Which of the following is non-symbiotic ?

Options

A. Azotobacter
B. Nostoc
C. Rhizobium
D. Frankia

Answer

To determine which of the following is non-symbiotic, we need to analyze each option provided in the question.

1. **Azotobacter**: This is a free-living nitrogen-fixing bacterium. It does not form symbiotic relationships with plants or other organisms. Instead, it exists independently in the soil, fixing nitrogen from the atmosphere.

2. **Nostoc**: This is a cyanobacterium that can form symbiotic relationships, particularly with aquatic plants like Azolla. It is known for its ability to fix nitrogen in a symbiotic manner.

3. **Rhizobium**: This bacterium is well-known for forming symbiotic relationships with leguminous plants. It resides in root nodules of these plants and helps in nitrogen fixation, making it a classic example of a symbiotic bacterium.

4. **Francia**: Similar to Rhizobium, Francia is also a symbiotic bacterium that forms associations with non-leguminous plants, particularly in root nodules. It also contributes to nitrogen fixation in these plants.

Based on this analysis, the only non-symbiotic organism among the options is **Azotobacter**.

**Final Answer**: The non-symbiotic organism is **Azotobacter**.