Adaptive laboratory evolution of extremophilic red microalga Cyanidioschyzon merolae under high nickel stress enhances lipid production and alleviates oxidative damage

Abstract

The extremophilic red microalga Cyanidioschyzon merolae suffers irreversible photosynthetic damage, oxidative stress, and apoptosis when exposed to Ni concentrations above 3 mM. To enhance Ni tolerance, we applied adaptive laboratory evolution (ALE) and developed a robust strain capable of thriving at 10 mM Ni. The novel strain, dubbed 10NiLAD ( 10 mM Ni L ong-term Ad apted), exhibited growth, photosynthetic performance, as well as pigment and ATP content comparable to the wild type (WT), with c -phycocyanin content reaching 197 mg g −1 . 10NiLAD strain accumulated lipids as cytoplasmic droplets with increased saturated fatty acids content, and showed significantly enhanced Ni biosorption (15 mg g −1 ). Notably, it produced significantly less reactive oxygen species than the WT, likely due to increased superoxide dismutase activity, suggesting a key role for this enzyme in oxidative stress mitigation under Ni stress. These results demonstrate the potential of ALE to generate metal-hyper resistant microalgal strains suitable for biotechnological applications in extreme environments.