| A stoichiometric model of metabolism was developed to describe the balance of metabolic reactions during steady-state growth of Escherichia coli. The model incorporates 163 reversible and 166 irreversible reactions and 283 metabolites for the biosynthesis of the macromolecular precursors, coenzymes, and prosthetic groups necessary for the synthesis of all cellular macromolecules. Correlations describing how the cellular composition changes with growth rate were used to calculate the drain of precursors for the synthesis of biomass macromolecules at a specific growth rate. Energy requirements for macromolecular polymerization and proofreading, transport of metabolites, and maintenance of transmembrane gradients were included in the model. The under-determined set of equations was solved using the Simplex algorithm, employing realistic objective functions and constraints; the drain of precursors, coenzymes, and prosthetic groups and the energy requirements for the synthesis of macromolecules served as the primary set of constraints. The model accurately predicted experimentally-determined metabolic fluxes for aerobic growth on acetate or acetate plus glucose as well as the genetic and metabolic regulation that must occur for growth under different conditions.; The amino acid composition of proteins and the fatty acid composition of the cell membranes were measured with exponentially growing cells in batch culture on glucose, succinate, glycerol, pyruvate and acetate, and in cells growing under continuous culture conditions on glucose at dilutions rates equivalent to the growth rates of the batch cultures. The sensitivity of the model to changes in fatty acid and amino acid composition was tested using data collected under batch and continuous growth conditions.; The model was used to study enhanced biological phosphorus removal (EBPR) in waste-water treatment, which involves metabolic cycling through several biopolymers (polyphosphate, polyhydroxyalkanoate (PHA) and glycogen). To understand how carbon, energy, and redox are channeled through the metabolic pathway during each cycle, the metabolic flux model was modified to include pathways necessary for the EBPR process. Data from a laboratory scale sequencing batch reactor that performs EBPR were used as inputs for the model. The model provided information on the pathways by which the energy-rich molecules ATP, NADH and NADPH were produced and consumed during the EBPR process. |
