.
- They are needed by microbial cells in large amounts.
For biosynthesis of macromolecules such as carbohydrates, proteins, nucleic acids, etc, macroelements (C, H, O, S, and N ) are required.
Other macroelements such as K, Fe acts as a cation or participate in other several roles in microbial cells.
Microelements such as Zinc, Cobalt, Magnesium, Copper, Nickel, and Molybdenum, are needed in small amounts.
- They are also called trace elements.
- Microelements are part of cofactors & enzymes and act as catalysts in the reactions carried within the cell.
- For e.g., Zn is available at the enzyme’s active sites.

Nutrition required by the microbes

Usually, microorganisms require all three sources i.e., carbon, energy, and electron sources,
As there are a diversity of microorganisms present in our environments, their nutritional requirements also vary.

Nutritional Type	Carbon Source	Energy Source	Electron Source	E.g of Microorganisms
Photolithoautotrophy	CO₂	Light	Inorganic e^– donors	cyanobacteria, Purple & green sulfur bacteria,
Photoorganoheterotrophy	Organic carbon or maybe CO₂	Light	Organic e^– donor	Purple & Green non-sulfur bacteria
Chemolithoautotrophy	CO₂	Inorganic chemicals	Inorganic e^– donors	Iron-oxidizing bacteria, methanogens, Sulfur-oxidizing bacteria, nitrifying bacteria
Chemolithoheterotrophy (Mixotrophy)	Organic carbon or maybe CO₂	Inorganic chemicals	Inorganic e^– donors	Few sulphur-oxidizing bacteria e.g., Beggiatoa
Chemoorganoheterotrophy	Organic carbon	Organic chemicals	Organic e^– donor	Non-photosynthetic microbes

Some organic compounds are important for microbial growth but cannot be synthesized by few microbes, they are known as growth factors.
Generally, they are obtained from precursors present in the environments.
The types of growth factors are Vitamins, amino acids, purines & pyrimidines.
On the other hand, microbes that are capable of producing vitamins are exploited for commercial use. For e.g., Riboflavin is produced by Candida, Ashbya, Clostridium.