The first nif genes were isolated from

Options

A. Klebsiella aerogenes
B. Klebsiella oxytoa
C. Klebsiella pneumonia
D. Klebsiella granulonatis

Answer

### Step-by-Step Solution

1. **Understanding NIF Genes**:
- NIF genes are specific genes that are involved in nitrogen fixation. They encode enzymes that facilitate the conversion of atmospheric nitrogen (N₂) into ammonia (NH₃), which can be utilized by plants.

2. **Identifying the Source of NIF Genes**:
- The question asks where the first NIF genes were isolated from. The options provided are various species of Klebsiella.

3. **Analyzing the Options**:
- **Klebsiella aerogenes**: This is a species of bacteria, but it is not known for being the source of the first NIF genes.
- **Klebsiella oxytoca**: Similar to K. aerogenes, this species is not recognized as the source of the first NIF genes.
- **Klebsiella pneumoniae**: This species is known for its role in nitrogen fixation and is recognized as the first source from which NIF genes were isolated.
- **Klebsiella granulonatus**: This species is also not known for being the source of the first NIF genes.

4. **Conclusion**:
- Based on the analysis, the correct answer is **Klebsiella pneumoniae**. This species contains a total of 20 NIF genes and is classified as a free-living anaerobic nitrogen-fixing bacterium.

### Final Answer:
The first NIF genes were isolated from **Klebsiella pneumoniae**.

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