Pigmentation of Serratia marcescens and spectral properties of prodigiosin

Pigmentation of Serratia marcescens depends on the composition of the cultivation medium. The cultures grown on glycerol-peptone medium and on the medium with acetate are red and yellow (yellowish orange), respectively, with the color depending on the ambient pH. S. marcescens cells growth on glycerolpeptone medium (visually of red color) contain two forms of prodigiosin: the “red” and “yellow” ones with absorption maxima at 535 and 460–470 nm, respectively. The absorption spectrum of prodigiosin in the native pigment-protein complex was different from the spectrum of the pigment dissolved in ethanol and resembled that of the cell suspension in the presence of an additional absorption maximum at 500 nm. Prodigiosin sensitivity to low-intensity visible light depended on the state of co-solubilized protein. The sensitivity of prodigiosin in the complex with a native protein is similar to the pigment photosensitivity in the composition of an intact bacterial cell. Prodigiosin extracted under denaturation conditions was less sensitive to illumination. Both the “red” and the “yellow” form of prodigiosin in solution fluoresced at 560–565 nm; the in vivo fluorescence of the red pigment form was more marked.