An example of plant growth promoting Gram - negative bacterium, which is pleomorphic in nature is

Options

A. Pseudomonas
B. Rhizobium
C. Aspergillus
D. Azospirillum

Answer

To solve the question regarding an example of a plant growth-promoting Gram-negative bacterium that is pleomorphic in nature, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: We need to identify a Gram-negative bacterium that promotes plant growth and exhibits pleomorphic characteristics.

2. **Review the Options**: The options provided are:
- Pseudomonas
- Rhizobium
- Aspergillus
- Azospirillum

3. **Analyze Each Option**:
- **Pseudomonas**: This is a genus of bacteria known for causing infections. While it can live in soil and water, it is not specifically known for being pleomorphic. Therefore, this option is incorrect.

- **Rhizobium**: This bacterium is known for its symbiotic relationship with legumes. It can exist in two forms: as a rod-shaped bacterium in free-living conditions and as swollen bacteroids when associated with the roots of leguminous plants. This characteristic of existing in more than one form makes it pleomorphic. Additionally, it is a Gram-negative bacterium that promotes plant growth by fixing nitrogen. Thus, this is the correct option.

- **Aspergillus**: This is a genus of fungi, not bacteria. Therefore, it cannot be the correct answer.

- **Azospirillum**: This bacterium also promotes plant growth and can fix nitrogen, but it is not known for being pleomorphic. Hence, this option is also incorrect.

4. **Conclusion**: Based on the analysis, the correct answer is **Rhizobium**, as it is a Gram-negative bacterium that is pleomorphic and promotes plant growth.

### Final Answer:
**Rhizobium**

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