syltensis DSM 22749T was grown in SYMHC medium under an initial headspace gas atmosphere of 20% (v/v)

O2, C. halotolerans DSM 23344T in SYM medium containing 0.5% (v/v) Tween 80 under air atmosphere and P. rubra DSM 19751T in defined medium containing 5 mM DL-malate under an initial headspace gas atmosphere of 12% (v/v) O2. The amount of produced BChl a is symbolized by red bars for L. syltensis DSM 22749T, blue bars for C. halotolerans DSM 23344T and green bars for P. rubra DSM 19751T. Each experiment was performed in duplicate and the shown values represent means of two measurements. The ratio of photosynthetic pigments depends on the redox conditions The pigment stoichiometry in L. syltensis varied widely and depended on the incubation conditions. Under conditions of a reducing environment (excess substrate, low oxygen concentrations, darkness) the determined BChl a/spirilloxanthin ratios were below one, whereas under oxidative stress (substrate limitation, high oxygen concentrations, illumination with blue

light) the production of spirilloxanthin was inhibited and pigment ratios reached values above five (Figure 4). A similar interrelationship was previously found in C. litoralis[15], whereas the variation of pigment ratios in C. halotolerans and P. rubra did not correlate linearly with the environmental redox Rutecarpine conditions. Especially, in P. rubra the BChl a/spirilloxanthin ratios reached higher values under optimal conditions for expression of the photosynthetic apparatus as under suboptimal conditions, irrespective of the environmental redox conditions being too high or too low for optimal pigment expression. It is noteworthy, that in these strains

the observed variability of the pigment stoichiometry was independent of the total amount of produced photosynthetic pigments, which could indicate that the ratio and amount of produced photosynthetic pigments are controlled by two independent regulatory mechanisms. Figure 4 Pigment stoichiometry in cells grown under various incubation conditions. The determined photosynthetic pigment ratios are based on results obtained in the experiments shown in Figures 1B and 3. Bars illustrate pigment ratios obtained upon incubation with different amounts of a distinct carbon source and line graphs represent values determined upon growth under illumination with different light sources. Bars and graphs in red represent values of L. syltensis DSM 22749T, values of C. halotolerans DSM 23344T are given in blue colour and values of P. rubra DSM 19751T in green.

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