Studies on the biosynthesis of prodigiosin in Serratia marcescens

Abstract

Prodigiosin, the blood-red pigment produced by Serratia marcescens, is a linear tripyrrole. Through a series of isotope incorporation experiments, it has been possible to show that this pigment, although a pryrrolic compound, is not closely related to the porphyrins biosynthetically. It has been demonstrated that δ-aminolevulinic acid a specific precursor of porphyrins, is capable of penetrating the membrane of Serratia marcescens but is not used in the formation of prodigiosin.The possibility that prodigiosin may be derived from four proline units has been studied and found to be untenable. The carboxyl carbon of proline is probably incorporated, as a single carbon unit, into the dipyrrolic precursor of prodigiosin produced by Serratia marcescens mutant 9-3-3. Incorporation experiments utilizing [14C]proline (uniformly labeled), [1-14C]proline, and [2-14C]proline into both prodigiosin and its dipyrrolic precursor, indicate that C-2, and perhaps the entire ring, of proline is utilized mainly in the formation of the 2-methyl-3-amylpyrrole part of prodigiosin. Hydroxyproline is not utilized in the formation of ring II of prodigiosin.On the basis of [2-14C]glycine incorporation into both prodigiosin and its dipyrrolic precursor, it is apparent that the methyl carbon atom of glycine is incorporated with equal efficiency into both halves of the prodigiosin molecule. It is, however, probable that rings I and II are formed by a different mechanism than ring III.