Decrease in respiration activity related to prodigiosin synthesis in Serratia marcescens

Associations between cellular levels of ATP and prodigiosin pigment throughout the growth cycle of Serratia marcescens

Serratia marcescens is a prolific producer of the red, membrane-associated pigment prodigiosin. Earlier work has established both a positive role for prodigiosin in ATP production during the population lag phase and a negative role during high-rate, low cell density growth. This study uses the growth rate and growth phase modulation afforded by chemostat culture to extend prodigiosin functional analysis to the high-density and stationary phases. Cellular levels of prodigiosin were positively associated with cellular levels of ATP during high-density growth, and artificial pigment induction during this phase increased cellular ATP levels. Following peak high-density ATP per cell, the early stationary phase enabled significant population growth, while prodigiosin levels remained high and ATP declined. During the late stationary phase, ATP per cell was positively associated with prodigiosin per cell, while both declined during continued growth. These results provide correlational evidence for the multiple effects of prodigiosin pigment on ATP production throughout the growth cycle. Earlier work and the data presented here enable the formulation of a working model for the oscillating relationships between cellular levels of ATP and prodigiosin during batch culture.

Production of prodigiosin pigment by Serratia marcescens is negatively associated with cellular ATP levels during high-rate, low-cell-density growth

Serratia marcescens is a facultatively anaerobic bacterium and the most recognized producer of the hydrophobic pigment prodigiosin. Previous work has shown that prodigiosin both increases ATP production during population lag phase and approximately doubles the stationary-phase cell yield. Here, we employed both batch and chemostat culture methods to investigate prodigiosin's role during high rate growth at low cell density as peak cellular ATP levels decline. Batch culture experiments utilizing artificial pigment induction showed an ATP reduction during low cell density growth. In addition, pigment induction during fixed growth rate chemostat culture revealed a negative correlation between cellular levels of prodigiosin and ATP (r = -0.95). Variable growth rate chemostat experiments showed an inverse relationship between ATP per cell and prodigiosin per cell during low-density growth but a direct relationship during high-density growth. Rate modeling of chemostat data quantified the pigment's effect on cellular levels of ATP for both population growth phases. Finally, prodigiosin production in a heterologous bacterium led to ATP decline. These data with intact cells complement the established in vitro proton import function of prodigiosin pigment and may indicate an energy-spilling function during high rate, low cell density growth.

Prodigiosin pigment of Serratia marcescens is associated with increased biomass production

Serratia marcescens is a gram-negative, facultatively-anaerobic bacterium and opportunistic pathogen which produces the red pigment prodigiosin. We employed both batch culture and chemostat growth methods to investigate prodigiosin function in the producing organism. Pigmentation correlated with an increased rate of ATP production during population lag phase. Results with a lacZ transcriptional fusion to the prodigiosin (pig) biosynthetic operon revealed that operon transcription is activated by low cellular levels of ATP at high cell density. Furthermore, these data enabled estimation of the ATP per cell minimum value at which the operon is induced. Pigmented cells were found to accumulate ATP more rapidly and to multiply more quickly than non-pigmented cells during the high density growth phase. Finally, results with both batch and chemostat culture revealed that pigmented cells grow to approximately twice the biomass yield as non-pigmented S. marcescens bacteria. Prodigiosin production may, therefore, provide a growth advantage at ambient temperatures.

Kinetic analysis of growth rate, ATP, and pigmentation suggests an energy-spilling function for the pigment prodigiosin of Serratia marcescens

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.

Separation of the prodigiosin-localizing crude vesicles which retain the activity of protease and nuclease in Serratia marcescens

Crude vesicles in which prodigiosin is localized were separated from pigmented Serratia marcescens. The bacteria were grown on peptone-glycerol agar plate, suspended in saline, and fractionated into cells, vesicles, and supernatant by differential centrifugation. Electron microscopic observations showed that the fractionation was conducted properly and the separated vesicles were lysed in distilled water. The vesicles suspended in saline retained 100 kilodalton protein of which amount is correlated with prodigiosin level, but the 100 kDa protein was found in the supernatant when the vesicles were lysed in distilled water. The vesicle fraction retained few colony-forming units and little detectable activity of NADH oxidase, but showed much higher activities of protease and nuclease than the cell fraction. The profiles of the activities of the protease and the nuclease in the fractions were different from each other, that is, the protease activity in the vesicle fraction was lower than that in the supernatant fraction, whereas the nuclease activity in the vesicle fraction was higher than that in the supernatant fraction, suggesting that the two extracellular enzymes were released from the pigmented bacteria by different mechanisms.

A protein associated with prodigiosin formation in Serratia marcescens

A protein associated to prodigiosin formation was found in Serratia marcescens. The protein was not found in nonpigmented strains and was correlated with the pigment level. The protein was about 100 kilodaltons (kDa) and was also found in nonpigmented bacteria of the pigmented strain grown in glucose medium, at high temperature, or under anaerobic condition. The 100 kDa protein was found not in the outer membrane and the periplasm, but in the inner membrane and/or the cytoplasm. The protein was also found singly or dominantly in pigment-protein complexes and pigment-localizing vesicles described in previous reports. These results suggest that the 100 kDa protein is associated with prodigiosin formation.