Question

Choose the correct answer from the alternatives given.
Which of the following is free-living bacteria responsible for nitrogen fixation?

• A. Pseudomonas
• B. Rhodospirillum
• C. Azotobacter
• D. All of these

Answer 1

The correct option is D All of these

Non-symbiotic bacteria in the soil and symbiotic bacteria that live in the roots of plants are capable of nitrogen fixation. Bacteria in the genera Clostridium and Azotobacter are non-symbiotic nitrogen-fixing bacteria, while those in the genus Rhizobium are symbiotic bacteria. Pseudomonas species fixes nitrogen under microaerobic conditions in the free-living state and colonizes rice endophytically. Nitrogen fixation in phototrophic bacteria has been found in Rhodospirillum rubrum.

So, the correct option is, 'All of these'.