Bacteria exhibit the most extensive metabolic diversity among living organisms. While the majority of bacteria are heterotrophic (relying on other organisms or dead organic matter for food), many are autotrophic, capable of synthesizing their own food. Autotrophic bacteria are further classified into:

Photoautotrophic: Use sunlight as an energy source (e.g., Cyanobacteria).

Chemoautotrophic: Use chemical energy from the oxidation of inorganic substances (e.g., nitrifying bacteria).

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