Which of the following bacteria is involved in the two-step conversion of `NH_(3)` into nitrate?

Options

A. Azotobacter and Nitrosomonas
B. Nitrosomonas and Nitrobacter
C. Azotobacter and Achromobacter
D. Pseudomonas and Nitrobacter

Answer

To solve the question regarding which bacteria are involved in the two-step conversion of ammonia (NH3) into nitrate (NO3-), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Process of Nitrification**:
- Nitrification is the biological process that converts ammonia into nitrate. It occurs in two main steps.

2. **Identify the First Step**:
- In the first step, ammonia (NH3 or NH4+) is oxidized to nitrite (NO2-). This step is carried out by a group of bacteria known as ammonia oxidizers.

3. **Identify the Key Bacteria for the First Step**:
- The primary bacteria responsible for this conversion from ammonia to nitrite is **Nitrosomonas**. Other bacteria like Nitrosococcus and Nitrosolobus also contribute but to a lesser extent.

4. **Identify the Second Step**:
- In the second step, nitrite (NO2-) is oxidized to nitrate (NO3-). This step is performed by nitrite-oxidizing bacteria.

5. **Identify the Key Bacteria for the Second Step**:
- The main bacteria responsible for converting nitrite to nitrate is **Nitrobacter**. Other bacteria like Nitrosospira and Nitrosococcus may also assist in this conversion.

6. **Combine the Findings**:
- Therefore, the two bacteria involved in the two-step conversion of ammonia to nitrate are **Nitrosomonas** (for the first step) and **Nitrobacter** (for the second step).

7. **Select the Correct Answer**:
- Based on the options provided, the correct answer is **Nitrosomonas and Nitrobacter**.

### Final Answer:
The bacteria involved in the two-step conversion of NH3 into nitrate are **Nitrosomonas and Nitrobacter**.

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