System analysis and improved [FeFe] hydrogenase O2 tolerance suggest feasibility for photosynthetic H2 production

Photosynthetic H-2 production has been a compelling but elusive objective. Here we describe how coordinated bioreactor, metabolic pathway, and protein engineering now suggest feasibility for the sustainable, solar-powered production of a storable fuel to complement our expanding photovoltaic and wind based capacities. The need to contain and harvest the gaseous products provides decisive solar bioreactor design advantages by limiting O-2 exposure to prolific, but O-2-sensitive H-2 producing enzymes-[FeFe] hydrogenases. CO2 supply and cell growth can also be limited so that most of the photosynthetic reduction capacity is directed toward H-2 production. Yet, natural [FeFe] hydrogenases are still too O-2 sensitive for technology implementation. We report the discovery of new variants and a new O-2 tolerance mechanism that significantly reduce the sensitivity to O-2 exposure without lowering H-2 production rates or losing electrons to O-2 reduction. Testing the improved hydrogenases with a biologically derived, light-dependent electron source provides evidence that this game changing technology has the potential for sustainable large-scale fuel production.