Consider the following bacteria:
1. Rhizobium
2. Azotobacter
3. Anabaena
4. Nostoc
Which among the above fix nitrogen without being in symbiotic relation with other biota?

Answer: [B] Only 2, 3 & 4

Two kinds of nitrogen-fixing bacteria are recognized:

  • Free-living (non-symbiotic) bacteria, including the cyanobacteria (or blue-green algae) Anabaena and Nostoc and genera such as Azotobacter, Beijerinckia, and Clostridium;
  • Mutualistic (symbiotic) bacteria such as Rhizobium, associated with leguminous plants (e.g., various members of the pea family), and certain Azospirillum species, associated with cereal grasses.

This question is a part of GKToday's Integrated IAS General Studies Module