Effect of Iron and Salt on Prodigiosin Synthesis in Serratia marcescens
Serratia marcescens wild-types ATCC 264 and Nima grew but did not synthesize prodigiosin in a glycerol-alanine medium containing 10 ng of Fe per ml. Wild-type 264 required the addition of 0.2 μg of Fe per ml for maximal growth and prodigiosin synthesis; Nima required 0.5 μg of Fe per ml. Three percent, but not 0.1%, sea salts inhibited prodigiosin synthesis in a complex medium containing up to 10 μg of Fe per ml. NaCl was the inhibitory sea salt component. The inhibition was not specific for NaCl; equimolar concentrations of Na2SO4, KCl, and K2SO4 also inhibited prodigiosin synthesis. Experiments with strains 264 and Nima and with mutant WF which cannot synthesize 4-methoxy-2-2′-bipyrrole-5-carboxyaldehyde (MBC), the bipyrrole moiety of prodigiosin, and with mutant 9-3-3 which cannot synthesize the monopyrrole moiety 2-methyl-3-amylpyrrole (MAP) showed that both MBC synthesis and the reaction condensing MAP and MBC to form prodigiosin were relatively more sensitive to NaCl inhibition than the MAP-synthesizing step. The capacity of whole cells to condense MAP and MBC was present, but inactive, in cells grown in NaCl; removal of the NaCl from non-proliferating salt-grown cells restored the activity. Other evidence suggests the existence of a common precursor to the MAP- and MBC-synthesizing pathways.
Studies on prodigiosin and the bipyrrole precursor
Isolation and structure studies on prodigiosin, and on the C10H10O2N2 bipyrrole precursor are discussed. NMR data on a series of substituted pyrroles are listed showing characteristic chemical shifts of pyrrole-NH and pyrrole ring protons. The effect of electron-withdrawing and electron-releasing substituents on the absorption of α- and β-protons is shown.
STUDIES ON PIGMENTATION OF SERRATIA MARCESCENS I
The red pigment of Serratia marcescens, prodigiosin, has interested chemists because it has been reported to be the only naturally occurring tripyrrylmethene and as such its biosynthesis might be related to porphyrin biosynthesis (Hubbard and Rimington, 1950). Wrede and Hettche (1929) extracted the pigment from S. marcescens using a procedure involving sodium hydroxide treatment. By degrading the alkaliextracted pigment, Wrede and Rothhaas (1934) defined the structure of prodigiosin as a tripyrrylmethene, a single compound. Hubbard and Rimington (1950) extracted prodigiosin by means of acid and alkali and compared the spectral properties of the pigment to a synthetic tripyrrylmethene. Since the spectral properties of the two substances were similar, these authors concluded that the tripyrrylmethene structure of prodigiosin was probably correct, and implied that the pigment was a single substance. However, Weiss (1949) showed that prodigiosin extracted by a mild organic solvent, n-butyl alcohol, separated into several bands when chromatographed on columns of magnesium oxide or a mixture of calcium carbonate and celite. This fact suggested that Hubbard and Rimington (1950) might have dealt with a mixture of pigments which they assumed to be a single substance. Since Weiss (1949) indicated the mixed nature of extracted prodigiosin, we felt further study of mildly extracted prodigiosin was warranted. Unfortunately, n-butyl alcohol extraction did not give satisfactory results in our hands. As a consequence we have developed a different method for pigment extraction and for the sepa-