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R. Axayácatl González-García,E. Ines Garcia-Peña,Edgar Salgado-Manjarrez,Juan S. Aranda-Barradas 한국생물공학회 2013 Biotechnology and Bioprocess Engineering Vol.18 No.6
Increasing recombinant protein production yieldsfrom bacterial cultures remains an important challenge inbiotechnology. Acetate accumulation due to high dissolvedcarbon dioxide (pCO2) concentrations in the medium hasbeen identified as a factor that negatively affects suchyields. Under appropriate culture conditions, acetate couldbe re-assimilated by bacterial cells to maintain heterologousproteins production. In this work, we developed a simplifiedmetabolic network aiming to establish a reaction rate analysisfor a recombinant Escherichia coli when producing greenfluorescent protein (GFP) under controlled pCO2 concentrations. Because E. coli is able to consume both glucoseand acetate, the analysis was performed in two stages. Ourresults indicated that GFP synthesis is an independentprocess of cellular growth in some culture phases. Additionally,recombinant protein production is influenced bythe available carbon source and the amount of pCO2 in theculture medium. When growing on glucose, the increase inthe pCO2 concentration produced a down-regulation ofcentral carbon metabolism by directing the carbon fluxtoward acetate accumulation; as a result, cellular growthand the overall GFP yield decreased. However, the maximumspecific rate of GFP synthesis occurred with acetate as themain available carbon source, despite the low activity inthe other metabolic pathways. To maintain cellular functions,including GFP synthesis, carbon flux was re-distributedtoward the tricarboxylic acid cycle and the pentose phosphatepathway to produce ATP and NADH. The thermodynamicanalysis allowed demonstrating the feasibility of the simplifiednetwork for describing the metabolic state of a recombinantsystem.