Fig 1.
Variable chl a fluorescence as measured with a pulse-amplitude modulated (PAM) fluorescence in wild type Synechocystis, three of its mutant derivatives, and the green alga Chlorella.
Batch cultures of wild type Synechocystis, the ndhB deletion mutant M55, the triple terminal oxidase deletion mutant ΔOx, the phycobilisome-free PAL mutant and the green alga Chlorella were grown in blue/red fluorescent light (see Materials and Methods). Cells for chl a fluorescence recordings were harvested in the linear phase of growth and incubated in a flat-panel flask. Prior to the experiment the cultures were dark adapted for 30 minutes and exposed to 2 minute illumination periods with red (659 nm) light with increasing light intensity ranging from 30–400 μmol photons m-2 s-1, as indicated by the shaded bar. Light intensities used were 30, 60 and 100 μmol photons m-2 s-1 followed by 50 μmol photons m-2 s-1 increases at each step until 400 μmol photons m-2 s-1. The asterisk indicates the growth light intensity of the pre-culture. In the middle of each period (i.e. after 1 min) the cells were subjected to a strong ‘white’ light pulse (2000 μmol photons m-2 s-1). Following the actinic light series, the cells were left in darkness for 5 minutes. The + marks when DCMU was added at a final concentration of 20 μM together with strong red light at an intensity of 400 μmol photons m-2 s-1.
Table 1.
The respiratory chain and the phycobilisomes affect chl a parameters.
Fig 2.
Light-intensity dependence of the photochemical and non-photochemical quenching in wild type Synechocystis, its mutant derivatives M55 and ΔOx, and the green alga Chlorella.
Light-intensity dependent levels of photochemical (♦, qP) and non-photochemical quenching (●, qN). Values were derived from the data described and depicted in Fig 1. QP was calculated as (FM'-F)/(FM'-F0') and qN as 1-((FM'-F0')/(FM-F0)) with: F0, lowest level of fluorescence after dark adaptation; F0' lowest level of fluorescence after light incubation; F, steady-state fluorescence in the presence of actinic light; FM, fluorescence upon a strong light pulse on dark adapted cells or after addition of DCMU (ΔOx mutant only). FM', fluorescence upon a saturation pulse in the presence of actinic light. Data are the average from duplicate measurements, standard deviation was between 1 and 5%.
Table 2.
Comparison of the efficiency of photosynthesis in a pro- and a eukaryotic oxyphototroph in terms of moles of photons required for biomass production and electron pair generation at moderate light intensities.
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.
Fig 4.
Schematic overview of the redox state of the components of the photosynthetic electron transport chain.
Schematic overview of the redox state of the photosynthetic electron chain in dark (left) and light (right) for Synechocystis (top) and Chlorella (bottom). The grey color indicates the level of reduction (the darker the more reduced) of the different intermediates or, in case of P680, P700 and NADP(H), the predominant species.