On the basis of mode of nutrition bacteria are of two types:
I. Autotrophic bacteria
II. Heterotrophic bacteria.
I. Autotrophic bacteria: They produce their own food.
They are of following types:

1. Photosynthetic bacteria: They contain different types of pigments which produce food by the utilisation of light energy e.g., Chlorobium.
2. Chemosynthetic bacteria: They produce food through various chemical reactions e.g., Bagiatoa.

II. Heterotrophic bacteria: They are of following types:

1. Parasitic bacteria: They obtain their food from other organisms and are called parasites, e.g., Mycobacterium.
2. Saprophytic bacteria: They obtain their food from dead and decayed organic substances, e.g., Bacillus mycoidies.
3. Symbiotic bacteria: They form symbiotic association with higher plants, e.g., Rhizobium.