Enhancement of non-oleaginous green microalgae Ulothrix for bio-fixing CO₂ and producing biofuels by ARTP mutagenesis

Oleaginous green microalgae are often mentioned in algae-based biodiesel industry, but most of them belong to specific genus (Chlorella, Scenedesmus, Botryococcus and Desmodesmus). Thus, the microalgal germplasm resources for biodiesel production are limited. Mutagenesis is regarded as an important technology for expanding germplasm resources. The main purpose of this study is to screen microalgae strains with high carbon dioxide tolerance and high lipid content from mutants derived from indigenous non-oleaginous green microalgae species-Ulothrix SDJZ-17. Two mutants with high CO₂ tolerance and high lipid content genetic stability were obtained from the mutants by high-throughput screening, named Ulothrix SDJZ-17-A20 and Ulothrix SDJZ-17-A23. In order to evaluate the potential of CO₂ fixation and biofuel production, A20 and A23 were cultured under air and 15% CO₂ (v/v) conditions, and their wild-type strains (WT) were used as controls. Under the condition of high CO₂ concentration, the growth performance and lipid production capacity of mutant strains A20 and A23 were not only significantly better than those of wild strains, but also better than those of their own cultured under air conditions. Among them, A23 obtained the highest LCE (light conversion efficiency) (14.79%), Fv/Fm (maximal photochemical efficiency of photosystem II) (71.04%) and biomass productivity (81.26 mg L^-1 d^-1), while A20 obtained the highest lipid content (22.45%). Both mutants can be used as candidate strains for CO₂ fixation and biofuel production. By ARTP (atmospheric and room temperature plasma) mutagenesis with high-throughput screening, the mutants with higher CO₂ tolerance, photosynthetic efficiency and lipid productivity can be obtained, even if they are derived from non-oleaginous microalgae, which is of great significance for enriching the energy microalgae germplasm bank, alleviating the global warming and energy crisis.