Biosynthesis of prodigiosin, a secondary metabolite of Serratia marcescens

Prodigiosenes (prodigiosin and prodigiosin-like pigments) are known to be synthesized by only one genus of Eubacteriales and by two genera of Actinomycetales. Biosynthesis by Serratia marcescens occurs over a relatively narrow range of temperatures, although the bacteria grow over a broad range. When cultures of S. marcescens were incubated at 27 C in 1.0% casein hydrolysate, viable count and protein attained maximal values within 24 to 48 h, whereas prodigiosin did not reach a maximum until 96 h. The greatest amount of pigment was synthesized when cultures were in the senescent phase of growth. Suspensions of nonproliferating bacteria incubated at 27 C in only L-alanine also synthesized prodigiosin, although at a slower rate than growing cultures. Kinetics of growth for the wild-type, red S. marcescens and a white mutant were identical when incubated at 27 C, but the wild type produced abundant pigment. These results plus other data obtained from the literature suggest that prodigiosin is a secondary metabolite. The importance of this proposal to understanding the function of prodigiosin in S. marcescens is discussed.