which of the following is an autotrophic bacterium?

Options

A. Rhizobium
B. Azotobacter
C. Nitrobacter
D. Clostridium.

Answer

To determine which of the following is an autotrophic bacterium, we will analyze each option provided:

1. **Rhizobium**:
- Rhizobium is known as a diazotropic bacterium that forms a symbiotic association with the root nodules of leguminous plants.
- While it plays a crucial role in nitrogen fixation, it does not synthesize its own food and is therefore not classified as an autotrophic bacterium.
- **Conclusion**: Incorrect option.

2. **Escherichia coli (Esotobacter)**:
- Escherichia coli is a genus of free-living diazotropic bacteria, typically found in neutral to alkaline environments.
- Similar to Rhizobium, it does not synthesize its own food and is not considered autotrophic.
- **Conclusion**: Incorrect option.

3. **Nitrobacter**:
- Nitrobacter is a genus of rod-shaped, gram-negative bacteria that are classified as chemo-autotrophic bacteria.
- They obtain energy through the oxidation of ammonia to nitrite and subsequently convert nitrite to nitrate, which can be utilized by plants.
- Since they can synthesize their own food using chemical energy, they are indeed autotrophic.
- **Conclusion**: Correct option.

4. **Clostridium**:
- Clostridium, specifically Clostridium botulinum, is a soil-dwelling heterotrophic bacterium.
- It metabolizes food strictly through fermentation and does not synthesize its own food.
- **Conclusion**: Incorrect option.

**Final Answer**: The correct option is **Nitrobacter**, which is an autotrophic bacterium.