Serhii Vakal

Introduction Cyanobacteria are oxygenic photosynthetic bacteria that use light energy to convert CO2 and H2O into organic molecules. They can utilize both CO2 and bicarbonate (HCO3−) as inorganic carbon (Ci) sources. When cyanobacteria evolved, the CO2 concentration of the atmosphere was high, but in the subsequent eons, the CO2 concentration decreased and a carbon-concentrating mechanism (CCM) including HCO3− transporters, specialized NDH-1 complexes and carboxysomes evolved (Long et al., 2016).

Fig. S1 Plasmid map of a BiFC construct to express Synechocystis flv1 and petF (Fed1) as fusion proteins with N- and C-terminal Venus fragments, respectively. Fig. S2 Characterisation of Fed mutants. Fig. S3 ‘Empty’ vector control experiments for BiFC. Fig. S4 O2 evolution, O2 uptake, and CO2 fixation in ΔFlv3 and ΔFNR mutant strains. Fig. S5 NAD(P)H fluorescence changes under 3% [CO2] and low irradiance. Fig. S6 Redox kinetics of PSI electron carriers in WT, ΔFlv3, ΔFNRL, and ΔFNRS cells. Fig.

Abstract Flavodiiron proteins (FDPs) catalyse light-dependent reduction of oxygen to water in photosynthetic organisms, creating an electron sink on the acceptor side of Photosystem I that protects the photosynthetic apparatus. However, the identity of the electron donor(s) and the molecular mechanisms regulating FDP activity have remained elusive.