Mechanism of Copper Stress on Algae Determined Using Mass Spectrometry Molecular Network: Molecular Characteristics and Metabolite Identification

Algae typically respond to environmental changes by regulating the production and release of metabolites that affect water quality and cause various environmental issues. In this study, we investigated the role of algal organic matter (AOM) in copper [Cu(II)] using high-resolution mass spectrometry and a molecular-network-based nontargeted screening. The abundance and activity of algae were inhibited after the addition of Cu(II). Lipids, proteins, lignins, condensed aromatic structures, CHO-only classes, and nitrogenous organic matter are the primary components of AOM. The addition of extracellular organic matter (EOM) and intracellular organic matter (IOM) promoted the generation of carbohydrates that bonded to Cu(II), thus weakening Cu(II) toxicity. Furthermore, 1006 and 589 unique formulas were observed in the Cu(II)-EOM and Cu(II)-IOM groups, respectively, illustrating that EOM and IOM can induce algae to produce different metabolites to resist Cu(II) stress. Six novel phosphatidylethanolamines (PEs) and three novel phosphatidylglycerols (PGs) were identified in the EOM of the Cu(II)-EOM group. Therefore, AOM addition enhanced the synthesis of novel low-unsaturation and palmitoylated PEs, thereby regulating the immune response of algal cells under Cu(II) stress. Overall, these results demonstrated that Cu(II) can perturb lipid utilization and storage, whereas algae can alleviate Cu(II) toxicity by synthesizing and secreting different lipids.