Question

A free living aerobic bacteria capable of fixing nitrogen is

• A. Azotobactor
• B. Rhizobium
• C. Clostridium botulinum
• D. Streptomyces

Answer 1

The correct option is A Azotobactor

Azotobacter is a free-living aerobic rod-shaped soil bacteria; it is a member of Gammaproteobacteria and fixes the atmospheric nitrogen into the useable form which makes option A correct. Rhizobium is a Gram-negative, motile, rod-shaped bacteria that forms special nitrogen-fixing organs, called as root nodules, in the roots of legumes and fix the gaseous nitrogen into ammonia. Option B is incorrect. Clostridium is an anaerobic free-living nitrogen fixer which makes option C incorrect. Streptomyces is filamentous free-living aerobic bacterium; S. thremoautotropicus have oxygen insensitive nitrogenase enzyme and ability to fix nitrogen. Since not all the Streptomyces spp can fix nitrogen, options D is incorrect.

Thus, the correct answer is option A.