Abstract
In order to establish a culture method for a long-term preservation of microalgae, we investigated physiological responses of a model alga, Chlamydomonas reinhardtii, to low temperatures. When the cells pre-cultured at 25oC were exposed to temperatures below 25oC, growth rate of the cells was decreased with decreasing temperatures but they still grew at over 8oC. After cultured at 4oC for 7 days, the cells did not grow, but viability was more than 90%. When a cultural period at 4oC was extended to 80 days, viability was decreased to about 3%. Furthermore, viability was decreased to about 50% after 2 days and to below 1% after 7 days at -2oC. These results suggest that growth of C. reinhardtii cells are prevented, keeping physiological function to grow, at low temperatures over 4oC, and that the cells at non-freezing temperatures below 0oC are rapidly and severely injured and become no longer viable.
