Question

Which of the following is a free-living aerobic non-photosynthetic nitrogen-fixer?
A. Rhizobium
B. Azotobacter
C. Azospirillum
D. Nostoc

Answer 1

Hint: Atmospheric nitrogen fixation is achieved by a diverse community of prokaryotic organisms. In existence, the majority of nitrogen is extracted from the environment by microbes to form ammonia, nitrites, and nitrates which can be used by plants. Nitrogen-fixing bacteria are microorganisms capable of converting nitrogen from the atmosphere into usable forms of nitrogen compounds by plants.

Complete step by step answer: Plants can easily convert ammonia into other nitrogen compounds. This includes aquatic species such as Cyanobacteria; free-living soil bacteria such as Azotobacter; bacteria that develop associative relationships with plants such as Azospirillum, and notably, bacteria, such as Rhizobium and Bradyrhizobium, which establishes symbiosis with legumes as well as other plants. Azotobacter species are gram-negative, free-living, oxidative soil habitats, oval or spherical bacteria which form thick-walled nodules. They are aerobic in nature. There are about six varieties in the Azotobacter genus, many of which are motile by way of flagella, most of which are not. These are usually polymorphic and vary in size from 2-10 μm in length and 1-2 μm in width. Such bacteria employ atmospheric nitrogen for their cell protein synthesis. The whole-cell protein would then be oxidized in the soil just after the death of the Azotobacter cells and contributes to the nitrogen availability for the agricultural crops.
So, the correct answer is option B.

Additional information: Azotobacter has favourable impacts on crop yield, the biosynthetic pathway of biologically active compounds, enhancement of rhizospheric bacteria, the formation of phytopathogenic blockers. Azotobacter species are non-symbiotic aerobic microorganisms that are responsible for fixing an average of 20 kg N/ha/per year.

Note: Nitrogen is a vital determining factor for plant growth and development. It is a component of chlorophyll, most needed pigment required for photosynthesis, and amino acids, which have been key protein foundations. Azotobacter has developed a lot of interest throughout the research world due to its interesting method of metabolism by which they might aerobically fix nitrogen.