NUTRITIONAL GROUPS OF MICROORGANISMS

 NUTRITIONAL GROUPS OF MICROORGANISMS 

1. Classification of Microbial Nutrition based on Carbon sources 

a) Autotrophs 

• Autotrophs are any organisms that are capable of producing their own food. For most, this is achieved by using light energy, water and carbon dioxide (Example – Algae and Cyanobacteria). 
• All autotrophs use non-living material (inorganic sources) to make their own food. 

b) Heterotrophs 

• Heterotrophs are organisms that obtain their energy (nutrition) from Organic compounds. 

2. Classification of Microbial Nutrition based on Energy sources 

a) Phototrophs

• Phototrophs are organisms that use light as their source of energy to produce ATP and carry out various cellular processes.
• Phototrophs capture light energy and convert it into chemical energy inside their cells.
• Common examples include Green plants, Algae, Cyanobacteria, Purple non-sulphur bacteria and Heliobacteria. 

b) Chemotrophs 

• Chemotrophs obtain energy from the oxidation of chemical compounds (either organic or in organic). 
• Chemotrophs generally perform Chemosynthesis.
• Common examples include Nitrosomonas and Acidithiobacillus ferrooxidans. 

3. Classification of Microbial Nutrition based on Electron sources 

a) Lithotrophs

• Lithotroph is an organism that uses an Inorganic substrate as electron source for biosynthesis or energy conservation via aerobic or anaerobic respiration.
• The term "Lithotroph" was created from the Greek terms 'Lithos' and 'troph', meaning "Eaters of rock". 
• Lithotrophs belong to either the domain Bacteria or Archaea. Many Lithoautotrophs are Extremophiles.

b) Organotrophs

• Organotrophs are an organism that obtains hydrogen or electrons from organic substrates.
• Some Organotrophs such as many bacteria, are also Heterotrophs in nature. 
• Organotrophs can be either Anaerobic or Aerobic.

4. Four major Nutritional classes of Microorganisms based on their primary sources of Carbon, Energy and Electrons

S. No	Nutritional type	Carbon Source	Energy Source	Electron Source	Examples
1	Phtotolithotrophic autotrophs (or) Photoautotrophs (or) Photolithoautotrophs	Carbon-di-oxide	Light	Inorganic electron donors	Algae, Purple Sulfur Bacteria, Green Sulfur Bacteria and Cyanobacteria
2	Photoorganotrophic heterotrophy (or) Photoorganoheterotrophy	Organic carbon sources (CO2 may also be used)	Light	Organic electron donors	Purple Non-sulfur Bacteria and Green Non-Sulfur Bacteria
3	Chemolithotrophic autotrophs (or) Chemolithoautotrophy	Carbon-di-oxide	Inorganic chemicals	Inorganic electron donors	Sulfur-oxidizing bacteria, Hydrogen- oxidizing bacteria, Nitrifying bacteria, Methanogens and Iron-oxidizing bacteria.
4	Chemoorganotrophic heterotrophs (or) Chemoorganoheterotrophy	Organic Carbon source	Organic chemicals	Organic electron donors	Protozoa, Fungi, Archaea and Non -photosynthetic bacteria