Which of the following does NOT conduct nitrogen fixation?

• A. Azotobacter
• B. Rhizobium bacteria
• C. Escherichia coli
• D. Cyanobacteria

Answer: (C)

Verified step by step guidance

1. Understand the concept of nitrogen fixation: Nitrogen fixation is the process by which certain organisms convert atmospheric nitrogen (N₂) into ammonia (NH₃), which can be used by plants. This process is essential for the nitrogen cycle and is carried out by specific bacteria and archaea.
2. Identify the organisms listed in the problem: Azotobacter, Rhizobium bacteria, Escherichia coli, and Cyanobacteria. Determine which of these are known nitrogen-fixing organisms.
3. Recall that Azotobacter is a free-living nitrogen-fixing bacterium found in soil. It plays a role in converting atmospheric nitrogen into ammonia without forming symbiotic relationships.
4. Understand that Rhizobium bacteria are symbiotic nitrogen-fixing bacteria that form nodules on the roots of leguminous plants, facilitating nitrogen fixation in a mutualistic relationship.
5. Note that Escherichia coli is a common gut bacterium and does not participate in nitrogen fixation. Cyanobacteria, on the other hand, are photosynthetic bacteria capable of nitrogen fixation, often found in aquatic environments. Therefore, Escherichia coli does NOT conduct nitrogen fixation.