8 Why are bacteria needed in the nitrogen cycle. Whereas other organisms are incapable of trapping or utilizing the atmospheric nitrogen. Rho6science Licensed For Non Commercial Use Only Nitrogen Cycle Notes Nitrogen Cycle Science Notes Nitrogen Bacteria in the soil or bacteria found in nodules of legumes Nitrogen is a necessary component of life as plants need it to grow and animals need it to create DNA. . The bacteria a necessary part of the nitrogen cycle because the living things cannot use atmospheric nitrogen. Other living things cannot use atmospheric nitrogen. 11 Why are. In the nitrogen fixation process nitrogen fixing bacteria converts the N_2 in the atmosphere into NH_3 ammonia. The speed of decomposition is the key to keeping the nitrogen cycle moving as the majority of fixated nitrogen comes from bacteria breaking down dead matter and feces. In the nitrogen cycle bacteria are very important because atmospheri...