Effects of environmental stresses on the pigment compositions and physiological properties of Antarctic microalga Pyramimonas gelidicola

Abstract

Antarctic flagellate Pyramimonas gelidicola (KOPRI AnM0046) is a dominant green algal species found in Southern Ocean and ice&#8211

covered lakes such as Ace Lake. This microalga, one of the most important primary producers in those cold ecosystems, undergoes freeze-thaw cycles, extreme fluctuations in irradiance, large variations in nutrient and salinity. To understand how this species acclimates to these environmental changes, we investigated changes of pigment compositions and light utilization efficiency after cold shock treatment and light stress. Light stress was given by shifting P. gelidicola cultured at 4℃, 90 &micro

mol m-2s-1 to 15 &micro

mol m-2s-1 at the same temperature. Cold shock treatment was done by transferring P. gelidicola cultured in f/2 media at 8℃, 15 &micro

mol m-2s-1 to 4℃ and -1℃ at the same light intensity. After these treatments, cells were harvested and analyzed with HPLC and Fluorescence Induction and Relaxation (FIRe). The FIRe is a technique to measure maximum quantum efficiency of photochemistry. Shifting to low irradiance resulted in 64% growth rate reduction while it led to 10% increase in the maximum quantum yield of photosynthesis (Fv/Fm). Pigment analysis using HPLC also validated the improved quantum yield, showing the augmented accessory light-harvesting pigment. The ratio of zeaxanthin to violaxanthin was 2.641:0.517 (High irradiance: Low irradiance). On the other hand, the effect of abrupt cold stress on the pigment compositions was insignificant. However the maximum quantum yield of photosynthesis was higher in the lower temperature than higher temperature, suggesting that photosynthesis of this microalga is optimized in the cold temperature. In conclusion, these data show that photosynthesis of P. gelidicola is optimized at lower temperature and that like mesophilic microalgae pigment composition of P. gelidicola at different light intensity was changed to adjust photon utilization efficiencies. Since P. gelid