Question

Microorganisms that oxidise ammonia to nitrite
(A). Nitrosomonas
(B). Thiobacillus
(C). Nitrobacter
(D). Nitrosolobus

Choose the correct answer from the options given below:

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

Hint:

All nitrifying bacteria whose names start with the prefix "Nitroso-" (like Nitrosomonas) convert ammonia to nitrite, while those starting with "Nitro-" (like Nitrobacter) convert nitrite to nitrate.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Biological nitrification is a two-step process carried out by distinct groups of specialized chemolithoautotrophic bacteria.

Step 2: Detailed Explanation:
The oxidation steps in nitrification are:
Ammonia Oxidation: Ammonia (\(\text{NH}_3/\text{NH}_4^+\)) is oxidized to nitrite (\(\text{NO}_2^-\)) by Ammonia-Oxidizing Bacteria (AOB).
Genera belonging to this group include Nitrosomonas (A), Nitrosolobus (D), Nitrosospira, and Nitrosococcus.
Nitrite Oxidation: Nitrite (\(\text{NO}_2^-\)) is oxidized to nitrate (\(\text{NO}_3^-\)) by Nitrite-Oxidizing Bacteria (NOB), such as Nitrobacter (C) and Nitrospira.
Thiobacillus (B) is a genus of sulfur-oxidizing bacteria and is not involved in nitrogen oxidation.
Thus, only Nitrosomonas and Nitrosolobus oxidize ammonia to nitrite.

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