Improvement of hydrogen production by metabolic engineering of Escherichia coli: Modification on both the PTS system and central carbon metabolism

Abstract

Lignocellulosic-based production of bio-hydrogen (H2) by Escherichia coli requires efficient consumption of pentoses and hexoses. However, carbon catabolite repression (CCR) causes sequential utilization of carbohydrates and in some cases null consumption of less preferred carbohydrates, such as xylose. In this work, we evaluated the effect of elimination of the phosphotransferase system (PTS), responsible for CCR in strain E. coli WDH (ΔhycA) on H2 production using mixtures of glucose-xylose as carbon source. Elimination of ptsG gene (glucose permease-enzyme IIB), allowed simultaneous consumption of glucose and xylose, and improved H2 production 1.2-times with respect to the parenteral strain. Whereas, elimination of ptsG gene in combination with deletion of ldhA (d-lactate dehydrogenase) and/or frdD (fumarate reductase) genes, improved H2 production 2.5-times with a H2 yield of 0.27 mol·C-mol−1, using mixtures of glucose/xylose or wheat straw hydrolysate. Interestingly, besides the improvement on H2 production, E. coli WDH-GFA (ΔhycA, ΔptsG, ΔfrdD, ΔldhA) strain also produced ethanol as the main carbon by-product. These results show that elimination of ptsG, in combination with a modified central carbon metabolism improves the production of H2.