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

Photosynthetic H2 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 O2 exposure to prolific, but O2-sensitive H2 producing enzymes-[FeFe] hydrogenases. CO2 supply and cell growth can also be limited so that most of the photosynthetic reduction capacity is directed toward H2 production. Yet, natural [FeFe] hydrogenases are still too O2 sensitive for technology implementation. We report the discovery of new variants and a new O2 tolerance mechanism that significantly reduce the sensitivity to O2 exposure without lowering H2 production rates or losing electrons to O2 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.