SHORT-TERM PHOTOINHIBITION INDUCES LONG-TERM HYDROGEN PHOTOPRODUCTION IN A PHOTOTROPHIC CULTURE OF Chlorella sorokiniana ON COMPLETE MEDIUM

This work demonstrates, for the first time, the capacity of Chlorella sorokiniana immobilized in alginate to produce hydrogen (H) over an extended period when cultivated under strictly photoautotropic conditions on complete mineral medium. In order to reduce photosynthetic activity, immobilized cells were subjected to a 30-minute pre-incubation period at a high light intensity of 1000 μmol photons m s. The ability to produce H was evaluated under illumination of 40 μmol/(m s). The culture not bubbled with argon produced H for 9 days; the total gas yield was 0.1 mol H/m. In an argon atmosphere, the release of H continued for 51 days, resulting in a total yield of 0.55 mol H/m. The immobilized culture was capable of H production at 16% O in the gas phase, which may be due to the effects of photoinhibition and activation of oxygen uptake pathways in mitochondria and chloroplast. Analysis of the functioning of the electron-transport chain in microalgae cells revealed a decrease in the rate of electron transport, an increase in the size of the PSII antenna and the development of non-photochemical quenching processes, while the activity of PSII remained moderately high (Fv/Fm = 0.4–0.6). Inhibitor analysis using 10 M DCMU demonstrated that the contribution of PSII to the hydrogenase reaction increased from 30% on the first day of the experiment to 50% by the fourth day. The addition of 10 M DBMIB led to a 90% reduction in the rate of H formation on both day 1 and day 4.