Selenium Alleviates Mercury Toxicity in Ophiocordyceps sinensis: Mechanistic Insights from Integrated Phenotypic and Transcriptomic Analyses

Ophiocordyceps sinensis, a valuable medicinal and nutritional resource, faces significant mercury (Hg) contamination risks. Total Hg content in some samples from key producing regions exceeds the 0.2 mg/kg limit set by the Chinese Pharmacopoeia, raising ecological and food safety concerns. To investigate whether and how sodium selenite (Na2SeO3) alleviates mercury (II) chloride (HgCl2) toxicity, this study established various concentrations for Hg, Se, and combined Hg + Se treatments. Results showed that Hg stress significantly inhibited mycelial growth, reducing fresh weight by 38% at 1 mg/L and by up to 98% at high concentrations, whereas Hg + Se treatment increased mycelial dry weight and ameliorated morphological damage relative to Hg treatment alone. Furthermore, Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS) analyses confirmed the formation of Hg-Se bonds and stable complexes such as HgSe, HgSeO3, and HgSeO4 in the Hg + Se group, constituting the key material basis for Se-mediated Hg detoxification. Hg stress induced ROS accumulation, with O2−· peaking at 3.96 nmol/g and GSH at 4.86 μg/g under 2 mg/L Hg; exogenous Se reduced O2−· accumulation by 37%. Soluble sugar increased continuously with Hg concentration, while soluble proteins increased continuously under Hg + Se treatment. Transcriptome analysis indicated that Se alleviated Hg-induced transcriptomic disturbances by modulating genes associated with tyrosine metabolism (TYR), peroxisome function (CAT), and glucose metabolism (tktA, rpiA). In conclusion, Se alleviates Hg toxicity in O. sinensis through the synergistic actions of chemical chelation and metabolic regulation, offering new insights into Hg mitigation in artificial cultivation.