초록
The green alga Haematococcus pluvialis, which accumulates astaxanthin at an optimal temperature of 20<SUP>o</SUP>C, was cultivated under temperatures of 20<SUP>o</SUP>C, 23.5<SUP>o</SUP>C, 27<SUP>o</SUP>C, and 30.5<SUP>o</SUP>C, in order to assess the effects on algal metabolism during the growth phase. The culture growth rate declined with above-optimal increases in temperature, and the final maximum cell concentration at 30.5<SUP>o</SUP>C reached only 35% of that attained at 20<SUP>o</SUP>C. On the contrary, the biomass productivity was increased under all the high-temperature conditions, probably reflecting the metabolism switch from cell duplication to energy accumulation that is typically observed in algal cultures subjected to environmental stress. Moreover, an increase in the light-harvesting capability of the alga was observed by means of the total pigment balance and the photosynthesis-intensity (PI) curve measured under the different cultivation conditions. Cultures kept at higher temperatures were able to better harvest and utilize the impinging light due to photo-acclimation. Finally, the differences in the astaxanthin metabolism were elucidated by subjecting the cultures to nitrogen starvation at 20<SUP>o</SUP>C and 27<SUP>o</SUP>C. In the culture at 27<SUP>o</SUP>C, a 1.4-fold increase in the astaxanthin productivity was observed when compared to that at 20<SUP>o</SUP>C, and the latter required almost two-fold more energy for the astaxanthin production compared with the 27<SUP>o</SUP>C culture.