Modes of Nutrition of Bacteria
Nutrition of Bacteria:- 2 types of bacteria based upon nutrition -
1. Autotrophic
2. Heterotrophic
1. Autotrophic:- The bacteria which synthesis their own food from the simple inorganic compound, are called autotrophic. 2 types -
a. Chemosynthertic
b. Photosynthertic
a. Chemosynthertic:- These bacteria prepare their food by using chemical energy. They get energy for food synthesis by the oxidation of certain inorganic substances such as ammonia, nitrites, nitrate, ferrous iron, hydrogen sulphides and a number of metalic or non matelic materials avialable in the environment.
i. Sulphur bacteria:- They use chemical energy while there is oxidation of sulphur compound.
Eg.- Thiobacillus
2H2S + O2 ➔ 2S + 2H2O + Energy
ii. Iron bacteria:- They use chemical energy while there is oxidation compound (Fe2+ to Fe3+).
Eg.- Leptothrix, Ferobacillus, Cladothrix
4FeCO3 + O2 + 6H2O ➔ 4Fe(OH)3 + 4CO2 + Energy
iii. Hydrogen bacteria:- They use chemical energy while there is oxidation of molecular hydrogen.
Eg.- Pseudomonas, Hydrogenomonas, Bacillus pectotrophus.
H2 + ½ O2 ➔ H2O + Energy
iv. Nitrifying bacteria:- They use chemical energy while there is oxidation of nitrogen compound.
Eg.- Nitrosomonas, Nitrobacter
2NO2 + O2 ➔ 2NO3 + Energy
b. Photosynthertic:- 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 because there is no release of oxygen in photosynthesis.
Such photosynthesis is called anoxygenic photosynthesis. It is of following types:
i. Green sulphur bacteria:- The photosynthetic pigment is chlorobium chlorophyll and sulphur is by-product. Eg.- Chlorobium
6CO2 + 12H2S + Light ➔ C6H12O6 + 12S + 6H2O
ii. Purple sulphur bacteria:- The photosynthetic pigment is bacteriochlorophyll and sulphur is by-product. Eg.- Chromatium
6CO2 + 12H2S + Light ➔ C6H12O6 + 12S + 6H2O
iii. Non-sulphur bacteria:- The photosynthetic pigment bacteriochlorophyll and sulphur is not a by-product. Eg.- Rhodopseudomonas
6CO2 + 12H2 + Light ➔ C6H12O6 + 6H2O
2. Heterotrophic:- They cannot synthesized organic compounds from the simple inorganic substances.
a. Saprophytic
b. Parasitic
c. Symbiotic
a. Saprophytic:-
> They grow in dead, decaying organic material and live by digesting and absorbing them.
> These bacteria gradually break down complex organic compounds into simpler products. For doing so they secreting the enzymes.
> The break down of carbohydrate is called fermentation (Lactic acid bacteria).
> The break down of protein material called putrefaction (Nitrifying bacteria).
b. Parasitic:-
> They live on and within other organisms (host) and they obtain their nutrition from the host.
> They live on or within the organisms both plants and animals.
> If the parasitic bacteria cause diseases and are harmful for their host they are called pathogenic. Many diseases including plant and animal including the man are caused by the pathogenic bacteria. Eg.- Vibrio cholerae, Diplococcus pneumoniae.
> If the parasitic bacteria cannot cause diseases and are harmless for their host they are called nonpathogenic.
c. Symbiotic:-
> They live in close association with other living organisms so that they both are benefited to each other, neither of them is harmed.
> Certain plants establish a symbiotic relationship with bacteria, enabling them to produce nodules that
facilitate the conversion of atmospheric nitrogen to ammonia. Eg.- Rhizobium.
> It appears that not only must the plant have a need for nitrogen fixing bacteria, but they must also be able to synthesize cytokinins which promote the production of root nodules, required for nitrogen fixation.