Which of the following is a bacterium involved in denitrification?

Options

A. Nitrococcus
B. Nitrosomonas
C. Pseudomonas
D. Nitrobacter

Answer

To solve the question "Which of the following is a bacterium involved in denitrification?" we need to analyze the options provided and understand the process of denitrification.

### Step-by-Step Solution:

1. **Understand Denitrification**:
- Denitrification is the process by which nitrate ions (NO3-) are converted into nitrogen gas (N2), which is released into the atmosphere. This process is crucial for the nitrogen cycle as it helps in reducing the amount of nitrates in the soil and returning nitrogen to the atmosphere.

2. **Identify the Bacteria Involved**:
- Various bacteria are involved in denitrification. Common denitrifying bacteria include:
- **Pseudomonas denitrificans**: Known to play a significant role in denitrification.
- **Thiobacillus denitrificans**: Another bacterium that participates in this process.

3. **Analyze the Options**:
- **Nitrococcus**: Primarily involved in nitrification, not denitrification.
- **Nitrosomonas**: Also involved in nitrification, converting ammonia to nitrite.
- **Pseudomonas**: Specifically, Pseudomonas denitrificans is involved in denitrification.
- **Nitrobacter**: Involved in nitrification, converting nitrite to nitrate.

4. **Select the Correct Answer**:
- Based on the analysis, the only bacterium from the options that is involved in denitrification is **Pseudomonas**.

### Final Answer:
The correct answer is **Pseudomonas**.

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