Which of the following bacteria can fix nitrogen for plants such as clover and beans ?

Rhizobium can fix nitrogen for plants like clover and beans. Rhizobia are soil bacteria that induce the formation of special structures, called nodules, on the roots of their host plants. Inside these nodules, the rhizobia fix nitrogen by converting dinitrogen (the nitrogen gas that makes up 80% of the air one breathe) into ammonia. Ammonia is toxic, so it is rapidly assimilated into organic compounds, most of which the bacteria pass to the plant to fulfill its nutritional need for nitrogen.