Bacteria have adapted to live in many niches; from the environmental bacteria that live in the soil and the seas, to the highly specialised intracellular bacteria that rely exclusively on their surrounding host for nutrients. While all bacteria face challenges in adapting their environment to suit them, intracellular bacteria face a particularly interesting challenge, as they must adapt to the conditions inside a living creature without killing their host.
All living organisms require a source of carbon, nitrogen and oxgyen in order to survive. Most organisms, particular the multicellular ones, prefer to use glucose or glycogen as a source of carbon, but some bacteria have found alternative ways of surviving. The bacteria Legionella pneumophila, which can live inside human or amoeba cells and is the cause of Legionnaires disease, gets its energy sources from the amino acids that make up proteins. Essentially, it lives on the Atkins diet, consuming high levels of protein and much lower levels of carbs.