Which of the following pair represents free living nitrogen fixing aerobic bacteria?
- Pseudomonas and Thiobacillus
- Rhizobium and Frankia
- Azotobacter and Beijernickia
- Anabaena and Rhodospirillum
Answer
(3) Azotobacter and Beijernickia
Solution
As per NCERT, examples of free-living nitrogen-fixing aerobic microbes are Azotobacter and Beijernickia, while Rhodospirillum is anaerobic and free-living.
Rhizobium and Frankia, on the other hand, are symbiotic nitrogen fixers, and Pseudomonas and Thiobacillus are denitrifying bacteria.
Anabaena is a cyanobacterium and Rhodospirillum is anaerobic, so that pair does not fit either.
Answer: (3)