Acetate metabolism in a pta mutant of Escherichia coli W3110: Importance of maintaining acetyl coenzyme a flux for growth and survival

In order to study the physiological role of acetate metabolism in Escherich ia coli, the growth characteristics of an E. coil W3100pta mutant defective in phosphotransacetylase, the first enzyme of the acetate pathway, were in vestigated. The pta mutant grown on glucose minimal medium excreted unusual by-products such as pyruvate, D-lactate, and L-glutamate instead of acetat e. In an analysis of the sequential consumption of amino acids by the pfa m utant growing in tryptone broth (TB), a brief lag between the consumption o f amino acids normally consumed was observed, but no such lag occurred for the wild-type strain. The pta mutant was found to grow slowly on glucose, T B, or pyruvate, but it grew normally on glycerol or succinate. The defectiv e growth and starvation survival of the pta mutant were restored by the int roduction of poly-beta-hydroxybutyrate (PHB) synthesis genes (phbCAB) from Alcaligenes eutrophus, indicating that the growth defect of the pta mutant was due to a perturbation of acetyl coenzyme A (CoA) flux. By the stoichiom etric analysis of the metabolic fluxes of the central metabolism, it was fo und that the amount of pyruvate generated from glucose transport by the pho sphoenolpyruvate-dependent phosphotransferase system (PTS) exceeded the req uired amount of precursor metabolites downstream of pyruvate for biomass sy nthesis. These results suggest that E. coli excretes acetate due to the pyr uvate flux from PTS and that any method which alleviates the oversupply of acetyl CoA would restore normal growth to the pta mutant.