Nitrogen Fixing Bacteria

Nitrogen Fixers (Diazotrophs):- Among the earth’s organisms, only some prokaryotes like bacteria and cyanobacteria can fix atmosphere nitrogen. They are called nitrogen fixers or diazotrophs. They fix about 95% of the total global nitrogen fixed annually by natural process.

a. Asymbionts (Free living)

b. Symbionts

a. Asymbionts (Free living):-

Bacteria:- They add up to 10-25 kg, of nitrogen/ha/annum.

> Azotobacter (Aerobic, Saprophytic)

> Beijerinckia (Aerobic, Saprophytic)

> Clostridium (Anaerobic, Saprophytic)

> Desulphovibrio (Chemotrophic)

> Rhodopseudomonas (Photoautotrophic)

> Rhodospirillum (Photoautotrophic)

> Chromatium (Photoautotrophic)

b. Symbionts:- Live in close symbiotic association with other plants.

Bacteria:- 

> Rhizobium:- It is aerobic, gram negative nitrogen fixing bacterial symbionts of legume roots. Sesbania rostrata has Rhizobium in root nodules and Aerorhizobium in stem nodules. 

> Frankia:- It is symbiont in root nodules of many non-leguminous plants like Casuarina and Alnus.

> Xanthomonas and Mycobacterium:- They occur as symbiont in the leaves of some members of the families Rubiaceae and Myrsinaceae (e.g., Ardisia).