Biomass and Lipid Production in the Aerial Microalga Coccomyxa subellipsoidea KGU-D001 in the Liquid and Aerial Phases

Microalgal-biofilm culture has the advantages of less water requirement and higher lipid productivity. For efficient lipid production in an aerial phase condition, it is ideal to simultaneously induce microalgal biofilm growth and lipid accumulation. Biomass production and lipid accumulation in the aerial microalga Coccomyxa subellipsoidea KGU-D001 were investigated in the logarithmic growth phase. Initially, the alga was cultured in three different conditions: in liquid phase using Bold’s basal medium (BBM), and in the aerial phase in the presence or absence of BBM. In aerial phase conditions with nutrients (i.e., BBM), biomass production was prioritized over cell proliferation until approximately the 7th day of culture. In the liquid phase conditions, the ratio of total organic carbon to total nitrogen (C/N) in cells was almost constant during the culture period. However, in both aerial phase conditions, the C/N ratio increased during the culture period, more so in the absence of nutrients. The total fatty acid content also increased throughout the culture period. Then, algal cells were cultured for a 17-day culture; there would be a growth period of 10 days followed by a lipid accumulation period of 7 days. In such cultures in the presence of BBM, the biomass and lipid productivities (388 and 94.2 mg/m²/day) were both significantly higher in the aerial phase than in the liquid phase during the lipid production period. C. subellipsoidea can produce lipids even during growth if the CO₂ supply is efficient and the C/N ratio is high.