Question

A free living anaerobic nitrogen fixer is

• A. Beijernickia
• B. Rhodospirillum
• C. Rhizobium
• D. Azotobacter

Answer 1

The correct option is B

Rhodospirillum

The correct option is : B.

Explanation of the correct option:

1. Nitrogen fixation is the mechanism in which the atmospheric nitrogen is fixed into the forms in which it can be easily absorbed by plants.
2. There are two types of nitrogen-fixing species: symbiotic species and non-symbiotic species.
3. Symbiotic species are those species of bacteria that form symbiotic relationship with other organisms like Bradyrhizobium and Rhizobium
4. Non-symbiotic species are those species which are free-living bacteria like Anabaena, Nostoc, and Cyanobacteria.
5. Rhodospirillum are the free living, anaerobic, nitrogen fixing bacteria.

Explanation of the incorrect options:

Option A:

Beijerinkia are the free living, aerobic, nitrogen fixer, which utilizes a range of multi carbon compounds.

Option C:

Rhizobium is a symbiotic nitrogen fixing bacterium, which shows symbiosis with leguminous plants and are gram negative, aerobic bacteria.

Option D:

Azotobacter is a free living aerobic, diazotrophic nitrogen fixer which requires oxygen to grow.

Final answer: A free living anaerobic bacterium capable of fixing nitrogen is Rhodospirillum.