Option 1: Clostridium. Clostridium is a genus of bacteria that includes various species, some of which can cause diseases in animals and humans. They are known for their ability to form endospores, which are resistant structures that allow them to survive harsh conditions. While Clostridium can be beneficial in certain industries such as biotechnology and food processing, it does not have a direct role in improving soil fertility.

Option 2: Rhizobium. Rhizobium is a genus of bacteria that forms a symbiotic relationship with leguminous plants. These bacteria colonize the roots of plants and convert atmospheric nitrogen into a usable form, known as nitrogen fixation. This process increases the nitrogen content in the soil, enhancing its fertility. Rhizobium is essential for the growth and development of leguminous plants and plays a crucial role in improving soil fertility.

Option 3: Salmonella. Salmonella is a genus of bacteria that is well-known for causing foodborne illnesses in humans and animals. It does not contribute to soil fertility improvement.

Option 4: Staphylococcus. Staphylococcus is a genus of bacteria that includes various species, some of which can cause infections in humans. It does not have