Sequential heterotrophy-dilution-photoinduction cultivation for efficient microalgal biomass and lipid production.

A novel cultivation strategy called "sequential heterotrophy-dilution-photoinduction" was developed for efficient algal biomass and lipid production. Three Chlorella species were first cultivated heterotrophically to achieve high cell density, then the broth was diluted to suitable concentration (2-5 g/L) and transferred to light environment for photoinduction. With this strategy, the Chlorella intracellular protein and chlorophyll increased rapidly to 50.87% and 32.97 mg/g by a 12-h illumination, which were close to the level of cells cultivated photoautotrophically. Moreover, the lipid contents were increased by 84.57%, 70.65% and 121.59% within 24-h photoinduction for C. vulgaris, C. pyrenoidosa and C. ellipsoidea, respectively. Maximum lipid content as 26.11% of biomass and maximum lipid productivity of 89.89 mg/L/d was both accomplished by C. pyrenoidosa. Further outdoor experiments showed consistent patterns. Therefore, the proposed strategy provided an effective approach for microalgal biomass production to meet the urgent need for both health food and biodiesel.