Enhanced H2 photoproduction in sodium sulfite-treated Chlamydomonas reinhardtii by optimizing wavelength of pulsed light

Photosynthetic hydrogen induced by Chlamydomonas reinhardtii presents a promising pathway for producing clean and renewable biofuel. Whereas, this process is transient owing to the repression of [FeFe]-hydrogenase by the oxygen co -evolved in photosystem II. Pulsed light is employed to prevent O-2 accumulation and the activation of Calvin-Benson-Bassham cycle for sustainable H-2 . While light quality significantly influences photosynthesis, the optimal wavelength for pulsed light -induced H-2 production remains not fully elucidated. Continuous irradiation at 660 - 670 nm performs poorly in H-2 production due to the activation of PSII, which is responsible for water oxidation. However, in this study, O(2 )was removed using a combination of pulsed light and sulfite treatment. Among six light regimes with different wavelengths, pulsed light peaking at 660 nm resulted in the highest photo -H-2 evolution, reaching approximately 180 mL L -1 within three days. This value was 1.4 times higher than that achieved under conventionally white pulsed light. Exposure to 660 nm red pulsed light not only sustained high activity of PSII and hydrogenase but also reduced the gene expression levels of ribulose-1,5bisphosphate carboxylase/oxygenase and ferredoxin-NADP + reductase, which was supposed to attenuate the competing effects of CBB cycle. This finding optimizes an efficient light source for pulsed light -induced H-2 production and demonstrates a great potential for refining pulsed light parameters to improve H-2 production in algae in the future.