Question

Which of the following have the ability to convert ammonia into nitrite ?
(A) Nitrosomonas
(B) Nitrosospira
(C) Nitrosococcus
(D) Nitrobacter
(E) Nitrococcus
Choose the correct answer from the options given below :

• A. (A), (B), (D) and (E) only.
• B. (A), (B), (C) and (D) only.
• C. (A), (B) and (C) only.
• D. (D) and (E) only.

Hint:

To easily differentiate these bacteria in exams: genera starting with 'Nitroso-' oxidize ammonia to nitrite, while those starting with 'Nitro-' oxidize nitrite to nitrate.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Nitrification is a key two-step biological process in the nitrogen cycle where soil bacteria oxidize ammonia into nitrate.
Each step is carried out by different, highly specialized groups of chemolithoautotrophic bacteria.

Step 2: Detailed Explanation:
Let us analyze the two steps of nitrification and the bacteria involved:
1.
Step 1: Ammonia Oxidation:
In this step, ammonia ($\text{NH}_3$) or ammonium ($\text{NH}_4^+$) is oxidized to nitrite ($\text{NO}_2^-$).
This reaction is carried out by Ammonia-Oxidizing Bacteria (AOB), which typically contain the prefix "Nitroso-" in their genus names.
These include Nitrosomonas (A), Nitrosospira (B), and Nitrosococcus (C).
2. Nitrite Oxidation:
In this step, the produced nitrite ($\text{NO}_2^-$) is further oxidized to nitrate ($\text{NO}_3^-$).
This reaction is carried out by Nitrite-Oxidizing Bacteria (NOB), which typically contain the prefix "Nitro-" in their genus names.
These include Nitrobacter (D) and Nitrococcus (E).
Therefore, only Nitrosomonas, Nitrosospira, and Nitrosococcus have the ability to convert ammonia into nitrite.

Step 3: Final Answer:
The bacteria that convert ammonia to nitrite are (A), (B), and (C) only, corresponding to option (C).