Nutrition I Classification of Bacteria Based on Nutrition

Classification of Bacteria Based on Mode of Nutrition:

Bacteria can be classified based on their mode of nutrition, which refers to how they obtain energy and nutrients for survival and growth. The two main categories of bacteria based on nutrition are Autotrophic and Heterotrophic bacteria.

 

[1] Autotrophic Bacteria (Self-Feeding Bacteria):

• These bacteria can synthesize their own food using inorganic substances.
• They obtain carbon from carbon dioxide (CO₂) and energy from either light or chemical reactions.
• They are further divided into two types:

(A) Photosynthetic Autotrophs (Phototrophic Bacteria)

• These bacteria use sunlight as an energy source to produce organic compounds through photosynthesis.
• Instead of chlorophyll, they contain bacterial chlorophyll or bacteriochlorophyll.
• They can be divided into two types:

1. Oxygenic Photosynthetic Bacteria:

   • Use water (H₂O) as an electron donor and release oxygen (O₂) during photosynthesis.
   • Example: Cyanobacteria (Anabaena, Nostoc).

2. Anoxygenic Photosynthetic Bacteria:

   • Do not produce oxygen because they use hydrogen sulfide (H₂S) or other substances instead of water.
   • Example: Purple sulfur bacteria (Chromatium), Green sulfur bacteria (Chlorobium).

(B) Chemosynthetic Autotrophs (Chemotrophic Bacteria)

• These bacteria obtain energy by oxidizing inorganic substances such as ammonia, nitrites, sulfur, or iron.
• They play a significant role in nutrient cycling (e.g., nitrogen fixation, sulfur oxidation).
• Examples:
  • Nitrifying bacteria: Convert ammonia into nitrates (e.g., Nitrosomonas, Nitrobacter).
  • Sulfur bacteria: Oxidize hydrogen sulfide to sulfur (e.g., Thiobacillus).
  • Iron bacteria: Oxidize iron compounds (e.g., Ferrobacillus).

 

[2] Heterotrophic Bacteria (Dependent on Organic Matter):

• These bacteria cannot synthesize their own food and depend on organic compounds for carbon and energy.
• They obtain nutrition from living or dead organisms.
• They are further classified into:

(A) Saprophytic Bacteria (Decomposers)

• These bacteria obtain nutrients from dead and decaying organic matter.
• They play a vital role in decomposition and nutrient recycling.
• Example: Bacillus subtilis, Pseudomonas fluorescens.

(B) Parasitic Bacteria (Disease-Causing Bacteria)

• These bacteria depend on a living host for nutrition and often cause diseases.
• They can be obligate parasites (completely dependent on a host) or facultative parasites (can survive outside a host).
• Examples:
  • Mycobacterium tuberculosis (causes tuberculosis)
  • Salmonella typhi (causes typhoid fever)

(C) Symbiotic Bacteria (Mutually Beneficial Relationship)

• These bacteria live in association with other organisms, and both benefit from the relationship.
• Examples:
  • Rhizobium (fixes nitrogen in root nodules of leguminous plants).
  • Escherichia coli (lives in the human intestine and helps in digestion).

(D) Facultative Bacteria (Adaptable Bacteria)

• These bacteria can switch between autotrophic and heterotrophic modes depending on environmental conditions.
• Example: Euglena (acts as an autotroph in light and heterotroph in the absence of light).