We compared pyruvate accumulation in six strains of Escherichia coli and their corresponding ppc mutants. Each strain contained a mutation of a gene involved in the pathway to acetate synthesis. Strains with mutations in genes encoding the pyruvate dehydrogenase complex generally exhibited the greatest pyruvate accumulation of which CGSC6162 (an aceF mutant) and CGSC6162 Deltappc were studied in greater detail in controlled fermenters. Both CGSC6162 and CGSC6162 Deltappc accumulated greater than 35 g/l pyruvate in a medium supplemented with acetate. We observed pyruvate mass yields from glucose of 0.72 in CGSC6162, with volumetric productivities above 1.5 g l(-1) h(-1). For CGSC6162 Deltappc, we observed pyruvate yields of 0.78 and volumetric productivities above 1.2 g l(-1) h(-1). CGSC6162 consumed all initially supplied acetate, while CGSC6162 Deltappc first consumed and then generated acetate during the course of a 36 h fermentation. Acetate generation and pyruvate oxidase activity was pH- and temperature-dependent, with a pH of 7.0 and the lowest temperature studied (32degreesC) favoring the greatest pyruvate generation. Lactate was an unexpected by-product even though measured lactate dehydrogenase (LDH) activity was very low.