Blue Light Reprograms Fatty Acid Metabolism in Scenedesmus sp. GSB9 Revealed by Integrated Transcriptomics and Metabolomics

Scenedesmus sp. GSB9, a freshly isolated fast-growing microalgal strain derived from wastewater, was cultivated under continuous white, blue, and sequential blue-to-red (9B3R) light regimes to investigate light-quality–mediated regulation of fatty acid biosynthesis. Integrated multi-omics analysis, combining de novo transcriptomics, LC–HRMS metabolomics, and GC–FID fatty acid profiling, revealed that blue light enhanced the metabolic landscape, including higher palmitic acid accumulation. Additionally, this response was complemented by enrichment of triglyceride biosynthetic pathways (GO:0019432) and upregulation of Acetyl-CoA carboxylase (ACCase), which encodes a key enzyme that catalyzes the conversion of acetyl-CoA to malonyl-CoA for de novo fatty acid synthesis, and was supported by RT-qPCR validation of selected genes. In contrast, the 9B3R regime induced global transcriptional activation of stress-responsive metabolic pathways, including DNA repair (GO:0006281) and protein folding (GO:0006457), along with central carbon metabolism and reduced lipid accumulation. This divergence suggests a decoupling between transcriptional activity and metabolic output under dynamic light transitions, potentially mediated by post-transcriptional or post-translational regulation. Collectively, these findings indicated continuous blue light as a driver of lipid accumulation in Scenedesmus sp. GSB9 and identified key regulatory nodes for optimizing light-driven metabolic engineering and scalable microalgal bioprocesses.