A non -legume , symbiotic nitrogen fixing bacterium is

Options

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

Answer

To answer the question "A non-legume, symbiotic nitrogen-fixing bacterium is," we will analyze the options provided and identify the correct answer step by step.

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**:
- Nitrogen is essential for plants as it is a key component of amino acids, proteins, and nucleic acids. However, atmospheric nitrogen (N₂) cannot be directly utilized by plants.
- Certain bacteria can convert atmospheric nitrogen into a form that plants can absorb and use, a process known as nitrogen fixation.

2. **Identifying the Types of Nitrogen-Fixing Bacteria**:
- There are two main types of nitrogen-fixing bacteria: **symbiotic** and **free-living**.
- **Symbiotic bacteria** form a mutual relationship with plants, while **free-living bacteria** do not require a host plant for their nitrogen-fixing activity.

3. **Analyzing the Options**:
- **Option A: Rhizobium**:
- Rhizobium is a well-known symbiotic nitrogen-fixing bacterium but it specifically associates with legume plants. Therefore, it does not fit the requirement of being a non-legume symbiotic nitrogen-fixing bacterium.
- **Option B: Azotobacter**:
- Azotobacter is a free-living nitrogen-fixing bacterium and does not form a symbiotic relationship with any plants. Hence, it is not the answer.
- **Option C: Frankia**:
- Frankia is a symbiotic nitrogen-fixing bacterium that associates with non-legume plants, such as alder trees. This fits the criteria of the question.
- **Option D: Clostridium**:
- Clostridium is also a free-living nitrogen-fixing bacterium and does not form symbiotic relationships with plants, making it an incorrect choice.

4. **Conclusion**:
- Based on the analysis, the correct answer is **Option C: Frankia**, as it is a non-legume, symbiotic nitrogen-fixing bacterium.

### Final Answer:
**Frankia**