Inhibition of succinic acid production in metabolically engineered Escherichia Coli by neutralizing agent, organic acids, and osmolarity

Abstract

The economical viability of biochemical succinic acid production is a result of many processing parameters including final succinic acid concentration, recovery of succinate, and the volumetric productivity. Maintaining volumetric productivities >2.5 gL-1 h-1 is important ifproduction ofsuccinic acid from renewable resources should be competitive. In this work, the effects of organic acids, osmolarity, and neutralizing agent (NH4OH, KOH, NaOH, K2CO3, and Na 2CO3) on the fermentative succinic acid production by Escherichia coli AFP184 were investigated. The highest concentration of succinic acid, 77 g L-1, was obtained with Na2CO3. In general, irrespective ofthe base used, succinic acid productivity per viable cell was significantly reduced as the concentration of the produced acid increased. Increased osmolarity resulting from base addition during succinate production only marginally affected the productivity per viable cell. Addition ofthe osmoprotectant glycine betaine to cultures resulted in an increased aerobic growth rate and anaerobic glucose consumption rate, but decreased succinic acid yield. When using1 NH4OH productivity completely ceased at a succinic acid concentration of ∼40 g L-1. Volumetric productivities remained at 2.5 g L-1 h-1 for up to 10 h longer when K- or Na-bases where used instead of NH4OH. The decrease in cellular succinic acid productivity observed during the anaerobic phase was found to be due to increased organic acid concentrations rather than medium osmolarity. © 2009 American Institute of Chemical Engineers.