Effects of nitrate and oxygen on photoautotrophic lipid production from Chlorococcum littorale

Effects of oxygen and nitrate on fatty acid/lipid production from a highly CO2-tolerant microalgal species Chlorococcum littorale were examined under photoautotrophic conditions of 295 K, a light intensity of 170 μmol-photon m−2 s−1, a bubbling CO2 concentration of 5% (v/v) and bubbling oxygen concentrations to be volumetrically adjusted by mixing oxygen gas with inert nitrogen gas at concentrations ranging from 0% to 95% (v/v). The results showed that maximum fatty acid content reached ca. 34 wt.% under oxygen-freely bubbling conditions and this value decreased to be ca. 20 wt.% when air-like oxygen concentration of 20% was chosen. This means that degree of the accumulation strongly depended on the level of bubbling oxygen concentrations, which can be a crucial factor after nitrogen depletion in the photoautotrophic culture system. TLC-FID/FPD analyses showed that triglycerides were found to be a dominant lipid class for this accumulation.