Nutritional Types of Microorganisms

Nutritional Types of Microorganisms:

Microorganisms exhibit diverse metabolic strategies to obtain energy and carbon for growth. Based on their source of energy, carbon, and electron donors, microorganisms are classified into different nutritional types. Understanding these nutritional categories is essential for microbiology, biotechnology, and ecology.

 

Classification of Microorganisms Based on Nutrition

Microorganisms are classified based on three main factors:

1. Energy Source – The source of energy required for metabolism.
2. Carbon Source – The source of carbon used for growth and biosynthesis.
3. Electron Source – The source of electrons for cellular reactions.

These criteria give rise to major nutritional types of microorganisms, which are summarized in the table below:

 

[1] Photoautotrophs (Photolithoautotrophs)

Energy Source: Light

Carbon Source: CO₂ (Inorganic)

Electron Source: Inorganic compounds (H₂O, H₂S)

Examples:

• • Cyanobacteria (e.g., Anabaena, Nostoc) – Oxygenic photosynthesis using water as an electron donor.
  • Purple sulfur bacteria and Green sulfur bacteria – Use H₂S instead of H₂O in photosynthesis (Anoxygenic photosynthesis).

Significance

• Primary producers in aquatic ecosystems.
• Play a crucial role in the global carbon and oxygen cycle.

 

[2] Photoheterotrophs (Photoorganoheterotrophs)

Energy Source: Light

Carbon Source: Organic compounds (e.g., fatty acids, alcohols)

Electron Source: Organic or inorganic compounds

Examples:

• • Purple non-sulfur bacteria (e.g., Rhodospirillum)
  • Green non-sulfur bacteria (e.g., Chloroflexus)

Significance

• Found in anaerobic aquatic environments.
• Use light for energy but require organic molecules as a carbon source.

 

[3] Chemoautotrophs (Chemolithoautotrophs)

Energy Source: Chemical compounds (oxidation of inorganic molecules)

Carbon Source: CO₂ (Inorganic)

Electron Source: Inorganic compounds (NH₃, NO₂⁻, H₂S, Fe²⁺, H₂)

Examples:

• • Nitrifying bacteria (e.g., Nitrosomonas, Nitrobacter) – Convert ammonia to nitrate.
  • Sulfur bacteria (e.g., Thiobacillus) – Oxidize sulfur compounds.
  • Iron bacteria (e.g., Gallionella) – Oxidize Fe²⁺ to Fe³⁺.

Significance

• Important in biogeochemical cycles (nitrogen, sulfur, iron cycles).
• Support deep-sea hydrothermal vent ecosystems.

 

[4] Chemoheterotrophs (Chemoorganoheterotrophs)

Energy Source: Chemical compounds (oxidation of organic molecules)

Carbon Source: Organic compounds (glucose, amino acids, lipids)

Electron Source: Organic compounds

Examples:

• • Bacteria: E. coli, Bacillus, Pseudomonas, Staphylococcus, Streptococcus
  • Fungi: Yeasts, Molds (Aspergillus, Penicillium)
  • Protozoa & Animals

Significance

• Pathogenic and non-pathogenic microbes belong to this group.
• Major decomposers in nature (degrade organic matter).
• Used in biotechnology for fermentation (e.g., yeast for alcohol production).

 

Special Nutritional Categories

(1) Facultative Organisms

• Can switch between different nutritional modes depending on environmental conditions.
• Example: E. coli can grow as a chemoheterotroph under aerobic conditions but can also ferment sugars anaerobically.

(2) Obligate Organisms

• Strictly depend on a specific nutritional mode.
• Example: Nitrosomonas is an obligate chemolithoautotroph (cannot survive on organic compounds).