Nitrogen fixing aerobic photosynthetic and Gram (-) bacteria are

Options

A. Archaebacteria
B. Cyanobacteria
C. Chlorobacteria
D. Rickettsiae.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question:**
The question asks for an example of bacteria that are nitrogen-fixing, aerobic, photosynthetic, and Gram-negative.

2. **Defining Key Terms:**
- **Nitrogen-fixing bacteria:** These bacteria convert atmospheric nitrogen (N₂) into a form that plants can use, such as ammonia (NH₃).
- **Aerobic bacteria:** These bacteria require oxygen for their survival and growth.
- **Photosynthetic bacteria:** These bacteria can convert light energy into chemical energy through photosynthesis.
- **Gram-negative bacteria:** These bacteria have a specific cell wall structure that does not retain the crystal violet stain used in the Gram staining procedure.

3. **Identifying Candidates:**
- We need to find a bacterium that meets all these criteria.
- Common examples of nitrogen-fixing bacteria include Rhizobium, Azotobacter, and cyanobacteria.

4. **Analyzing Cyanobacteria:**
- Cyanobacteria are known to be photosynthetic and can fix nitrogen.
- They are also classified as Gram-negative bacteria.
- Examples of cyanobacteria include Anabaena and Nostoc, which are known for their nitrogen-fixing capabilities.

5. **Conclusion:**
Based on the analysis, the correct answer to the question is **Cyanobacteria**. They are nitrogen-fixing, aerobic, photosynthetic, and Gram-negative bacteria.

6. **Final Answer:**
The nitrogen-fixing aerobic photosynthetic and Gram-negative bacteria are **Cyanobacteria**.

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