Question

Which of the following is a symbiotic nitrogen-fixing bacterium?
1. Rhizobium
2. Azotobacter
3. Xanthomonas
4. Azospirillum

Answer 1

Correct Answer - Option 1 : Rhizobium

The Correct Answer is Rhizobium.

• Rhizobium is the bacteria that live in symbiotic association with the root nodules of the leguminous plants. 
  • Fixation of nitrogen cannot be done independently. 
  • That is why rhizobium requires a plant host. 
  • It is a vital source of nitrogen to agricultural soils including those in arid regions.

• Azotobacter
  • It is a genus of usually motile, oval, or spherical bacteria that form thick-walled cysts and may produce large quantities of capsular slime.
• Xanthomonas
  • It is bacterial species that cause a variety of plant diseases, including 'black rot' in cruciferous vegetables and bacterial wilt of turfgrass.
• Azospirillum
  • It is a Gram-negative, microaerophilic, non-fermentative and nitrogen-fixing bacterial genus from the family of Rhodospirillaceae.