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

Abstract

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.

Keywords: Ulothrix; ARTP mutagenesis; High CO2 tolerance; Lipid content; Photosynthetic efficiency.

Fig. 1

Ulothrix SDJZ-17 wild strain (WT) and mutant strains (A1, A2,…… A43) relative neutral lipid fluorescence intensities

Fig. 2

Genetic stability of Ulothrix SDJZ-17 candidate mutants (A6, A20, A23, A29 and A30) in growth (a–e) and total lipid accumulation (f) under high CO₂ concentration

Fig. 3

Growth curves of Ulothrix SDJZ-17 wild type (WT) and mutant strains (A20 and A23) under air and 15% (v/v) CO₂ conditions for 7 days (each data is expressed as mean ± standard deviation from three independent cultures)

Fig. 4

Total lipid, total carbohydrate and crude protein content (a) and biomass, total lipid, total carbohydrate and crude protein productivities (b, mg L⁻¹ d⁻¹) of Ulothrix SDJZ-17 wild-type strain (WT) and mutant strains (A20 and A23) cultured in air and 15% (v/v) CO₂ for 7 days. Each data was expressed as the mean ± standard deviation of the three independent cultures, and the same component was marked with different letters, indicating that the results were significantly different by the Duncan test (p < 0.05)