Development of UV-induced mutants of Scenedesmus obliquus with enhanced lipid content for sustainable biofuel production.

The commercial viability of microalgal biofuels is currently hindered by challenges in achieving high-yield biomass and lipid productivity. To address these limitations, this study employed UV-induced random mutagenesis to generate superior lipid-producing strains of Scenedesmus obliquus. Following mutagenesis and screening under nitrogen-deficient conditions, two mutant strains, SOM11 and SOM05, exhibited significantly enhanced lipid accumulation, reaching 0.52 gL⁻¹ and 0.55 gL⁻¹, respectively, compared to 0.4 gL⁻¹ for the wild-type. Quantitative analysis using Nile red fluorescence microscopy confirmed the presence of higher cytoplasmic lipid bodies in the mutants, with SOM11 and SOM05 exhibiting 43% and 6% greater fluorescence intensity, respectively, compared to the wild-type. Further characterization of the fatty acid methyl ester (FAME) profiles by GC-MS revealed that both mutants produced more total FAMEs. Notably, the mutants exhibited a more diverse fatty acid composition, including C18:0 and C20:5, compared to the wild-type's profile, which was dominated by C16:0 and C18:1. This altered profile is advantageous for improving biofuel quality. Principal Component Analysis confirmed distinct metabolic differences, with the primary component accounting for 53.5% of the variance between mutant and wild-type strains. Gene expression analysis via RT-PCR identified a significant upregulation of key lipid biosynthesis genes, acetyl-CoA carboxylase (ACC) and 3-oxoacyl-acyl carrier protein reductase (FabG), in the SOM11 strain by 9.14-fold and 4.43-fold, respectively. These results indicate that UV mutagenesis successfully modulated critical metabolic pathways, leading to the high-lipid phenotype. This work demonstrates that UV mutagenesis is an effective strategy for developing improved S. obliquus strains for sustainable biofuel production.