<scp>ApCaleosin</scp> resists cadmium stress by regulating lipid droplet formation and intracellular oxidative stress levels in microalgae

Microalgae are considered a promising candidate for cadmium biosorption material. However, the mechanisms behind their resistance to cadmium remain unclear. Here, we have uncovered that a lipid droplet (LD) protein caleosin of Auxenochlorella protothecoides regulates Cd tolerance in microalgae. The expression level of ApCaleosin significantly increases under Cd stress. ApCaleosin overexpression strain showed reduced sensitivity to cadmium, while the ApCaleosin knockdown resulted in increased sensitivity. Furthermore, ApCaleosin functions as a peroxygenase to alleviate oxidative stress through heteroexpression in Escherichia coli, which is a calcium-dependent process. Additionally, by supplementing ApCaleosin in yeast knockout strains, we discovered that ApCaleosin can promote an increase in LD numbers, thereby wrapping more cadmium ions and reducing cellular cadmium toxicity. These findings reveal the specific mechanism of microalgae's resistance to cadmium, offering new prospects for enhancing bioremediation efficiency.