Nutrition in Bacteria

Most of the bacteria do not contain chlorophyll. They are unable to synthesise their own food, but a small group of bacteria are capable of synthesising their own food. So, nutrition in bacteria is both autotrophic and heterotrophic.

Autotrophic

These bacteria can prepare their food by using raw materials and external energy. They are of following types:

Photoautotrophic:

They can prepare their food by using solar energy in the presence of photosynthetic pigment bacteriochlorophyll and chlorobium chlorophyll. Photosynthesis in bacteria differs from other green plants photosynthesis because there is no release of oxygen in photosynthesis. Such photosynthesis is called anoxygenic photosynthesis.

C0₂ ( or another compound)₍+ H₂S ? C₆H₁₂O₆ + S ( Conditions required: Bacteriochlorophyll or chlorobium chlorophyll)

It is of following types they are:

Green sulphur bacteria

In this bacteria, the photosynthetic pigment is chlorobium chlorophyll and sulphur is by- product. Eg; Chlorobium

Purple sulphur bacteria

In this bacteria, the photosynthetic pigment is bacteriochlorophyll and sulphur are by- product. Eg; Chromatium

Non- sulphur bacteria

They have photosynthetic pigment bacteriochlorophyll and sulphur is not a by-product. Eg; Rhodopseudomonas

Chemoautotrophic

These bacteria prepare their food by using chemical energy in the absence of photosynthetic pigment. This process is called chemosynthesis. It is of following types:

Sulphur bacteria

They use chemical energy while there is oxidation of sulphur compound. Eg; Thiobacillus

2H₂S or S₂ + O₂? 2S + 2H₂O + energy

Iron bacteria

They use chemical energy while there is oxidation compound ( Fe²⁺? Fe³⁺). Eg; Leptothrix

4FeCO₃ + O₂+ 6H₂O ? 4Fe(OH)₃ + 4CO₂+ Energy

Hydrogen bacteria

They use chemical energy while there is oxidation of molecular hydrogen. Eg; Pseudomonas

H₂ + 1/20₂? H2O + Energy

Nitrifying bacteria

They use chemical energy while there is oxidation of nitrogen compound. Eg; Nitrosomonas, Nitrobacter

2NO₂ + O₂ ? 2NO₃+ Energy ( Conditions required: Nitrosomonas)

Heterotrophic

These bacteria cannot prepare their food themselves. They obtain their food or nutrition from an outside source. It is of following types:

Parasitic

Parasitic bacteria live on and within other organisms(host) and they obtain their nutrition from the host. If the parasitic bacteria cause diseases and harmful for their host they are called pathogenic. If the parasitic bacteria cannot cause diseases and harmless for their host they are called non-pathogenic. Eg;

Cholera? Vibrio Cholerae

Pneumonia? Diplococcus pneumoniae

Saprophytic

These bacteria live and grow in dead and decaying organic matters and they obtain their nutrition from dead and decaying organic matters. Firstly they secrete decomposing enzymes which convert complex organic matter into simple and soluble form. These simple and soluble organic matters are absorbed by body surface of saprophytes. Eg; Pseudomonas

Symbiotic

Symbiotic bacteria live in close association with other living organisms so that they both are benefited to each other, neither of them is harmed. Eg; Rhizobium