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, we need to identify a Gram-negative bacterium that is pleomorphic and promotes plant growth. Let's break down the solution step by step:

### Step 1: Understand the Characteristics Required
- **Gram-negative bacterium**: This refers to bacteria that do not retain the crystal violet stain used in the Gram staining protocol, which means they have a thin peptidoglycan layer and an outer membrane.
- **Pleomorphic**: This means the bacterium can change its shape or form under different conditions.
- **Plant growth-promoting**: The bacterium should have a beneficial effect on plant growth, often through mechanisms like nitrogen fixation.

### Step 2: Analyze the Options
- We need to look at the options provided (not listed here) to find a bacterium that fits all the criteria mentioned above.

### Step 3: Identify Rhizobium
- **Rhizobium** is a well-known Gram-negative bacterium that forms a symbiotic relationship with leguminous plants (like lentils, peas, and groundnuts).
- It is pleomorphic because it can exist in different forms: as a rod shape when free-living and as swollen structures called bacteroids when in root nodules of plants.

### Step 4: Explain the Symbiotic Relationship
- In this mutualistic relationship, Rhizobium provides nitrogen to the plants by fixing atmospheric nitrogen into a form that plants can use, while the plants provide nutrients and shelter to the bacteria.

### Step 5: Conclusion
- Based on the characteristics and the analysis, the correct answer is **Rhizobium** (Option B), which is a Gram-negative, pleomorphic bacterium that promotes plant growth.

### Final Answer:
The example of a plant growth-promoting Gram-negative bacterium that is pleomorphic in nature is **Rhizobium**.

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