Effects of culture temperature shift and light-dark time cycle on the cellular sugar accumulation of Chlorella pyrenoidosa

We investigated the effect of culture temperature on the maximum specific growth rate and the cellular sugar accumulation, and the effect of a temperature shift on the sugar accumulation of Chlorella pyrenoidosa cells in a batch culture system. Increase in temperature below 30?°C appeared to correlate with increase in the maximum specific growth rate, on the contrary the cellular sugar content showed a reverse tendency against temperature. We attempted to utilize this tendency for improving sugar productivity in Chlorella. First, we cultured Chlorella at 28?°C during the logarithmic growth phase to obtain a high specific growth rate. The culture temperature was then shifted from 28?°C to 22?°C at the late logarithmic growth phase in order to reduce the specific growth rate and enhance the cellular sugar accumulation. As a result, we obtained a 15% increase in sugar production over that obtained by cultivation at 28?°C throughout the 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 concentration. Among the examined light-dark time cycles, maximum sugar productivity was obtained in the case of 12?h light and 12?h dark period.