Find the group of bacteria in which all are nitrogen fixing :

Options

A. Nitrosomonas, Streptococcus, Lactobacillus
B. rhizobium, Azotobacter, Nostoc
C. Nitrobacter, Streptobacillus, Lactobacillus
D. Clostridium, Rhizobium, Lactobacillus

Answer

To find the group of bacteria in which all are nitrogen-fixing, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Nitrogen Fixation**: Nitrogen fixation is the process by which certain bacteria convert atmospheric nitrogen (N2) into ammonia (NH3), which can then be used by plants.

2. **Identify the Options**: The question provides several groups of bacteria as options. We need to analyze each group to determine if all members are nitrogen-fixing.

3. **Evaluate the Options**:
- **Option 1**: Natrosomonas, Streptococcus, and Lactobacillus.
- Natrosomonas is not a nitrogen-fixing bacterium.
- Streptococcus is primarily known for its role in fermentation and does not fix nitrogen.
- Lactobacillus is also not involved in nitrogen fixation; it is used in fermentation.
- **Conclusion**: Not all are nitrogen-fixing.

- **Option 2**: Rhizobium, Azotobacter, and Blue-green algae.
- Rhizobium forms nodules in the roots of leguminous plants and is a well-known nitrogen-fixing bacterium.
- Azotobacter is a free-living nitrogen-fixing bacterium.
- Blue-green algae (like Nostoc and Anabaena) are also capable of nitrogen fixation.
- **Conclusion**: All are nitrogen-fixing.

- **Option 3**: (not specified in the transcript).
- **Option 4**: (not specified in the transcript).

4. **Select the Correct Option**: Based on the evaluation, Option 2 (Rhizobium, Azotobacter, and Blue-green algae) is the group where all members are nitrogen-fixing bacteria.

### Final Answer:
The group of bacteria in which all are nitrogen-fixing is **Option 2: Rhizobium, Azotobacter, and Blue-green algae**.

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