Photoautotrophic and sustained H2 production by the pgr5 mutant of Chlamydomonas reinhardtii in simulated daily light conditions.

Green algae, such as Chlamydomonas reinhardtii , can produce H 2 efficiently using their hydrogenases, but these enzymes are O 2 -sensitive and compete with CO 2 -fixation for electrons. To overcome these limitations, we previously developed an anaerobic, carbon-limited protocol that keeps the Calvin-Benson cycle inactive, and the evolved O 2 is scavenged by an absorbent. The PROTON-GRADIENT REGULATION5 (PGR5)-deficient mutant performs better than the wild type in this system, as it produces at least 2.5-fold more H 2 and maintains its photosynthetic apparatus and hydrogenase activity even at the intensity of sunlight. However, as the pgr5 mutant is known to be sensitive to fluctuating light conditions, it is of paramount interest to determine how it reacts to changes in light intensity during H 2 production. Therefore, we developed an automated system to monitor H 2 production in thin layer cultures under simulated daily light conditions. We found that the pgr5 mutant outperformed the wild type strain by 100 % when light intensity was varied stepwise between 0 and 1000 μmol photons m−2s−1 during the day. Photosynthetic subunits, including PsbA, PSBO, CP47, PetB and PsaA, were fully preserved in the pgr5 mutant, and approximately 29 % of its original hydrogenase activity was sustained after 85 h of H 2 production in simulated daily light conditions. Hence, the pgr5 mutant is a promising candidate for H 2 production under the adverse light conditions that algae may encounter in bioindustry settings. [Display omitted] • An automated thin-cell layer H 2 production system for Chlamydomonas was developed. • The pgr5 mutant outperformed the wild type in simulated daily light conditions. • The photosynthetic and hydrogenase activities of the pgr5 were better preserved. • The pgr5 mutant shows promise for bioindustry settings with adverse conditions. [ABSTRACT FROM AUTHOR]