the volumetric productivity of the two strains in batch mode-operated bioreactors was similar (∼90 mg/L). These results couldbe associated with acetate consumption during batch fermen-tation by MG1655endArecA. Although acetate accumulationwas observed when using MG1655endArecA in shake flasks(∼3.1 mg/L at harvest), the same strain eventually consumed allthe acetate produced during batch fermentation (Table 1). Inter-estingly, GALG20 produced similar amounts of pDNA in both shakeflask and batch-mode bioreactor; however, DH5 produced morepDNA in the bioreactor than in a shake flask (Table 1).Acetate consumption usually occurs when the carbon sourceis depleted and cells start to assimilate acetate. The synthesis ofacetate 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).