EFFECTS OF CULTURE TEMPERATURE SHIFT AND LIGHT-DARK TIME CYCLE ON THECELLULAR SUGAR ACCUMULATION OF CHLORELLA-PYRENOIDOSA

We investigated the effect of culture temperature on the maximum speci fic growth rate and the cellular sugar accumulation, and the effect of a temperature shift on the sugar accumulation of Chlorella pyrenoidos a cells in a batch culture system. Increase in temperature below 30 de grees C appeared to correlate with increase in the maximum specific gr owth rate, on the contrary the cellular sugar content showed a reverse tendency against temperature. We attempted to utilize this tendency f or improving sugar productivity in Chlorella. First, we cultured Chlor ella at 28 degrees C during the logarithmic growth phase to obtain a h igh specific growth rate. The culture temperature was then shifted fro m 28 degrees C to 22 degrees C at the late logarithmic growth phase in order to reduce the specific growth rate and enhance the cellular sug ar accumulation. As a result, we obtained a 15% increase in sugar prod uction over that obtained by cultivation at 28 degrees C throughout th e culture. We also investigated the effect of light-dark time cycle on the sugar productivity and found that this operating variable did not affect the cellular sugar content but influenced the final cell conce ntration. Among the examined light-dark time cycles, maximum sugar pro ductivity was obtained in the case of 12 h light and 12 h dark period.