Which of the following bacteria can live symbiotically?

Options

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

Explanation

**Step-by-Step Solution:**

1. **Understanding Symbiotic Relationships**: A symbiotic relationship is an association between two different organisms where both benefit from the interaction. In the context of bacteria, this often involves bacteria living in close association with plants.

2. **Identifying the Bacteria**: The question provides four types of bacteria:
- Rhizobium
- Nitrosomonas
- Azotobacter
- Clostridium

3. **Analyzing Each Bacterium**:
- **Rhizobium**: This bacterium is known for its ability to fix nitrogen. It forms a symbiotic relationship with leguminous plants (like gram, pea, and bean) by converting atmospheric nitrogen into ammonia, which the plants can use. This makes Rhizobium a symbiotic bacterium.

- **Nitrosomonas**: This bacterium is involved in nitrification, which is a process that converts ammonia into nitrites. It does not form a symbiotic relationship with plants; instead, it is a free-living bacterium.

- **Azotobacter**: This bacterium also fixes nitrogen but does so independently in the soil and does not form a symbiotic relationship with plants. It is considered a free-living nitrogen-fixing bacterium.

- **Clostridium**: Similar to Azotobacter, Clostridium is a free-living bacterium that can fix nitrogen but does not engage in a symbiotic relationship with plants.

4. **Conclusion**: Among the given options, only Rhizobium forms a symbiotic relationship with plants, specifically leguminous plants, making it the correct answer.

**Final Answer**: Rhizobium is the bacterium that can live symbiotically.

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