In nitrification, ammonia is first oxidised to nitrite by

Options

A. (a) Nitrosomonas and Nitrococcus
B. (b) Nitrosomonas and Nitrobactor
C. (c) Pseudomonas and Nitrococcus
D. (d) Pseudomonas and Thiobacillus

Answer

### Step-by-Step Solution:

1. **Understanding Nitrification**:
- Nitrification is a two-step process in the nitrogen cycle where ammonia is converted into nitrite and then into nitrate. This process is crucial for making nitrogen available to plants.

2. **First Step of Nitrification**:
- The first step involves the oxidation of ammonia (NH₃) to nitrite (NO₂⁻).

3. **Role of Enzymes**:
- This oxidation process is facilitated by specific enzymes. The first enzyme involved is called **ammonia monooxygenase**, which converts ammonia into hydroxylamine.

4. **Conversion to Nitric Oxide**:
- Hydroxylamine is then converted into nitric oxide (NO) through the action of another enzyme known as **oxidoreductase**.

5. **Formation of Nitrite**:
- Finally, nitric oxide is further oxidized to nitrite (NO₂⁻) by the same class of enzymes, oxidoreductase.

6. **Bacteria Involved**:
- The entire process is carried out by specific types of bacteria known as **ammonia-oxidizing bacteria**. These bacteria are essential for the nitrification process.

7. **Examples of Bacteria**:
- Notable examples of ammonia-oxidizing bacteria include **Nitrosomonas** and **Nitrococcus**. These bacteria play a crucial role in the conversion of ammonia to nitrite.

8. **Conclusion**:
- Therefore, in nitrification, ammonia is first oxidized to nitrite by ammonia-oxidizing bacteria, specifically by the actions of enzymes like ammonia monooxygenase and oxidoreductase.

### Final Answer:
In nitrification, ammonia is first oxidized to nitrite by **ammonia-oxidizing bacteria** such as **Nitrosomonas** and **Nitrococcus**.

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