Enhancement of lipid productivity in Chlorella pyrenoidosa by collecting cells at the maximum cell number in a two-stage culture strategy

Two-stage culture strategies have been widely applied to improve biomass growth and lipid accumulation in microalgae. Most studies on two-stage culture strategies collect microalgal biomass at the maximum biomass concentration in the first stage and then transfer this biomass into the second stage for subsequent culture. However, there is no scientific conclusion regarding the appropriate time for microalgal biomass collection in the first stage. In this study, the biomass of Chlorella pyrenoidosa was collected at the maximum cell number and maximum biomass concentration in the first stage, and then transferred to the second stage for lipid accumulation. The results show that superior lipid productivity was achieved when using algal cells collected at the maximum cell number than those collected at the maximum biomass concentration. This was due to the strong cell proliferation ability of C. pyrenoidosa at the maximum cell number in the first stage. Moreover, the culture time of the first stage was shortened from 96 h to 48 h for autotrophic culture and 96 h to 60 h for heterotrophic culture. The results presented herein are of great significance for optimizing the current two-stage culture strategies.