Improved lipid production in Chlorella sp. UJ-3 using Fe3O4 nanoparticles assisted by an alternating magnetic field and transcriptome analysis

In this study, a process intensification strategy combining magnetic Fe₃O₄ nanoparticles (NPs) and an alternating magnetic field (MF) was employed to enhance lipid production in Chlorella sp. UJ-3. Among the tested MFs at various frequencies, the alternating MF at 200 Hz demonstrated the most significant promotion of cell growth and lipid production. Under this treatment, biomass increased by 64.5 %, and total lipid production was enhanced by 170.8 % compared to the untreated control. With the MF and Fe₃O₄ NPs treatment, algal cells regulated their antioxidant defense system, resulting in increased activities of related antioxidant enzymes to counteract the elevated reactive oxygen species induced by the MF and Fe₃O₄ NPs. The regulatory mechanism of Fe₃O₄ NPs on Chlorella sp. metabolism under a MF was analyzed at the transcriptome level. The addition of Fe₃O₄ NPs promoted the synthesis and desaturation of fatty acids while reducing their β-oxidation. The expression of most enzyme genes in the glycolytic pathway were downregulated, while several enzyme genes in the pentose phosphate pathway were upregulated. The expression of superoxide dismutase and catalase genes was also upregulated under Fe₃O₄ NPs treatment. This study provides an efficient method for enhancing lipid production in microalgal cells and offers valuable insights into the biological effects of magnetic NPs on algal metabolism.