Question

The organisms involved in the process of conversion of nitrate to nitrogen gas is

• A. Nitrobacter
• B. Azotobacter
• C. Thiobacillus
• D. Nitrocystis

Hint:

Nitrate to Nitrogen = Denitrification (Loss of N).
Organisms: Pseudomonas, Bacillus, and Thiobacillus.
This process occurs when the soil is "Drowning" (too much water, no air).

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The conversion of nitrate ($NO_3^-$) to nitrogen gas ($N_2$) is the process of denitrification. The question asks to identify the bacterium responsible for this reaction.
Detailed Explanation:

• Process of Denitrification:
This is an anaerobic process occurring in waterlogged or oxygen-depleted soils.
Facultative anaerobic bacteria use nitrate instead of oxygen as an electron acceptor during respiration.
The sequence is: $NO_3^- \rightarrow NO_2^- \rightarrow NO \rightarrow N_2O \rightarrow N_2$.

• Identifying the Bacteria:
{Thiobacillus denitrificans is a well-known denitrifier. It is an autotrophic bacterium that can reduce nitrates to nitrogen gas while oxidizing sulfur compounds.
Other common denitrifiers include species of Pseudomonas and Bacillus.

• Analyzing Other Options:
Nitrobacter: Involved in nitrification (converts nitrite to nitrate).
Azotobacter: Involved in nitrogen fixation (converts atmospheric $N_2$ to ammonia).
Nitrocystis: Also a nitrifying bacterium.

Step 2: Final Answer:
Among the given choices, Thiobacillus is the organism capable of carrying out denitrification.