Masaki Ota

Effects of light intensity and temperature on photoautotrophic growth of a green microalga, Chlorococcum littorale

A highly CO2-tolerant green alga, Chlorococcum littorale, was investigated at temperatures ranging from 8 to 28 °C, light intensities from 30 to 170 μmol m−2 s−1, a constant CO2 concentration of 5% (v/v) and atmospheric pressure. The experimental results showed that a specific growth rate μ, defined in terms of cell growth rate under a logarithmic growth phase, increased with temperature up to the maximum value (ca. 22 °C), while the μ decreased at higher temperatures. These promotion and inhibition of the cell growth rate were expressed by both a multiple linear regression and a mathematical model taking account of the Arrhenius activation/deactivation energies. Light intensity affected on the cell growth was independently treated in the mathematical model. The proposed growth model agreed well with the experimental data to within 6.6 %, which provides good correlation for both temperature and light intensity effects on the microalgal cell growth.

Variation of photoautotrophic fatty acid production from a highly CO2 tolerant alga, Chlorococcum littorale, with inorganic carbon over narrow ranges of pH

Photoautotrophic fatty acid production of a highly CO2‐tolerant green alga Chlorococcum littorale in the presence of inorganic carbon at 295 K and light intensity of 170 µmol‐photon m−2 s−1 was investigated. 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 surrounding conditions. Maximum content of total fatty acid showed pH‐dependence after nitrate depletion of the culture media and increased with the corresponding inorganic carbon ratio. Namely, [HCO3−]/([CO2]+n[ CO32− ]) ratio in the culture media was found to be a controlling factor for photoautotrophic fatty acid production after the nitrate limitation. At a CO2 concentration of 5% (vol/vol) and a pH of 6.7, the fatty acid content was 47.8 wt % (dry basis) at its maximum that is comparable with land plant seed oils.

Extraction of Functional Lipids from Nannochloropsis sp.

Extraction of functional lipids including eicosapentanoic acid (EPA) from Nannocchloropsis sp. was carried out for ultrasonic extraction, impregnant extraction, and supercritical carbon dioxide extraction with/without ethanol co-solvent. Among the three extraction methods, ultrasonic extraction with both Folch solvent and ethanol led to effective lipid extraction. Although the supercritical fluid extraction with/without ethanol co-solvent gave a low extraction yield of total lipids, EPA was highly concentrated in the extracted triglycerides. (Received Oct. 13, 2017 ; Accepted Dec. 25, 2017)