Serratia marcesens is a Gram-negative, rod-shaped bacterium that is commonly found in soil, water, on plants and in animals and thrives in damp conditions. This organism is well known for its production of the blood red pigment, prodigiosin. Production of prodigiosin can be influenced by several variables, including temperature, nutrient media and ultraviolet light exposure. The metabolic pathways that are involved in the production of the pigment are numerous and complex. Mutations to any one of the pathways can lead to a loss of pigment production. This photo shows a Serratia marcesens colony from a mutated strain in which pigment production has decreased. Instead of a solid red colony, the bacteria exhibit beautiful swirls of red and orange on a white background.