Physiological response and carbon dioxide sequestration mechanisms during photosynthesis in Mychonastes rotundus

Carbon sequestration by microalgae is a simple and easy-to-operate process, without secondary pollution that has broad application prospects due to rapid growth, efficient photosynthesis, and high lipid content produced. In this study, the potential of Mychonastes rotundus for CO2 fixation, and its growth pattern, enzyme activity, lipid production, and cellular microstructure were investigated with changes in CO2 input. The results showed that when the inlet CO2 concentration was 20% (v/v), stable carbon sequestration ability was obtained after a 590 min reaction with an outlet CO2 concentration of 0.32%. The algal cellular structure was intact when the lowest contents of malondialdehyde and reactive oxygen species (ROS) were 7.08 and 17.79 nmol/mg, respectively, indicating the highest cell activity. In addition, 20% CO2 effectively promoted the synthesis of C18:2n6c and C20:0 in M. rotundus. When the inlet CO2 concentration was increased to 30%, the average pH dropped to 5.7, resulting in the death of M. rotundus. 1O2 was identified as the major ROS damaging microalgal cells during carbon sequestration. This study determined the optimal CO2 concentration for carbon capture by M. rotundus as a raw material for biodiesel production. The results indicate that M. rotundus is a promising microalgae for carbon fixation and CO2 capture of power plant flue gas and biodiesel production for low-cost bioenergy production.