Mixotrophic culture of Chaetoceros sp. and its response to circadian rhythm

Chaetoceros sp. is widely used in aquaculture due to its high nutritional value. However, the low growth rate and poor light adaptability of Chaetoceros sp. limit their applications as aquatic food. In this study, the effects of different carbon and nitrogen sources on the growth of algal cells were studied. The highest algal cell density was 5.25*l06 cells/mL when glycerol concentration was 5.0 g/L in the mixotrophic culture. Correspondingly, the maximum algal cell density was 6.23*106 cells/mL when the concentration of nitrogen urea was 0.075 g/L. The lipid content was significantly increased to 156.5 mg/L under the mixotrophic culture. The characteristics of the response of Chaetoceros sp. to circadian rhythm were further studied. The dynamic analysis of cell volume showed that algal cell volume varied greatly under various culture conditions. Compared with the autotrophic model, the algal cell volume of the mixotrophic culture had a faster growth rate in the dark stage, with a peak at 8 h, which confirmed that there was sufficient energy for further cell growth in the dark stage under the mix-otrophic culture.