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Seol, Eunhee,Sekar, Balaji Sundara,Raj, Subramanian Mohan,Park, Sunghoon WILEY‐VCH Verlag 2016 Biotechnology Journal Vol.11 No.2
<P><B>Abstract</B></P><P>Hydrogen (H<SUB>2</SUB>) production from glucose by dark fermentation suffers from the low yield. As a solution to this problem, co‐production of H<SUB>2</SUB> and ethanol, both of which are good biofuels, has been suggested. To this end, using <I>Escherichia coli</I>, activation of pentose phosphate (PP) pathway, which can generate more NADPH than the Embden‐Meyhof‐Parnas (EMP) pathway, was attempted. Overexpression of two key enzymes in the branch nodes of the glycolytic pathway, Zwf and Gnd, significantly improved the co‐production of H<SUB>2</SUB> and ethanol with concomitant reduction of pyruvate secretion. Gene expression analysis and metabolic flux analysis (MFA) showed that, upon overexpression of Zwf and Gnd, glucose assimilation through the PP pathway, compared with that of the EMP or Entner‐Doudoroff (ED) pathway, was greatly enhanced. The maximum co‐production yields were 1.32 mol H<SUB>2</SUB> mol<SUP>−1</SUP> glucose and 1.38 mol ethanol mol<SUP>−1</SUP> glucose, respectively. It is noteworthy that the glycolysis and the amount of NAD(P)H formed under anaerobic conditions could be altered by modifying (the activity of) several key enzymes. Our strategy could be applied for the development of industrial strains for biological production of reduced chemicals and biofuels which suffers from lack of reduced co‐factors.</P>
Kim, Seohyoung,Seol, Eunhee,Oh, You-Kwan,Wang, G.Y.,Park, Sunghoon Elsevier 2009 International journal of hydrogen energy Vol.34 No.17
<P><B>Abstract</B></P><P><I>Escherichia coli</I> can produce H<SUB>2</SUB> from glucose via formate hydrogen lyase (FHL). In order to improve the H<SUB>2</SUB> production rate and yield, metabolically engineered <I>E. coli</I> strains, which included pathway alterations in their H<SUB>2</SUB> production and central carbon metabolism, were developed and characterized by batch experiments and metabolic flux analysis. Deletion of <I>hycA</I>, a negative regulator for FHL, resulted in twofold increase of FHL activity. Deletion of two uptake hydrogenases (1 (<I>hya</I>) and hydrogenase 2 (<I>hyb</I>)) increased H<SUB>2</SUB> production yield from 1.20mol/mol glucose to 1.48mol/mol glucose. Deletion of lactate dehydrogenase (<I>ldhA</I>) and fumarate reductase (<I>frdAB</I>) further improved the H<SUB>2</SUB> yield; 1.80mol/mol glucose under high H<SUB>2</SUB> pressure or 2.11mol/mol glucose under reduced H<SUB>2</SUB> pressure. Several batch experiments at varying concentrations of glucose (2.5–10g/L) and yeast extract (0.3 or 3.0g/L) were conducted for the strain containing all these genetic alternations, and their carbon and energy balances were analyzed. The metabolic flux analysis revealed that deletion of <I>ldhA</I> and <I>frdAB</I> directed most of the carbons from glucose to the glycolytic pathway leading to H<SUB>2</SUB> production by FHL, not to the pentose phosphate pathway.</P>