Question

Which of the following have the ability to convert nitrite to nitrate
(A). Nitrobacter
(B). Nitrosomonas
(C). Nitrosospira
(D). Nitrococcus
Choose the correct answer from the options given below:

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

Hint:

To remember the steps of nitrification easily: Genera starting with "Nitroso-" (e.g., Nitrosomonas) oxidize ammonia to nitrite, while genera starting with "Nitro-" (e.g., Nitrobacter, Nitrococcus) oxidize nitrite to nitrate.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Nitrification is a two-step aerobic biological process carried out by specialized chemoautotrophic soil bacteria to convert ammonia to nitrate.

Step 2: Detailed Explanation:
The nitrification process occurs in two distinct oxidation stages, carried out by different groups of bacteria:
1. Ammonia Oxidation (Ammonia to Nitrite):
Ammonia-oxidizing bacteria (AOB) oxidize ammonia (\(\text{NH}_4^+\)) to nitrite (\(\text{NH}_2^-\)).
Key genera responsible for this step include Nitrosomonas (B) and Nitrosospira (C).
2. Nitrite Oxidation (Nitrite to Nitrate):
Nitrite-oxidizing bacteria (NOB) oxidize nitrite (\(\text{NH}_2^-\)) to nitrate (\(\text{NH}_3^-\)).
Key genera responsible for this step include Nitrobacter (A) and Nitrococcus (D) (specifically Nitrococcus mobilis, a marine nitrite oxidizer).
Therefore, Nitrobacter (A) and Nitrococcus (D) are the organisms with the capacity to convert nitrite to nitrate.

Step 3: Final Answer:
The correct combination is (A) and (D) only, corresponding to option (B).