As we know the nitrogen cycle is composed of several stages and is a very essential part of every organism as is present in the DNA. Most of the nitrogen is atmospheric N2 and is not available for living organisms, here the bacterias play an important role in fixating Nitrogen so is available for other organisms, therefore often is a limiting resource. Now Most of the nitrogen that comes into the earth is through bacteria, although it can happen naturally at a very slow rate, so we can say that the nitrogen cycle wouldn't exist without bacteria.