Name one aerobic and one anaerobic nitrogen fixing bacteria.

Explanation

**Step-by-Step Solution:**

1. **Understanding Nitrogen Fixation**: Nitrogen-fixing bacteria are microorganisms that can convert atmospheric nitrogen (N₂) into ammonia (NH₃), which can be utilized by plants. This process is essential for the nitrogen cycle and helps in enriching soil fertility.

2. **Aerobic Nitrogen-Fixing Bacteria**: These bacteria require oxygen to survive and carry out their nitrogen-fixing activities. One well-known aerobic nitrogen-fixing bacterium is **Azotobacter**. Another example is **Beijerinckia**.

3. **Anaerobic Nitrogen-Fixing Bacteria**: In contrast, anaerobic bacteria do not require oxygen and can fix nitrogen in its absence. A common anaerobic nitrogen-fixing bacterium is **Clostridium**. Another example is **Bacillus**. Additionally, **Rhodospirillum** is also recognized as an anaerobic nitrogen-fixing bacterium.

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