Scaleable Hydrogen Production via Bioengineered Yeast Systems
Summary A new synthetic biology approach is proposed for producing hydrogen from bioengineered yeast strains. The invention applies aggressive engineering of metabolic pathways and reducing complexes to create a yeast microenvironment capable of producing hydrogen from glucose at theoretical maximum levels (approaching >50 kg hydrogen/ton of biomass) according to the glucose-hydrogen reaction:
C6H12O6 (glucose) + H2O Ã 6CO2 + 12H2.
In nature, while the overall economics of this reaction are favorable, especially if the glucose is derived from cellulose biomass or another crude source, most redox reactions in a cell use use NAD(P)H as a source of reducing equivalents â€“ the energetics of the reaction NAD(P)H + H+ Ã NAD(P)+ + H2 are not sufficiently favorable to proceed unless hydrogen is immediately withdrawn.
To address this problem, two approaches are being pursued. In the first approach, the laboratory is constructing artificial metabolic pathways, achieved by whole-scale export of heterologous metabolic pathways and large protein complexes, to generate stronger biological reducing agents. In the second approach, the Laboratory is constructing artificial organelles (microenvironments within cells) in which the NAD(P)H/NAD(P)+ ratio can be made arbitrarily high to drive the reaction to the right.
As a means of further enhancing development efforts, metabolic modeling approaches are being used to design the novel pathways in a rational manner, thereby avoiding deleterious synthetic pathways that prevent cell growth. Also, in addition to engineering new pathways in yeast, a complementary strategy includes engineering different organisms (both yeast and bacteria) that are each optimized for performing particular reactions. In this approach, an appropriate mixture of organisms will form a symbiotic system to produce hydrogen.
Applications Commercial development of engineered yeast systems should lead to a scaleable and efficient process for making H2 from biomass. Currently, various industries use hydrogen for semiconductor manufacture, food processing, metal processing, float glass, specialty chemicals and pharmaceuticals â€“ these markets account for an estimated market of over $2B.
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