Functional validation and mechanistic insights into cadmium removal by the green microalgae Coelastrella tenuitheca...

Cadmium (Cd), a toxic heavy metal resistant to environmental degradation, requires eco-friendly remediation strategies. This study evaluated the efficacy of microalgae species in Cd removal, identifying Coelastrella tenuitheca S93-3 as the most efficient, achieving ‌94.87% removal efficiency at 30 mg/L CdCl₂ exposure. This removal was primarily achieved through biosorption, binding 48% of Cd to the cell wall, and biotransformation, converting ∼30% into less toxic forms within the cells. Genomic and transcriptomic analyses revealed differential regulation of Cd uptake (ZIP, Sbp, HMA, ABC) and biotransformation genes linked with sulfur assimilation and cysteine/methionine metabolism, thereby enhancing glutathione synthesis for Cd-phytochelatins complexation and detoxification. Metabolomic profiling identified 13-fold increased aminolevulinic acid, which contributes to Cd tolerance by stabilizing key cellular pathways such as porphyrin metabolism and TCA cycle. The reduction in Cd uptake and translocation by S93-3 was further validated in hydroponically grown rice and lettuce, leading to improved plant growth and reduced oxidative stress, while modulating the expression of Cd uptake and detoxification genes. This study provides both theoretical foundations and practical strategies for eco-friendly heavy metal bioremediation.