Symbiotic microorgainsm is

Options

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

Answer

**Step-by-Step Solution:**

1. **Understanding Symbiotic Microorganisms**:
- Symbiotic microorganisms are organisms that live in close association with a host plant, often providing benefits to each other.

2. **Evaluating the Options**:
- **Option A: Clostridium**:
- Clostridium is a genus of rod-shaped, usually gram-positive bacteria that are free-living in soil and water. Since it does not form a symbiotic relationship with plants, this option is incorrect.

- **Option B: Azotobacter**:
- Azotobacter is also a free-living nitrogen-fixing bacterium. It does not form symbiotic relationships with plants, making this option incorrect as well.

- **Option C: Rhizobium**:
- Rhizobium is known for forming symbiotic relationships with leguminous plants. It resides in the root nodules of these plants and helps in fixing atmospheric nitrogen into ammonia, which the plant can use. This mutualistic relationship makes Rhizobium the correct answer.

- **Option D: Chromatium**:
- Chromatium is a genus of photoautotrophic gram-negative bacteria that are found free-living in water. Similar to the previous options, it does not form a symbiotic relationship with plants, thus this option is also incorrect.

3. **Conclusion**:
- After evaluating all the options, the correct answer to the question "Symbiotic microorganism is" is **Rhizobium**.

**Final Answer**: Rhizobium

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