Effects of Implementing Psi-light on Hydrogen Production via Biophotolysis in Chlamydomonas reinhardtii Mutant Strains

A new strategy in hydrogen production via biophotolysis developed previously was implemented in mutant strains ofChlamydomonas reinhardtii. Implementing PSI-light (photosystem I 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 (photosystem II) under radiation. 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 hours in a chlorophyll b deficient mutant (Cbn 1-48) and a very high light tolerant mutant (VHL^R-S4) yielding H₂ at 220.33 and 175.64 µL·mg^-1 Chlorophyll (= H₂ at 4243.05 and 8731.39 µL·mg^-1 dry cell weight), respectively. In addition, by iterating light and dark every 1.5 hours with PSI-light, hydrogen production was successfully extended to 27 hours yielding H₂ at 365.61 µL·mg^-1 Chlorophyll (= H₂ at 8812.12 µL·mg^-1 dry cell weight) in cbn 1-48. Further, greater energy conversion efficiency from radiation energy to formation of hydrogen molecules was achieved with the combination of PSI-light and some mutant strains compared to alternate methods of biophotolysis.