Photosynthetic hydrogen production: Novel protocols, promising engineering approaches and application of semi‐synthetic hydrogenases

Abstract

Photosynthetic production of molecular hydrogen (H2) by cyanobacteria and green algae is a potential source of renewable energy. These organisms are capable of water biophotolysis by taking advantage of photosynthetic apparatus that links water oxidation at Photosystem II and reduction of protons to H2 downstream of Photosystem I. Although the process has a theoretical potential to displace fossil fuels, photosynthetic H2 production in its current state is not yet efficient enough for industrial applications due to a number of physiological, biochemical, and engineering barriers. This article presents a short overview of the metabolic pathways and enzymes involved in H2 photoproduction in cyanobacteria and green algae and our present understanding of the mechanisms of this process. We also summarize recent advances in engineering photosynthetic cell factories capable of overcoming the major barriers to efficient and sustainable H2 production.

Generation of Synthetic Shuttle Vectors Enabling Modular Genetic Engineering of Cyanobacteria

“…Accordingly, cyanobacteria have a huge environmental impact as key players in global biogeochemical cycles . Due to their photosynthetic lifestyle, cyanobacteria have also drawn huge interest as promising biotechnological hosts, as they could be exploited for a sustainable and CO 2 -neutral production of fine chemicals or fuels. − …”

Light-Driven [FeFe] Hydrogenase Based H2 Production in E. coli: A Model Reaction for Exploring E. coli Based Semiartificial Photosynthetic Systems

“…[FeFe] hydrogenases can be found in many different microorganisms, including photosynthetic green algae. Photobiological H 2 production, albeit promising from a sustainability perspective, is limited by the low overall efficiency of natural photosynthesis. − This limitation has triggered the parallel development of biohybrid devices where enzymes are coupled with synthetic photosensitizers, achieving higher solar energy-to-product efficiencies. − However, the need to express and purify the enzymes in large quantities have made the scale-up of these systems challenging. Additionally, the high O 2 sensitivity of [FeFe] hydrogenases represents a major limitation. − Consequently, direct practical applications for this class of enzymes have remained limited in a solar fuel context .…”

Photochemistry and photoinhibition of the H-cluster of FeFe hydrogenases

“…Biological splitting of water into O 2 and H 2 can also be observed in photosynthetic microorganisms such as green algae and cyanobacteria 6 , but the combination of O 2 evolution and H 2 production is not a natural physiological pathway 7 , and it is severely limited by the oxygen sensitivity of the enzymes involved in H 2 production: hydrogenase or nitrogenase 6,[8][9][10][11] . Efforts have been made to genetically engineer the enzymes [12][13][14] or the strains 10 of these photosynthetic microorganisms, aiming for continuous, light-driven biological H 2 production [9][10][11][12][13][14][15] .…”