A cell density-dependent metabolic switch in amino acid metabolism occurs in E. coli W3110 batch cultures at 1.15 g dry wt l(-1) (Han L, Doverskog M, Enfors S-O, Haggstrom L, 2002, J. Biotechnol. 92: 237-249). A two- to three-fold decrease of the concentration of most glycolytic and citric acid cycle metabolites, and an increase in acetyl-CoA concentration after the switch, indicates that the central metabolism also is affected. The specific acetate production rate decreases throughout the culture, except for a temporary increase at the switch point. The intracellular acetate concentration remains relatively constant during the culture.