Based on nutrition bacteria are classified into following types.
(1) Autotrophic bacteria : They synthesize their own food. They are further classified into two types ;
(A) Photoautotrophic bacteria :
They are autotrophs and synthesize their food by absorbing light energy. They contain bacteriochlorophyll and bacteriocidin to absorb light energy.
Example: Green sulphur bacteria like chlorobium, purple sulphur bacteria like chromatium. These bacteria use H2S as their source of hydrogen, so O2 is not liberated.
(B) Chemoautotrophic bacteria:
They are autotrophs, utilizes (utilises) chemical energy for the food synthesis. They get chemical energy by the oxidation of chemical substances of nature. Example: Nitrifying bacteria, sulphur bacteria etc.
(2) Hetero trophic bacteria: They do not synthesize their own food but obtain food by two methods.
- Saprophytic method.
- Parasitic method.
The bacteria obtain their food by feeding on dead organic matter are called saprophytic bacteria. The bacteria obtain their food by living inside or outside the body of other organisms are called parasitic bacteria.
