Decoupling Growth and Metabolism in Escherichia coli

Microbial chemical production involves an intrinsic tradeoff between biomass formation and product formation. Theoretically, the ideal resolution of this tradeoff is production during stationary phase, in which growth is limited but carbon is nevertheless abundant. However, microbes typically respond to such conditions by shutting down central metabolism. Decoupling growth and metabolism is therefore one of the central problems in host engineering for synthetic biology. In this study, we characterize the metabolism of the model bacterium Escherichia coli under a variety of stationary phase conditions and show significant variation in metabolic activity that strongly depends on the limiting nutrient. We find an unusual phenotype of high glucose uptake rates under conditions of magnesium limitation, suggesting a lack of intrinsic barriers to enhancing metabolic activity under other starvation conditions. Based on quantitative metabolomics, we suggest a role for phosphoenolpyruvate in regulating glucose uptake. We further focus on the condition of nitrogen limitation, where a key regulatory interaction is the inhibition of the glucose uptake enzyme PtsI by accumulation of alpha-ketoglutarate. We find that by manipulating the expression of PtsI, we can enhance metabolic rates under nitrogen starvation, and we investigate the effect of this enhancement on the productivity of several biofuel pathways. We will also discuss how high-throughput and single-cell based screening and selection approaches will be used to further enhance stationary phase productivity for renewable biochemical and biofuel production.