Which of these bacteria is present in the roots of leguminous plants such as peas and helps in the process of nitrogen fixation?

Options

A. Xanthomonas
B. Lactobacillus
C. Nitrobacter
D. Rhizobium

Answer

**Step-by-Step Solution:**

1. **Understand the Question**: The question asks which bacteria is found in the roots of leguminous plants, like peas, and assists in nitrogen fixation.

2. **Identify the Options**: The options provided are:
- Xanthomonas
- Lactobacillus
- Nitrobacter
- Rhizobium

3. **Define Nitrogen Fixation**: Nitrogen fixation is the process of converting atmospheric nitrogen (N₂) into ammonia (NH₃), which plants can use. This process is essential because plants cannot directly utilize atmospheric nitrogen.

4. **Different Types of Nitrogen-Fixing Bacteria**: There are two types of nitrogen-fixing bacteria:
- Free-living nitrogen-fixing bacteria
- Symbiotic nitrogen-fixing bacteria

5. **Identify Symbiotic Nitrogen Fixing Bacteria**: Among the options, Rhizobium is known to form a symbiotic relationship with leguminous plants. It lives in the root nodules of these plants and helps in nitrogen fixation.

6. **Eliminate Incorrect Options**:
- **Xanthomonas**: This is a genus of bacteria that causes plant diseases and is not involved in nitrogen fixation.
- **Lactobacillus**: This bacteria is involved in fermentation processes, such as converting milk into curd, not nitrogen fixation.
- **Nitrobacter**: This bacteria is involved in nitrification, which is a different process from nitrogen fixation.

7. **Conclusion**: The correct answer is **Rhizobium**, as it is the bacteria that resides in the roots of leguminous plants like peas and is responsible for nitrogen fixation.

**Final Answer**: Rhizobium

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