Nutritional Types of Microorganisms
Microorganisms can be classified into nutritional classes based on how they satisfy the requirements of carbon, energy and electrons for their growth and nutrition.
Based on the carbon source, microorganisms are able to utilize, they are classified into Autotrophs and Heterotrophs.
Autotrophs: These are organisms that utilize CO2 as their sole source of carbon.
Heterotrophs: These are organisms that use preformed organic substances from other organisms as their carbon source.
Based on energy source, microorganisms are classified into Phototrophs and Chemotrophs.
Phototrophs: These are organisms that utilize light (radiant energy) as their energy source.
Chemotrophs: These are organisms that obtain energy by oxidation of organic or inorganic compounds.
Microorganisms are classified into Lithotrophs and Organotrophs based on the source from which they extract electrons. Lithotrophs are organisms that use reduced inorganic substances as their electron source whereas Organotrophs obtain electrons from organic compounds (Table 6.1).
All microorganisms fall into any one of the four nutritional classes based on their primary source of carbon, energy and electrons.
1. Photoautotrophs: Eukaryotic algae, Cyanobacteria (Blue Green Algae) (Figure 6.1) and Purple and Green Sulphur bacteria belong to this class. They are capable of using light energy and have carbondioxide as the sole source of carbon.
2. Photoheterotrophs: These organisms make use of light as energy source and organic compounds as electron and carbon source. Example: Purple and Green Non sulphur bacteria
3. Chemoautotrophs: These are ecologically important microorganisms. They oxidize inorganic compounds like nitrate, iron and sulphur to obtain energy and electrons.
4. Chemoheterotrophs: These organisms use organic compounds to satisfy their needs of energy, electron and carbon. (Table 6.2)
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