Question

A free living aerobic bacteria capable of fixing nitrogen is
A) Azotobacter
B) Rhizobium
C) Clostridium botulinum
D) Streptomyces

Answer 1

They are aerobic and free-living microbes present in soil, which play a significant role in the nitrogen cycle in nature, binding atmospheric nitrogen, which is inaccessible to plants, and releasing it within the sort of ammonium ions into the soil. It is usually motile, oval or spherical bacteria that form thick-walled cysts.

Complete answer:
The nitrogen inside the air is converted into ammonia or similar nitrogenous compounds in soil, this process is known as Nitrogen fixation. The Azotobacter are aerobic and free-living microbes present in soil, which play a significant role within the organic process in nature, binding atmospheric nitrogen, which is inaccessible to plants, and releasing it within the form of ammonium ions into the soil. They are usually motile, oval or spherical bacteria that form thick-walled cysts and may produce large quantities of capsular slime.

Additional Information:
-The total composition of air in the earth’s atmosphere consists of 78% nitrogen gas. Many cellular components are also made up of nitrogen. Despite all of it, the concentration of a usable form of nitrogen is very less. Nitrogen gas is vital but a limiting element. All organisms require nitrogen for their daily cellular activities.
-Nitrogen fixation is important in life because fixed inorganic nitrogen compounds are required for the biosynthesis of all nitrogen-containing organic compounds, like amino acids and proteins, nucleoside triphosphates and nucleic acids.
-As a part of the organic process, it's essential for agriculture and therefore the manufacture of fertilizer.
-It is also, indirectly, relevant to the manufacture of all nitrogen chemical compounds, which incorporates some explosives, pharmaceuticals, and dyes.
-Some organisms fix nitrogen by acting as symbiotic organisms.
-Nitrogen fixation occurs between some termites and fungi. It occurs naturally in the air by means of nitrogen-di-oxide production by lightning.
So, the correct answer is ‘Azotobacter’.

Note: The nitrogen fixation process is affected by enzymes called nitrogenases. These enzymes contain iron. Nitrogen within the atmosphere is very stable and nonreactive. Atmospheric nitrogen is molecular dinitrogen, a closely nonreactive molecule that's metabolically useless.