Hydrogen is considered a promising energy vector that can be produced from sustainable resources such as sunlight and water. In green algae, such as Chlamydomonas reinhardtii, photoproduction of hydrogen is catalyzed by the enzyme [FeFe]-hydrogenase (HydA). Although highly efficient, this process is transitory and thought to serve as a release valve for excess reducing power. Up to date, prolonged production of hydrogen was achieved by the deprivation of either nutrients or light, thus, hindering the full potential of photosynthetic hydrogen production. Previously we showed that the enzyme superoxide dismutase (SOD) can enhance HydA activity in vitro, specifically when tied together to a fusion protein. In this work, we explored the in vivo hydrogen production phenotype of HydA–SOD fusion. We found a sustained hydrogen production, which is dependent on linear electron flow, although other pathways feed it as well. In addition, other characteristics such as slower growth and oxygen production were also observed in Hyd–SOD-expressing algae. The Hyd–SOD fusion manages to outcompete the Calvin–Benson cycle, allowing sustained hydrogen production for up to 14 days in non-limiting conditions.

中文翻译：

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重新路由光合能量以在体内连续产生氢气

氢被认为是一种有前途的能源载体，可以从阳光和水等可持续资源中产生。在绿藻中，例如莱茵衣藻，光生氢是由 [FeFe]-氢化酶 (HydA) 催化的。尽管效率很高，但该过程是短暂的，并且被认为可以充当多余还原能力的释放阀。迄今为止，长时间的产氢是通过缺乏营养或光照来实现的，因此阻碍了光合作用产氢的全部潜力。之前我们证明超氧化物歧化酶 (SOD) 可以在体外增强 HydA 活性，特别是当与融合蛋白结合在一起时。在这项工作中，我们探索了 HydA-SOD 融合的体内产氢表型。我们发现持续的氢气产生依赖于线性电子流，尽管其他途径也为其提供能量。此外，在表达 Hyd-SOD 的藻类中还观察到了其他特征，例如生长较慢和产氧量较慢。Hyd-SOD 融合成功地超越了 Calvin-Benson 循环，允许在非限制条件下持续生产长达 14 天的氢气。