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The energy of cyanobacterial hydrogen (H 2) produced via bio-photolysis is being investigated as a potential solution to early-century environmental challenges. The main limiting factors of cyanobacterial H 2 photoproduction are the availability of electrons for [NiFe]-hydrogenase (H 2 ase) and the suppression of bidirectional H 2 ase activity induced by O 2 acquired from water molecules splitting in photosystem II. The current study investigated how photosynthetic inhibitors (PIs) affected H 2 production in non-N 2 -fixing cyanobacteria. Study findings revealed a rather high H 2 yield in Synechocystis sp. PSU 1262, as well as a beneficial (14.2-fold) influence of 500 μmol KCN on the H 2 production by the aforesaid strain. A 12/6-h light/dark cycle increased H 2 production by 80.3% in cells supplemented with 500 μmol KCN. Under the optimised conditions, the photobiological H 2 production of Synechocystis sp. PSU 1262 increased from 49.6 to 1552 nmol H 2 mg−1 Chl a h−1. PIs suppressed chlorophyll a concentration under illumination, lowering the O 2 levels, which enhanced bidirectional H 2 ase activity in Synechocystis sp. PSU 1262 cells. Applying varied light modes, preceded by the incorporation of PIs at optimal concentrations in H 2 production by research cyanobacterial strains, improved the H 2 yield and contributed significantly to the research originality. [Display omitted] • Six species of cyanobacteria from different ecosystems were isolated and identified. • The H 2 -producing activity of the strains was studied in the dark and in the light. • The effect of four inhibitors of photosynthesis on H 2 production was studied. • The effect of light and dark modes was evaluated on H 2 production by cyanobacteria. [ABSTRACT FROM AUTHOR]

Over the last five decades, solar-based hydrogen (H 2) production has been intensively studied. Specifically, the study of biophotolysis by cyanobacteria has received great attention to produce H 2 , and promising research approaches have been established. To date, numerous photobioreactors (PBRs) have been built to collect cyanobacterial biomass and generate bioenergy. Additionally, different PBR parameters were adjusted to increase the product yield. PBR development holds great potential not only for cell biomass but also for biological H 2 production. This review aimed to examine the mechanisms involved in H 2 production by cyanobacteria, explore the factors influencing the process, and describe five distinct PBRs known for their high H 2 production. This article examines the pros and cons of the most efficient PBRs for H 2 production and offers insights into strategies for increasing their productivity. [Display omitted] • Photosynthetic H 2 production processes was discussed. • Physiochemical factors affecting H 2 production were explained. • Five PBRs for H 2 production were described. • Advantages/disadvantages of PBRs used for H 2 production were described. [ABSTRACT FROM AUTHOR]