Mixotrophic cultivation of Botryococcus braunii

Cultivation of Botryococcus braunii has been mainly reported in photoautotrophic mode which has some disadvantages such as low cell growth rate and low cell density. For high density and high productivity, this study attempts to cultivate B. braunii in mixotrophic mode. Effects of different organic carbon sources (including maltose, glucose, saccharose, lactose, glycerol and starch), glucose and KNO3 concentrations as well as inoculation amount on the growth of B. braunii were investigated in 250 mL shake flasks, and a fed-batch mixotrophic cultivation technique was developed in a 10 L enclosed automatic air-lift photobioreactor. unii grew faster in mixotrophic cultivation with all the six organic carbon sources than that in photoautotrophic mode, and glucose was the optimum. The optimal concentrations of glucose and KNO3 were 2.5 g L−1 and 0.4 g L−1 respectively. Within the inoculums of 46–200 g m−3, the lag phase of cell growth was very short, and cells grew fast into exponential phase after inoculation, the average cell growth rate of B. braunii increased with the increment of inoculation amount. With a 10 L air-lift photobioreactor, B. braunii was cultured by feeding glucose under mixotrophic condition for 19 days, and the cell density and hydrocarbon content in dry cell reached 4.55 g L−1 and 29.7%, respectively.