Maintenance Cost and Biomass Recycling Determine Fitness of E. Coli During Starvation

To break down organismal fitness into molecular contributions, physiological costs and benefits of cellular components must be analyzed in all phases of the organism’s life cycle. For the model bacterium Escherichia coli, quantitative approaches to dissect its physiology are available for growth, but not for starvation conditions. We uncover that the exponential decay of viability during carbon starvation is a physiological steady state, in which death rate is quantitatively determined by the ratio of maintenance flux per viable cell to nutrient yield per perished cell. This fundamental relation permits quantitative insights into how environments and genetic elements affect bacterial survival, as exemplified by a study of the cost of a wasteful enzyme and the benefit of the stress response sigma factor rpoS. While the enzyme increases the maintenance flux and thereby the death rate, rpoS improves biomass recycling, decreasing the death rate. Our quantitative approach enables detailed analyses of how cellular components affect survival, and thus fitness, of non-growing cells.