PROPOSED MECHANISM OF ACETATE ACCUMULATION IN 2 RECOMBINANT ESCHERICHIA-COLI STRAINS DURING HIGH-DENSITY FERMENTATION

The productivity of Escherichia coil as a producer of recombinant prot eins is affected by its metabolic properties, especially by acetate pr oduction. Two commercially used E. coil strains, BL21 (lambda DE3) and JM109, differ significantly in their acetate production during batch fermentation at high initial glucose concentrations. E. coil BL21 grow s to an optical density (OD, 600 nm) of 100 and produces no more than 2 g/L acetate, while E. coil JM109 grows to an OD (600 nm) of 80 and p roduces up to 14 g/L acetate. Even in fed-batch fermentation, when glu cose concentration is maintained between 0.5 and 1.0 g/L, JM109 accumu lates 4 times more acetate than BL21. To investigate the difference be tween the two strains, metabolites and enzymes involved in carbon util ization and acetate production were analyzed (isocitrate, ATP, phospho enolpyruvate, pyruvate, isocitrate lyase, and isocitrate dehydrogenase ). The results showed that during batch fermentation isocitrate lyase activity and isocitrate concentration were higher in BL21 than in JM10 9, while pyruvate concentration was higher in JM109. The activation of the glyoxylate shunt pathway at high glucose concentrations is sugges ted as a possible explanation for the lower acetate accumulation in E. coil BL21. Metabolic flux analysis of the batch cultures supports the activity of the glyoxylate shunt in E. coil BL21. (C) 1998 John Wiley & Sons, Inc.