Explain the mode of nutrition in bacteria.

Explanation

On the basis of their mode of nutrition bacteria are classified into two types namely autotrophs and heterotrophs.
I. Autotrophic bacteria : Bacteria which can synthesis their own food are called autotrophic bacteria. They may be further subdivided as
A. Photoautotrophic bacteria - Bacteria use sunlight as their source of energy to synthesize food. They may be :
1. Photolithotrophs : In Photolithotrophs the hydrogen donor is an inorganic substance.
(a) Green sulphur bacteria : In this type of bacteria the hydrogen donor is `H_2S` and possess pigment called Bacterioviridin. Example : Chlorobium.
(b) Purple sulphur bacteria : For bacteria belong to this group the hydrogen donor is thiosulphate , Bacteriochlorophyll is present. Chlorophyll containing chlorosome are present. Example : Chromatium.
2. Photoorganotrophs : They utilize organic acid or alcohol as hydrogen donor. Example :Purple non-sulphur bacteria - Rhodospirillum.
B. Chemoautotrophic bacteria - They do not have photosynthetic pigment hence they cannot use sunlight energy. These type of bacteria obtain energy from organic or inorganic substance.
1. Chemolithotrophs : This type of bacteria oxidize inorganic compound to release energy.
Example : 1. Sulphur bacteria - Thiobacillus thiooxidans
2. Iron bactria - Ferrobacillus ferrooxidans
3. Hydrogen bacteria - Hydrogenomanas and
4. Nitrifying bacteria - Nitrosomonas and Nitrobacter.
2. Chemoorganotrophs : This type of bacteria oxidize organic compound to release energy.
Examples : 1. Methane bacteria - Methanococcus
3. Lactic acid bacteria - Lactobacillus
II. Heterotrophic bacteria : They are parasites (Clostridum and Mycobacterium), Saprophytes (Bacillus myciodes) or symbiotic (Rhizobium in root nodules of leguminous crops).