Effects of implementing PSI-light on hydrogen production via biophotolysis in Chlamydomonas reinhardtii mutant strains

• Implementing PSI-light improved H2 production in Chlamydomonas reinhardtii.
• Combination of PSI-light application and use of mutants increased H2 production.
• Introduction of light iteration technique to increase H2 production longevity.
• Improved energy conversion efficiency was observed under PSI-light application.

A new strategy in hydrogen production via biophotolysis developed previously was implemented in mutant strains of Chlamydomonas reinhardtii. Implementing PSI-light successfully demonstrated improved hydrogen production in the wild type strain of C. reinhardtii in a previous study, however, the results also showed rapid attenuation of hydrogen production even under PSI-light due to inhibited hydrogenase activity caused by oxygen, which was simultaneously produced through the water splitting reactions of PSII under light. In order to further decrease oxygen generation under PSI-light during the hydrogen production phase, use of some mutant strains of C. reinhardtii, that are known to show limited oxygen generation, were investigated.Continuous supply of PSI-light after a short anaerobic adaptation under dark conditions achieved significantly prolonged hydrogen production up to ≈ 18 h in a chlorophyll b deficient mutant (cbn 1–48) and a very high light tolerant mutant (VHLR-S4) yielding chlorophyll content based H2 production of 220 and 176 dm3 kg−1 (equivalent to dry cell weight based H2 production of 4.24 and 8.73 dm3 kg−1), respectively. In addition, by iterating light and dark every 1.5 h with PSI-light, hydrogen production was successfully extended to 27 h yielding chlorophyll content based H2 production of 366 dm3 kg−1 (equivalent to dry cell weight based H2 production of 8.81 dm3 kg−1) in cbn 1-48. Further, greater energy conversion efficiency from light to the formation of hydrogen molecules was achieved with the combination of PSI-light and some mutant strains compared to alternate methods of biophotolysis.