The photosynthetic defect in ccs4Δccs5 is partially rescued by exogenous thiols. a) Ten-fold dilution series of WT (CC-4533), Δccs5 (CC-5922), ccs4 (CC-5925), ccs4Δccs5 (CC-5927), and ΔpetA (CC-5935) were plated on acetate and minimal medium with or without MESNA (2-mercaptoethane sulfonate sodium). Cells grown phototrophically (CO₂) were incubated at 25°C for 20 days with 30–50 µmol/m²/s of light. Cells grown mixotrophically (acetate + CO₂) were incubated at 25°C for 14 days with 0.3 µmol/m²/s of light. The horizontal lines indicate cropping from the same plate of serial dilution. b) Fluorescence transients were measured on cells grown on solid acetate-containing media for 5 days (with 0.3 µmol/m²/s of light) with or without MESNA. Strains are as in (a) except that the ccs4Δccs5 strain is CC-4518.