Symbiotic nitrogen fixing bacteria belong to

Options

A. Xanthomonas
B. Acetobacteria
C. Pseudomonas
D. Rhizobium.

Answer

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**:
- Nitrogen in the atmosphere is abundant but in a form (N2) that plants cannot use directly. It needs to be converted into a usable form, such as ammonia (NH3).

2. **Role of Nitrogen-Fixing Bacteria**:
- Certain bacteria have the ability to convert atmospheric nitrogen into ammonia. These bacteria are known as nitrogen-fixing bacteria.

3. **Symbiotic Relationship**:
- Some nitrogen-fixing bacteria form a symbiotic relationship with plants, particularly leguminous plants (like peas, beans, and clover). In this relationship, the bacteria provide nitrogen to the plants, and in return, they receive shelter and nutrients.

4. **Identifying Symbiotic Nitrogen-Fixing Bacteria**:
- Among the options given:
- **Xanthomonas**: A genus of bacteria that are plant pathogens, not known for nitrogen fixation.
- **Acetobacteria**: Generally involved in the fermentation process, not primarily known for symbiotic nitrogen fixation.
- **Pseudomonas**: A diverse group of bacteria, some of which can fix nitrogen, but they are not typically symbiotic with plants.
- **Rhizobium**: A genus of bacteria that specifically forms nodules on the roots of leguminous plants and is well-known for its role in symbiotic nitrogen fixation.

5. **Conclusion**:
- The correct answer to the question "Symbiotic nitrogen-fixing bacteria belong to" is **Rhizobium**.

### Final Answer:
- **Rhizobium** (Option 4) is the correct answer.

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