The `N_(2)` -fixing bacterium associated with root nodules of legumes is known as

Options

A. Azotobacter
B. Nitrobacter
C. Lactobacillus
D. Rhizobium

Answer

To answer the question about the nitrogen-fixing bacterium associated with root nodules of legumes, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**:
- Nitrogen fixation is the process by which nitrogen (N₂) from the atmosphere is converted into ammonia (NH₃) or related compounds in soil and water. This process is crucial for plants as they cannot utilize atmospheric nitrogen directly.

2. **Identifying the Symbiotic Relationship**:
- Legumes, which are a type of plant, form a symbiotic relationship with certain bacteria that can fix nitrogen. This means that the bacteria live in close association with the roots of the legumes and provide them with nitrogen in a usable form.

3. **Recognizing the Bacteria Involved**:
- The primary bacterium known for this symbiotic relationship with legumes is called **Rhizobium**. This bacterium forms nodules on the roots of leguminous plants, where it converts atmospheric nitrogen into a form that the plant can absorb.

4. **Eliminating Incorrect Options**:
- The question may provide multiple-choice options. Common nitrogen-fixing bacteria include:
- **Azotobacter**: A free-living nitrogen-fixing bacterium, not associated with legumes.
- **Nitrobacter**: A genus of bacteria involved in the nitrification process, not nitrogen fixation.
- **Lactobacillus**: A genus of bacteria primarily involved in fermentation, not nitrogen fixation.
- Since these options are not associated with the symbiotic relationship with legumes, they can be eliminated.

5. **Conclusion**:
- The correct answer to the question is **Rhizobium**, as it is the nitrogen-fixing bacterium that forms root nodules in legumes.

### Final Answer:
The nitrogen-fixing bacterium associated with root nodules of legumes is known as **Rhizobium**.

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