Question

Which of the soil bacteria convert ammonium into nitrite?

• A. Nitrogen-fixing bacteria
• B. Nitrifying bacteria
• C. Denitrifying bacteria
• D. Ammonifying bacteria

Hint:

Nitrifying = Ammonium $\rightarrow$ Nitrite $\rightarrow$ Nitrate. Think of it as the "Cleaning" process of the nitrogen cycle.

Answer 1

The Correct Option is B

Concept: The nitrogen cycle involves several distinct groups of bacteria that transform nitrogen through various oxidation and reduction states.

Step 1: Defining Nitrification.
The process of converting ammonium ($NH_{4}^{+}$) into nitrate (${NO_{3}}^{-}$) is called nitrification. This is a two-step aerobic process carried out by specialized chemoautotrophic bacteria known collectively as nitrifying bacteria.

Step 2: Identifying the specific step.
The first step of nitrification is the oxidation of ammonium to nitrite ($NO_{2}^{-}$). This is primarily performed by bacteria such as Nitrosomonas. The second step (nitrite to nitrate) is performed by Nitrobacter.

Step 3: Eliminating Others.
Nitrogen-fixing bacteria (1) convert $N_2$ to $NH_3$. Denitrifying bacteria (3) convert nitrate back into gaseous $N_2$. Ammonifying bacteria (4) break down organic matter into ammonium.