What is the name of the bacteria involved in nitrogen fixation in legumes?

The bacteria involved in nitrogen fixation in legumes is known as Rhizobium. This group of bacteria forms symbiotic relationships with the roots of leguminous plants, such as beans and peas. In this symbiosis, Rhizobium enter the root cells of the legume, leading to the formation of specialized structures called nodules. Within these nodules, the bacteria convert atmospheric nitrogen (N2), which is inert and not directly usable by plants, into ammonia (NH3) through a process called biological nitrogen fixation. This ammonia can then be assimilated by the plant into amino acids and other nitrogenous compounds, thus enhancing the plant's growth and productivity while simultaneously improving soil fertility.

The other options refer to different types of bacteria or pathogens that do not participate in nitrogen fixation in legumes. Bacillus thuringiensis is known for its role as a biocontrol agent against insect pests. E. coli is primarily associated with the intestines of humans and animals and is not involved in nitrogen fixation. Phytophthora is a genus of water mold pathogens known for causing diseases in various plants, including root rot, rather than contributing to nitrogen fixation.