9-36: Hydrogen from Glucose: Complete Conversion via Synthetic Enzymatic Pathway

The potential of biohydrogen is tremendous for reducing the greenhouse gas emissions associated with hydrogen production by methane reforming.  By combining thermophilic phosphorylase, hydrogenase, and pentose phosphate pathway enzymes, glucan feedstock can be converted to biohydrogen at a higher yield than other biological hydrogen production methods such as fermentation.  Additional benefits of using synthetic pathway biotransformations such as this include engineering advantages such as higher reaction rates (compared to microbial production), lack of competing pathways, and minimization of biocatalyst cost per unit product.  Starch and cello-oligomer substrates have been used in this reaction in previous studies, but glucose monomers could not be utilized previously, due to the energetic requirement of coupling a hydrolysis event to phosphorylation.  This substrate limitation has been overcome in this study, using a combination of polymerized ortho-phosphate and the enzyme polyphosphate glucokinase.  As a result of this ability to use all glucan monomers in the substrate, complete conversion to hydrogen is demonstrated here for the first time.  In addition, the hydrogen production rate was increased in this study using a variety of strategies, resulting in an order of magnitude increase from the previous maximum of 4 mmol hydrogen per hour per liter of reactor volume.  These important results show the complete biological oxidation of glucose to hydrogen gas for the first time and the great promise of synthetic enzymatic pathways for future high-efficiency bio-based chemical production.