Bacillus cerus bacteria. Coloured scanning electron micrograph (SEM) of a colony of Bacillus cerus bacteria. These common, rod-shaped Gram- type-positive bacteria are saprotrophs, organisms that feed and grow on dead and decaying organic material. They are found in soil, water, air and on vegetation. As here, the Bacillus bacteria often form chains. B. cerus can cause food poisoning. Magnification: x3,700 at 6x7cm size. x6000 at 4x5 inch size.