Explain the mode of nutrition in bacteria.

Explanation

Nutrition :
On the basis. of their mode of nutrition, bacteria are classified into two types:
1. Autotrophic Bacteria :
Bacteria which can synthesis their own food are called autotrophic bacteria. Further subdivided as:
A. Photoautotrophic bacteria :
Bacteria use sunlight as their source of energy to synthesize food. They are:
1. Photolithotrophs :
Hydrogen donor is an inorganic substance.
a. Green sulphur bacteria :
Hydrogen donor is `H_(2)S` and possess pigment called Bacterioviridin.
Eg : Chlorobium.
b. Purple sulphur bacteria
Hydrogen donor is thiosulphate, Bacteriochlorophyll is present. Chlorophyll containing chlorosomes are present. Eg: Chromatium
2. Photoorganotrophs :
They utilize organic acid or alcohol as hydrogen donor.
Eg : Purple non sulphur bacteria Rhodospirillum.
B. Chemoautotrophic bacteria :
Do not have photosynthetic pigment hence they cannot use sunlight energy. This type of bacteria obtains energy from organic or inorganic substance.
1. Chemolithotrophs :
This type oxidize inorganic compound to release energy Eg : Sulphur bacteria - Thiobacillus , thiooxidans
2. Chemo-organotrophs :
This type oxidize organic compounds to release energy.
Eg : Methane bacteria - Methanococcus
II. Heterotrophic Bacteria :
They are Parasites (Clostridium, Mycobacterium) Saprophytes (Bacillus mycoides) or Symbiotic (Rhizobium in root nodules of leguminous crops).