List any two bacteria which play a role in biological nitrogen fixation.

Explanation

### Step-by-Step Solution:

1. **Understand Biological Nitrogen Fixation**:
- Biological nitrogen fixation is the process through which atmospheric nitrogen (N₂) is converted into ammonia (NH₃) by living organisms, primarily bacteria. This process is essential because plants cannot utilize atmospheric nitrogen directly.

2. **Identify Types of Nitrogen-Fixing Bacteria**:
- There are two main types of nitrogen-fixing bacteria:
- **Symbiotic Nitrogen-Fixing Bacteria**: These bacteria form a symbiotic relationship with plants, particularly legumes.
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