The synthesis of acetate by E. coli generally occurs as a result of the need of cells toregenerate cofactors used in glycolysis and to recycle coenzyme A.To initiate the tricarboxylic acid (TCA) cycle, pyruvate is convertedinto acetyl-CoA. Excess pyruvate or acetyl-CoA are directly con-verted to acetate. In aerobic conditions, acetate production occurswhen high concentrations of glucose inhibit respiration (Crabtreeeffect). Under these conditions, around 15% of the glucose is con-verted to acetate (Wolfe, 2005). In theory, if PPP is the majorpathway for glucose catabolism, both glycolysis and TCA cycle aredown-regulated, and thus acetate production is minimized (Usuiet al., 2012). Indeed, GALG20 produced very low amounts of acetateand did not accumulate any acetate at the end of the batch fermen-tation in the bioreactor or shake flask (Table 1).