Fig 3. Light-intensity dependence of net oxygen production and consumption, as measured with a membrane-inlet mass spectrometer (MIMS), of wild type Synechocystis, its ΔOx and ΔFlv1-3 mutant derivatives and Chlorella.

Oxygen exchange was measured with MIMS as a function of increasing red light (659 nm) intensity in wild type Synechocystis (WT), the terminal-oxidase deletion mutant (ΔOx), the Mehler-like reaction deletion mutant (Δflv1-3) and Chlorella sorokiniana (Chlorella). Cells were grown in batch with 30 μmol photons m^-2 s^-1 blue/red fluorescent light (see Materials and Methods) in BG-11 medium complemented with 25 mM NaHCO₃. Prior to measurements, the cells were washed once and re-suspended in fresh BG-11 medium with 50 mM NaHCO₃. Cells were dark adapted for 30 minutes prior to the experiment. Experiments with Synechocystis and its mutant derivatives were conducted at 18°C and Chlorella at 30°C. ●, oxygen evolution measured as an increase in the concentration of ³²O₂; ◊, oxygen uptake measured as a decrease in the concentration of ³⁶O₂; Δ, net rate of photosynthesis (i.e. rate of net oxygen evolution + rate of oxygen uptake). Values shown are the average of duplicate measurements with standard deviation.