A non -photosynthetic aerobic nitrogen fixing soil bacterium is

Options

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

Answer

To solve the question "A non-photosynthetic aerobic nitrogen-fixing soil bacterium is," we will analyze each of the given options step by step.

### Step 1: Understand the Requirements
We need to identify a bacterium that meets the following criteria:
- Non-photosynthetic
- Aerobic
- Nitrogen-fixing

### Step 2: Analyze Each Option
1. **Rhizobium**:
- Rhizobium is known to form a symbiotic relationship with leguminous plants.
- It is aerobic and can fix nitrogen, but it is not considered non-photosynthetic because it relies on the host plant for nutrients.
- **Conclusion**: Not the correct answer.

2. **Clostridium**:
- Clostridium is an anaerobic bacterium, meaning it does not require oxygen for growth.
- It does not fit the aerobic requirement.
- **Conclusion**: Not the correct answer.

3. **Azotobacter**:
- Azotobacter is an aerobic bacterium that can fix nitrogen from the atmosphere.
- It is non-photosynthetic and can utilize carbon dioxide for its metabolic processes.
- **Conclusion**: This option meets all the criteria.

4. **Klebsiella**:
- Klebsiella is generally considered an anaerobic bacterium and is known for being a pathogenic organism.
- It does not meet the aerobic requirement.
- **Conclusion**: Not the correct answer.

### Step 3: Final Answer
Based on the analysis, the correct answer is **Azotobacter**, as it is a non-photosynthetic, aerobic, nitrogen-fixing soil bacterium.