Hydrogen production and metabolic flux analysis of metabolically engineered Escherichia coli strains

摘要

Escherichia coli can produce H_2 from glucose via formate hydrogen lyase (FHL). In order to improve the H_2 production rate and yield, metabolically engineered E. coli strains, which included pathway alterations in their H_2 production and central carbon metabolism, were developed and characterized by batch experiments and metabolic flux analysis. Deletion of hycA, a negative regulator for FHL, resulted in twofold increase of FHL activity. Deletion of two uptake hydrogenases (1 (hya) and hydrogenase 2 (hyb)) increased H_2 production yield from 1.20 mol/mol glucose to 1.48 mol/mol glucose. Deletion of lactate dehydrogenase (IdhA) and fumarate reductase (frdAB) further improved the H_2 yield; 1.80 mol/mol glucose under high H_2 pressure or 2.11 mol/mol glucose under reduced H_2 pressure. Several batch experiments at varying concentrations of glucose (2.5-10 g/L) and yeast extract (0.3 or 3.0 g/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 IdhA and frdAB directed most of the carbons from glucose to the glycolytic pathway leading to H_2 production by FHL, not to the pentose phosphate pathway.