Redistribution of Metabolic Fluxes in the Central Aerobic Metabolic Pathway of E. coli Mutant Strains with Deletion of the ackA-pta and poxB Pathways for the Synthesis of Isoamyl

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• 作者：Cheryl R. Dittrich ; Ravishankar V. Vadali ; George N. Bennett ; and Ka-Yiu San
• 刊名：Biotechnology Progress
• 出版年：2005
• 出版时间：April 2005
• 年：2005
• 卷：21
• 期：2
• 页码：627 - 631
• 全文大小：234K
• 年卷期：v.21,no.2(April 2005)
• ISSN：1520-6033

文摘

Although the bacterium E. coli is chosen as the host in many bioprocesses, productsderived from the central aerobic metabolic pathway often compete with the acetate-producing pathways poxB and ackA-pta for glucose as the substrate. As such, asignificant portion of the glucose may be excreted as acetate, wasting substrate thatcould have otherwise been used for the desired product. The production of the esterisoamyl acetate from acetyl-CoA by ATF2, a yeast alcohol acetyl transferase, was usedas a model system to demonstrate the beneficial effects of reducing acetate production.All strains tested for ester production also overexpressed panK, a native E. coli genethat previous studies have shown to increase free intracellular CoA levels when fedwith pantothenic acid. A recombinant E. coli strain with a deletion in ackA-ptaproduces less acetate and more isoamyl acetate than the wild-type E. coli strain. Whenboth acetate-producing pathways were deleted, the acetate production was greatlyreduced. However, pyruvate began to accumulate, so that the overall ester productionremained largely unchanged. To produce more ester, a previously established strategyof increasing the flux from pyruvate to acetyl-CoA was adopted by overexpressing pyruvate dehydrogenase. The ester production was then 80% higher inthe poxB, ackA-pta strain (0.18 mM) than that found in the single ackA-pta mutant(0.10 mM), which also overexpressed PDH.