False-colour transmission electron micrograph (TEM) of Bacillus megaterium, a Gram-positive, aerobic positive species of bacteria, in the process of cell division. Here, in this late phase of replication, the cell walls (at centre, pink) separating the two pairs of sister cells, has almost completely formed. Bacteria do not contain a nucleus, and the DNA - genetic material - is scattered. Dense granules (green) are visible. Of the 34 species of Bacillus listed in 1992, only 2, B. anthracis (the anthrax bacillus) & B. cereus, are significant human pathogens. Magnification: x6800 at 6x7cm size.