Screening temperature-tolerant and high-yield Spirulina maxima mutants using ¹²C⁶⁺ ion beam irradiation and optimizing its culture conditions

Spirulina maxima (S. maxima) was irradiated using ¹²C⁶⁺ ion beams at different doses, and the mutant strains were selected by plate separation and temperature treatment methods. Mutant strains with high biomass yields and increased temperature tolerance were screened out by genetic stability analysis. The culture conditions of the mutants were also optimized. Results showed that when the absorbed doses were 600 Gy and 800 Gy, the mutagenic effects on the algae strains were significant and the mortality rates were 71.84% and 78.47%, respectively. Two temperature-tolerant mutants (Sm04⋕ and Sm21⋕) were obtained, which were cultured at 20℃ and 35℃ after irradiation at 600 Gy and 800 Gy. After ten generations, the biomasses of the mutants were 0.54 g/L and 0.91 g/L, respectively, which were 11.49% and 12.64% larger than the biomass of the control group, respectively. The culture conditions optimization experiment indicated that the optimum pH of both Sm04⋕ and Sm21⋕ was 9.0, the optimum light intensities were 70 and 80 μmol/(m² · s), respectively, and the optimum light-dark periods were 12:12 h and 14:10 h, respectively. In addition, the protein and polysaccharide contents of the two mutants were both higher than those of the control group, which provides a theoretical basis for the development and application of S. maxima using carbon ion irradiation. (authors)