Which one of the following is associated with denitrification ?

Options

A. Rhizobium
B. Thiobacillus
C. Clostridium
D. Azotobacter

Answer

To solve the question "Which one of the following is associated with denitrification?" we will analyze the options provided and identify which organism is known for its role in the denitrification process.

### Step-by-Step Solution:

1. **Understand Denitrification**:
- Denitrification is the process by which nitrates (NO3-) and nitrites (NO2-) are converted into nitrogen gas (N2) or, to a lesser extent, nitrous oxide (N2O). This process is crucial for the nitrogen cycle as it helps to return nitrogen to the atmosphere.

2. **Examine the Options**:
- **Option 1: Rhizobium**: This genus is primarily known for nitrogen fixation in symbiotic relationships with legumes, not denitrification.
- **Option 2: Thiobacillus**: This genus includes species that can perform denitrification, particularly Thiobacillus denitrificans, which is known for converting nitrates to nitrogen gas.
- **Option 3: Clostridium**: While some Clostridium species can fix nitrogen, they are not primarily associated with denitrification.
- **Option 4: Azotobacter**: This genus is also known for nitrogen fixation rather than denitrification.

3. **Identify the Correct Answer**:
- Based on the analysis, the organism most associated with denitrification among the options provided is **Thiobacillus**.

4. **Conclusion**:
- Therefore, the correct answer to the question is **Option 2: Thiobacillus**.