Engineering glucose metabolism of Escherichia coli under nitrogen starvation

A major aspect of microbial metabolic engineering is the development of chassis hosts that have favorable global metabolic phenotypes, and can be further engineered to produce a variety of compounds. In this work, we focus on the problem of decoupling growth and production in the model bacterium Escherichia coli , and in particular on the maintenance of active metabolism during nitrogen-limited stationary phase. We find that by overexpressing the enzyme PtsI, a component of the glucose uptake system that is inhibited by α-ketoglutarate during nitrogen limitation, we are able to achieve a fourfold increase in metabolic rates. Alternative systems were also tested: chimeric PtsI proteins hypothesized to be insensitive to α-ketoglutarate did not improve metabolic rates under the conditions tested, whereas systems based on the galactose permease GalP suffered from energy stress and extreme sensitivity to expression level. Overexpression of PtsI is likely to be a useful arrow in the metabolic engineer’s quiver as productivity of engineered pathways becomes limited by central metabolic rates during stationary phase production processes. Metabolic engineering: Boosting bacterial metabolism without growth Bacteria like Escherichia coli have become workhorses of metabolic engineering due to their potential for genetic manipulation and their fast metabolism. One major challenge in industrial metabolic engineering is the slowdown of metabolism that occurs when bacteria stop actively growing and dividing, even in the presence of available carbon. In this study, researchers from the Joint BioEnergy Institute observed that increasing the expression of a single protein involved in the E. coli sugar uptake system was sufficient to achieve a 4-fold increase in metabolic rates when growth was limited by nitrogen availability. This research is a prime example of the development of metabolic engineering “chassis strains”: bacterial strains with favorable metabolic and physiological phenotypes that can be used to improve production of a large number of biologically derived compounds.