Hydrogen Production by CO₂ Deprived Photoautotrophic Chlamydomonas reinhardtii Cultures

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Vera I. Grechanik¹, Maxim A. Bol’shakov¹, and Anatoly A. Tsygankov^1,a*

¹Institute of Basic Biological Problems Russian Academy of Sciences, Pushchino Scientific Center for Biological Research, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia

^* To whom correspondence should be addressed.

Received July 6, 2022; Revised August 8, 2022; Accepted August 10, 2022

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Light-dependent hydrogen production by microalgae attracts attention of researchers because of the potential practical application. It is generally recognized that Calvin–Benson–Bassham cycle competes with hydrogen production process for electrons, and substrate (CO₂) limitation of the cycle can increase hydrogen production rate. Furthermore, photosystem II is not destroyed by CO₂ deficiency. We studied photoautotrophic cultures of Chlamydomonas reimhardtii under CO₂ deficiency. Under the flow of air with removed CO₂ the cultures reached stationary phase of growth and the photosystem II was downregulated due to overreduction of plastoquinone pool followed by degradation of the entire photosynthetic machinery. Under the Ar flow in the absence of CO₂ the cultures were brought to microaerobic conditions producing small amounts of hydrogen (5 ml H₂ day^–1 liter^–1 culture). Similar to the case of incubation under air atmosphere, prolonged incubation of cultures under microaerobic conditions resulted in down-regulation of photosystem II due to overreduction of plastoquinone pool with following degradation of whole photosynthetic machinery. Following removal of CO₂, transfer of cultures into dark anaerobic conditions (2.5 h), and illumination with low-intensity light resulted in the cultures producing H₂ with high initial rate. Total microalgal hydrogen production under these conditions was 56 ml H₂ liter^–1 culture. Thus, the CO₂-deprived photoautotrophic cultures produce hydrogen. Hydrogen production was limited by the toxic effect of oxygen on hydrogenase but not by the Calvin–Benson–Bassham cycle competition with hydrogen production process.

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KEY WORDS: microalgal hydrogen production, photoautotrophic cultures, Chlamydomonas reinhardtii, CO₂ deprivation

DOI: 10.1134/S0006297922100030

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