Question

One of the free-living anaerobic nitrogen -fixing bacteria is
(a)Azotobacter
(b) Beijernickia
(c)Rhodospirillum
(d)Rhizobium

Answer 1

Hint: Nitrogen-fixing bacteria ,microorganisms have the ability to transform nitrogen into fixed nitrogen.More than 90 percent of nitrogen fixation is affected by these organisms which play a significant role in the nitrogen cycle.

Complete answer:
Let’s discuss the options and find out the correct answer
-Azotobacter-A genus of free-living diazotrophic bacteria whose resting stage is a cyst. Primarily it is found in neutral to alkaline soils in aquatic environments as well on some plants. It also has several metabolic capabilities such as atmospheric nitrogen fixation by conversion to ammonia. Azotobacter is a free-living, diazotrophic nitrogen fixer which requires oxygen to grow
This option is incorrect.
-Beijerinckia- Beijerinckia is an aerobic nitrogen fixer and they also utilize a range of multi-carbon compounds. It is a free-living nitrogen-fixing aerobic microbe and its abundant nitrogenase enzyme capable of nitrogen reduction. This option is incorrect.
-Rhodospirillum-It is a free-living, anaerobic nitrogen fixer bacteria also it can synthesize its food in presence of light under anaerobic conditions. It is a gram-negative purple nonsulfur bacteria generally its color is pink. It is the facultative anaerobe. By transforming atmospheric nitrogen into ammonia by virtue of nitrogenase enzyme in the soil a free-living bacteria helps in nitrogen fixation.
This option is correct.
-Rhizobium-It is considered as diazotroph which is capable of forming a symbiotic association with roots of legume plants which are gram-negative aerobic bacteria. This is an incorrect option
Hence the correct answer is option C.

Note: As proteins and nucleic acids are considered to be essential for supporting life on earth, therefore nitrogen fixing bacteria is also assumed to be important.Role of Nitrogen-fixing bacteria in nitrogen cycle is that convert nitrogen gas in the atmosphere to ammonia with the help of nitrogen-fixing bacteria in the soil and within the root nodules of some plants. Ammonia to nitrites or nitrates is converted by Nitrifying Bacteria .Plants absorb ammonia, nitrites, and nitrates and these are all fixed nitrogen.