Tailoring cyanobacterial cell factories: Synechocystis sp. PCC 6803 and Synechococcus sp. PCC 7002 for photocatalytic hydrogen production.

In recent years, the challenges posed by global warming and the fossil fuel–driven energy crisis have highlighted the urgent necessity of developing renewable energy sources. Hydrogen, a clean and zero-emission energy carrier, has emerged as a promising substitute for fossil fuels and a potential solution to pressing global issues (Gong et al., 2023). However, traditional approaches - such as water electrolysis powered by renewable energy - remain constrained by low thermodynamic efDiciency and high infrastructure costs (Guerrero- Rodrı́guez et al., 2024). To address these challenges, the University of Parma is conducting the project “Enzimi artiDiciali per la produzione fotocatalitica di idrogeno in batteri fotosintetici” (ART-2-HYDROGEN) which aims to develop a sustainable system for hydrogen production through engineered photosynthetic cyanobacteria. Its main goal is to create a laboratory-scale prototype that can efDiciently produce molecular hydrogen relying solely on visible light as the energy source. This strategy provides a viable pathway toward scalable and environmentally friendly hydrogen production, avoiding the drawbacks of conventional electrochemical processes that often demand signiDicant amounts of electricity, frequently derived from non-renewable sources. To achieve this, a plasmid encoding an artiDicial outer membrane protein of cyanobacteria has been constructed for the genetic modiDication of Synechocystis sp. PCC 6803 and Synechococcus sp. PCC 7002. This protein forms part of artiDicial enzymes assembled on the cyanobacterial outer membrane using the SpyTag/SpyCatcher system, and is further functionalized with photochemical and redox catalytic centers. Preliminary results conDirm that engineered Synechocystis sp. PCC 6803 expressed the SpyCatcher-linked membrane protein. The photochemical and redox catalytic modules will then attach to the cyanobacterial cell wall via SpyTag, thereby optimizing their interaction with photosynthetic electron donors. This strategy has the potential to establish a novel class of biohybrid devices for sustainable energy applications by directly exploiting photosynthetic reducing power and surpassing the constraints of natural enzymatic systems.