Kinetic Analysis of Growth Rate, ATP, and Pigmentation Suggests an Energy-Spilling Function for the Pigment Prodigiosin ofSerratia marcescens

Abstract

Serratia marcescens is a gram-negative environmental bacterium and opportunistic pathogen. S. marcescens expresses prodigiosin, a bright red and cell-associated pigment which has no known biological function for producing cells. We present here a kinetic model relating cell, ATP, and prodigiosin concentration changes for S. marcescens during cultivation in batch culture. Cells were grown in a variety of complex broth media at temperatures which either promoted or essentially prevented pigmentation. High growth rates were accompanied by large decreases in cellular prodigiosin concentration; low growth rates were associated with rapid pigmentation. Prodigiosin was induced most strongly during limited growth as the population transitioned to stationary phase, suggesting a negative effect of this pigment on biomass production. Mathematically, the combined rate of formation of biomass and bioenergy (as ATP) was shown to be equivalent to the rate of prodigiosin production. Studies with cyanide inhibition of both oxidative phosphorylation and pigment production indicated that rates of biomass and net ATP synthesis were actually higher in the presence of cyanide, further suggesting a negative regulatory role for prodigiosin in cell and energy production under aerobic growth conditions. Considered in the context of the literature, these results suggest that prodigiosin reduces ATP production by a process termed energy spilling. This process may protect the cell by limiting production of reactive oxygen compounds. Other possible functions for prodigiosin as a mediator of cell death at population stationary phase are discussed.Serratia marcescens is a ubiquitous environmental bacterium which has been isolated from soil, water, and insects (6). This organism has emerged as an important nosocomial pathogen associated with respiratory infections, urinary tract infections, sepsis, wound infections, and conjunctivitis among wearers of contact lenses (13,19,27). Environmental isolates of S. marcescens express the red, cell-associated pigment prodigiosin, but identification of most clinical isolates must rely on other biochemical markers because the majority are not pigmented (13,27).Prodigiosin has been traditionally known as a secondary metabolite: it has no clearly defined function in cellular metabolism (4). Several physiological processes in S. marcescens, including prodigiosin pigmentation and biofilm formation, are activated at high cell density by quorum-sensing mechanisms (26,28,30). Low phosphate concentrations and temperatures below 37°C favor strong pigmentation (29). At least 12 pigmentation (pig) genes (A through J; M and N), arranged as part of a larger pig operon, encode enzymes for prodigiosin biosynthesis. In addition, a suite of regulatory proteins provides fine genetic control at the level of transcription. Quorum-sensing regulation of pig operon expression is mediated by SmaR and SmaI (secondary metabolite activator) (24, 25). SmaR is a repressor with DNA binding activity (8); transcriptional repression is mi...

Serratia marcescens Cyclic AMP Receptor Protein Controls Transcription of EepR, a Novel Regulator of Antimicrobial Secondary Metabolites

“…Another potential benefit for secondary metabolite regulation to be tied to a central metabolic regulator, cAMP-CRP, is suggested by Haddix et al; prodigiosin was shown to have a role in energy spilling that may protect cells at high culture density (43). Furthermore, recent work supports that prodigiosin has a positive effect on cell yield (P. Haddix, personal communication).…”

SdhE Is a Conserved Protein Required for Flavinylation of Succinate Dehydrogenase in Bacteria

“…This study has demonstrated that sdhEygfX is a bicistronic operon, suggesting that these genes are functionally related, with both gene products affecting pig biosynthesis, directly or indirectly, at the level of transcription of the biosynthetic operon (pigA-O). This provides an additional link between carbon metabolism and the regulation of pig biosynthesis (11,45). Furthermore, deletion of sdhE affected multiple phenotypes, suggesting that multiple biological pathways might be affected.…”

Serratia marcescens Quinoprotein Glucose Dehydrogenase Activity Mediates Medium Acidification and Inhibition of Prodigiosin Production by Glucose

“…This membrane-associated red pigment is produced by some biotypes of Serratia marcescens (16), a Gram-negative bacterium found in the rhizosphere (22,36), salt and fresh water, insect and mammal guts, and hospitals (16). Evidence suggests that prodigiosin functions in bacterial dispersal (5), competition against other organisms (14,59), regulation of proton gradients, energy, and pH homeostasis (21,41,44), and determination of surface hydrophobicity (42,43). Recent work has shown that prodigiosin has immunosuppressive and antitumor properties that may be of high clinical value (reviewed by Perez-Tomas and Vinas [38]).…”