Heterotrophic production of Chlorella sp TISTR 8990biomass growth and composition under various production conditions

The green microalga Chlorella sp. TISTR 8990 was grown heterotrophically in the dark using various concentrations of a basal glucose medium with a carbon-to-nitrogen mass ratio of 29:1. The final biomass concentration and the rate of growth were highest in the fivefold concentrated basal glucose medium (25 g L-1 glucose, 2.5 g L-1 KNO3) in batch operations. Improving oxygen transfer in the culture by increasing the agitation rate and decreasing the culture volume in 500-mL shake flasks improved growth and glucose utilization. A maximum biomass concentration of nearly 12 g L-1 was obtained within 4 days at 300 rpm, 30 degrees C, with a glucose utilization of nearly 76% in batch culture. The total fatty acid (TFA) content of the biomass and the TFA productivity were 102 mg g(-1) and 305 mg L-1 day(-1), respectively. A repeated fed-batch culture with four cycles of feeding with the fivefold concentrated medium in a 3-L bioreactor was evaluated for biomass production. The total culture period was 11 days. A maximum biomass concentration of nearly 26 g L-1 was obtained with a TFA productivity of 223 mg L-1 day(-1). The final biomass contained (w/w) 13.5% lipids, 20.8% protein and 17.2% starch. Of the fatty acids produced, 52% (w/w) were saturated, 41% were monounsaturated and 7% were polyunsaturated (PUFA). A low content of PUFA in TFA feedstock is required for producing high quality biodiesel. (c) 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1589-1600, 2017