Which one of the following bacteria is not connected with nitrogen fixation?

Options

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

Answer

To determine which bacteria is not connected with nitrogen fixation, we can analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understand Nitrogen Fixation**:
- Nitrogen fixation is the process by which atmospheric nitrogen (N₂) is converted into ammonia (NH₃) or related compounds in soil. This process is crucial for making nitrogen available to plants.

2. **Evaluate Each Option**:
- **Option A: Azotobacter**
- Azotobacter is a free-living nitrogen-fixing bacterium that converts atmospheric nitrogen into ammonia. Therefore, it is involved in nitrogen fixation.
- **Option B: Nitrosomonas**
- Nitrosomonas is a gram-negative bacterium that is involved in the nitrification process, where it oxidizes ammonia into nitrite. It does not fix nitrogen; hence, it is not connected with nitrogen fixation.
- **Option C: Francia**
- Francia is a genus of bacteria that also participates in nitrogen fixation, particularly in symbiotic relationships with plants. Thus, it is involved in nitrogen fixation.
- **Option D: Rhizobium**
- Rhizobium is well-known for forming symbiotic relationships with legumes, where it fixes atmospheric nitrogen into a form that plants can use. Therefore, it is also involved in nitrogen fixation.

3. **Conclusion**:
- After evaluating all options, **Option B: Nitrosomonas** is the only bacterium that is not connected with nitrogen fixation. It is primarily involved in the nitrification process rather than directly fixing nitrogen.

### Final Answer:
**The bacteria that is not connected with nitrogen fixation is Nitrosomonas (Option B).**

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