Photoautotrophic Growth and Cell Division of Euglena gracilis with Mixed Red and Blue Wavelengths

To improve flue gas CO2 fixation of Euglena gracilis under a photoautotrophic environment, mixed red and blue wavelengths were used to promote photosynthetic growth and cell division with 15% CO2. The biomass dry weight increased by 385% to 1.31 g/L with a peak ribulose-1,5-bisphosphate carboxylase/oxygenase enzyme activity and oxygen release, when the ratio of red to blue wavelength decreased to 2:3. E. gracilis mainly engaged in photochemical reactions with accumulated photosynthetic pigment to focus on light conversion by optimizing the carotenoid/chlorophyll ratio and chlorophyll a/b ratio. The energy capture efficiency of open photosystem II (PSII) reaction centers and quantum efficiency of charge separation in PSII reaction centers were improved to maintain active photosynthesis. Blue light facilitated transition from G1 to S phase, while red light promoted transition from S to G2 phase. The malondialdehyde content decreased to a valley of 1.36 nmol/mg protein to keep efficient photosynthetic apparatus with carbon fixation.