Synthetic biology for improved hydrogen production in Chlamydomonas reinhardtii

Hydrogen is a clean alternative to fossil fuels. It has applications for electricity generation and transportation and is used for the manufacturing of ammonia and steel. However, today, H(2) is almost exclusively produced from coal and natural gas. As such, methods to produce H(2) that do not use fossil fuels need to be developed and adopted. The biological manufacturing of H(2) may be one promising solution as this process is clean and renewable. Hydrogen is produced biologically via enzymes called hydrogenases. There are three classes of hydrogenases namely [FeFe], [NiFe] and [Fe] hydrogenases. The [FeFe] hydrogenase HydA1 from the model unicellular algae Chlamydomonas reinhardtii has been studied extensively and belongs to the A1 subclass of [FeFe] hydrogenases that have the highest turnover frequencies amongst hydrogenases (21,000 ± 12,000 H(2) s(−1) for CaHydA from Clostridium acetobutyliticum). Yet to date, limitations in C. reinhardtii H(2) production pathways have hampered commercial scale implementation, in part due to O(2) sensitivity of hydrogenases and competing metabolic pathways, resulting in low H(2) production efficiency. Here, we describe key processes in the biogenesis of HydA1 and H(2) production pathways in C. reinhardtii. We also summarize recent advancements of algal H(2) production using synthetic biology and describe valuable tools such as high‐throughput screening (HTS) assays to accelerate the process of engineering algae for commercial biological H(2) production.