Metabolic Engineering

Abstract

In metabolic engineering, modern genetic techniques allied with contemporary bioreactor, biochemical, and mathematical methods enable systematic manipulation of the metabolic activities of living cells. One important class of metabolic engineering applications involves introduction into industrial microorganisms of heterologous activities that enhance the desired metabolic functions of the host. Expression of Vitreoscilla hemoglobin (VHb) in a variety of prokaryotic and eukaryotic hosts illustrates this approach. Escherichia coli engineered to express VHb exhibits a higher specific growth rate, increased proton pumping stoichiometry, and greater ATP production than VHb-free controls in oxygen-limited conditions. Intracellular expression of VHb also enhances lysine yield in fermentations of Cotynebacterium glutamicum and production of cephalosporin C by Acremonium chrysogemim. Another class of metabolic engineering applications manipulates the distribution of fluxes through metabolic pathways by altering regulation of expression and regulation of activities of enzymes in these pathways. These opportunities are illustrated by research aimed at redirecting carbon flow in the central catabolic pathways E. coli . Overproduction of glycogen synthesis enzymes in an E. coli mutant blocked for acetate synthesis substantially enhances growth yields and growth rates of this strain. Mathematical modeling calculations suggest even greater changes in internal fluxes can be achieved by manipulation of inhibition characteristics of pathway enzymes through protein engineering.