Nitrogen Cycle:
Nitrogen Cycle is a biogeochemical process through which nitrogen converted into many forms. It consecutively passes from the atmosphere to the soil to the organism and back into the atmosphere. It involves several processes such as nitrogen fixation, nitrification, denitrification, decay, and putrefaction.
1. Chemosynthetic Bacteria: They oxide inorganic substances and utilize the obtained energy converting the carbon dioxide into organic material. On the basis of different inorganic substances oxidized by them, the following forms are recognized:
i. Nitrifying Bacteria: They occur freely in soil and are of two types. Nitrosomonas oxidize the ammonium salts into nitrites and Nitrobacter oxidize nitrites into nitrites. They are anaerobic and utilize free oxygen for oxidation.
ii. Denitrifying Bacteria: They are found in oxygen-deficient soils as main places. They convert nitrates into nitrites and free nitrogen is liberated. They are anaerobic bacteria such as Pseudomonas aeruginosa, and Micrococcus denitrificans.
iii. Sulphur Bacteria: They oxidize sulphurated hydrogen to water and free sulfur. This free sulfur is deposited as granules in the cytoplasm. They are aerobic such as Thiobacillus.
iv. Iron Bacteria: These oxidize ferrous carbonate to ferric carbonate and the liberated energy is utilized. They are aerobic such as Ferrabacillus.
v. Hydrogen Bacteria: These oxidize hydrogen to water with the help of some oxides of nitrogen. They are aerobic such as Hydrogenomonas.
vi. Carbon Bacteria: They oxidize charcoal and damp coal into CO2 in presence of free oxygen. They are aerobic such as Carboxydomonus.
vii. Methane Bacteria: These oxidise methane CH3 to CO2 and HO2. They are aerobic such as Methanomonas.
2. Photosynthetic Bacteria: Very few bacteria contain a red pigment which helps in the synthesis of carbohydrates in presence of sunlight and is therefore known as photosynthetic bacteria. Recently in some bacteria bacteriochlorophyll has been observed. It appears to be evenly distributed throughout the cytoplasm. With the aid of the electron microscope, the pigment appears to be in minute grana somewhat different from those of the chloroplasts in the higher plants. These bacteria may well be considered independent.