DNA. False-colour transmission electron micrograph (TEM) of the bacterium Escherichia coli surrounded by its DNA. The bacterium was treated with an enzyme to weaken its cell wall and then placed in water, causing its DNA to be ejected. The DNA is visible as the gold-coloured fibrous mass lying around the green bacterial shell. The total length of DNA is 1.5 millimetres, 1000 times the length of the bacterium itself. E. coli is a usually harmless inhabitant of the human intestinal tract. It is an important laboratory organism and is widely used in biotechnology research. Magnification: x12,500 at 6x4.5 cm size.