Question

Nitrification is a two-step process which refers to the conversion of ammonium (\(\text{NH}_4^+\)) to nitrate (\(\text{NO}_3^-\)).
(A). Nitrification is a two-step process which refers to the conversion of ammonium (\(\text{NH}_4^+\)) to nitrate (\(\text{NO}_3^-\)).
(B). In the first step, Nitrosomonas (obligate autotrophic bacteria) convert ammonium (\(\text{NH}_4^+\)) to nitrite (\(\text{NO}_2^-\)).
(C). The second step of nitrification occurs through Nitrobacter and Nitrosolobus species, which convert nitrite (\(\text{NO}_2^-\)) to nitrate (\(\text{NO}_3^-\)).
(D). The second step of nitrification occurs through Nitrobacter species only, which convert nitrite (\(\text{NO}_2^-\)) to nitrate (\(\text{NO}_3^-\)).
Choose the correct answer from the options given below:

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

Hint:

To remember the biological actors in nitrification:
-
Step 1: Nitroso- genus (Nitrosomonas, Nitrosolobus, Nitrosococcus) oxidizes \(\text{NH}_4^+\) to \(\text{NO}_2^-\).
-
Step 2: Nitro- genus (Nitrobacter, Nitrospira) oxidizes \(\text{NO}_2^-\) to \(\text{NO}_3^-\).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Nitrification is the biological oxidation of ammonium to nitrate, mediated by distinct groups of chemolithoautotrophic bacteria.

Step 2: Detailed Explanation:
- Statement A is correct: Nitrification is a two-step biological oxidation process converting \(\text{NH}_4^+\) to \(\text{NO}_3^-\).
- Statement B is correct: In the first step, ammonia-oxidizing bacteria (AOB), primarily Nitrosomonas, oxidize ammonium to nitrite: \[ 2\text{NH}_4^+ + 3\text{O}_2 \rightarrow 2\text{NO}_2^- + 4\text{H}^+ + 2\text{H}_2\text{O} \] - Statement C is incorrect: Nitrosolobus is an ammonia-oxidizer (Step 1), not a nitrite-oxidizer (Step 2).
- Statement D is correct: The second step (nitrite oxidation) is carried out by nitrite-oxidizing bacteria (NOB), primarily Nitrobacter species, which convert nitrite to nitrate: \[ 2\text{NO}_2^- + \text{O}_2 \rightarrow 2\text{NO}_3^- \] - Therefore, statements (A), (B), and (D) are correct.

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