Light acclimation and photoinhibition in three Spirulina platensis (cyanobacteria) isolates

Three isolates of Spirulina platensis (Norst) Geitler marked BP, P4P and Z19/2 were compared with respect to their response and acclimation capability to high photon flux densities (HPFD). Cultures exposed to HPFD (15003500/μmol photon m^-2 s^-1) exhibited a marked decrease in light- dependent O₂ evolution rate. P4P was more sensitive to HPFD than the two other isolates. All three isolates recovered from photoinhibition when placed under low PFD. The BP isolate was able to recover also in the dark but to a lower extent and at a lower rate, while no recovery was observed in the other two isolates under dark conditions. No recovery was observed when protein synthesis was inhibited using chloramphenicol. Cultures grown at 200 μmol photon m^-2 s^-1 differed from cultures grown at 120 μmol photon m 2 s-1 by their lower maximal photosynthetic rate (P(max)) and higher light saturation (I(k)) value, while being more resistant to HPFD stress. The ability of Spirulina isolates to acclimate and withstand HPFD may provide useful information for the selection of strains useful for outdoor mass cultivation.