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Co-production of hydrogen and ethanol by pfkA-deficient Escherichia coli with activated pentose-phosphate pathway: reduction of pyruvate accumulation
- Sundara Sekar, Balaji, Seol, Eunhee, Mohan Raj, Subramanian, Park, Sunghoon
- Biotechnology for biofuels 2016 v.9 no.1 pp. 95
- Escherichia coli, NAD (coenzyme), acetates, acetyl coenzyme A, biofuels, enzymes, ethanol, glucose, glycolysis, hydrogen, hydrogen production, prediction, pyruvic acid, reverse transcriptase polymerase chain reaction
- BACKGROUND: Fermentative hydrogen (H₂) production suffers from low carbon-to-H₂ yield, to which problem, co-production of ethanol and H₂ has been proposed as a solution. For improved co-production of H₂ and ethanol, we developed Escherichia coli BW25113 ΔhycA ΔhyaAB ΔhybBC ΔldhA ΔfrdAB Δpta-ackA ΔpfkA (SH8*) and overexpressed Zwf and Gnd, the key enzymes in the pentose-phosphate (PP) pathway (SH8*_ZG). However, the amount of accumulated pyruvate, which was significant (typically 0.20 mol mol⁻¹ glucose), reduced the co-production yield. RESULTS: In this study, as a means of reducing pyruvate accumulation and improving co-production of H₂ and ethanol, we developed and studied E. coli SH9*_ZG with functional acetate production pathway for conversion of acetyl-CoA to acetate (pta-ackA ⁺). Our results indicated that the presence of the acetate pathway completely eliminated pyruvate accumulation and substantially improved the co-production of H₂ and ethanol, enabling yields of 1.88 and 1.40 mol, respectively, from 1 mol glucose. These yields, significantly, are close to the theoretical maximums of 1.67 mol H₂ and 1.67 mol ethanol. To better understand the glycolytic flux distribution, glycolytic flux prediction and RT-PCR analyses were performed. CONCLUSION: The presence of the acetate pathway along with activation of the PP pathway eliminated pyruvate accumulation, thereby significantly improving co-production of H₂ and ethanol. Our strategy is applicable to anaerobic production of biofuels and biochemicals, both of which processes demand high NAD(P)H.