Fatty acid production from a highly CO₂ tolerant alga, Chlorocuccum littorale, in the presence of inorganic carbon and nitrate

Photoautotrophic fatty acid production of a highly CO₂-tolerant green alga Chlorococcum littorale was investigated in the presence of inorganic carbon and nitrate at 295 K and a light intensity of 170 μmol-photon m^-2 s^-1. CO₂ concentration in the bubbling gas was adjusted by mixing pure gas components of CO₂ and N₂ to avoid photorespiration and β-oxidation of fatty acids under O₂ atmosphere conditions. Fatty acid content was almost constant for the CO₂ concentrations ranging from 5% to 50% under nitrate-rich conditions corresponding to the logarithmic growth phase. After nitrate depletion, the content drastically increased with a decrease in CO₂ concentration. HCO₃^- / CO₂ ratio in the culture media was found to be a controlling factor for fatty acid production after the nitrate limitation phase. For a CO₂ concentration of 5%, the fatty acid content was ca. 34 wt.% at maximum, which is comparable with other land plant seed oils.