Effects of selenite on growth and metabolism in Chlamydomonas reinhardtii

Selenium (Se) is an essential trace element for humans and animals, playing a pivotal role in antioxidant defense, immune regulation, and disease prevention. Chlamydomonas reinhardtii is considered a promising edible source for selenium-enriched food production. Yet, its mechanisms of selenium tolerance and metabolic regulation remain insufficiently understood, limiting the optimization of biofortification strategies. This study used the C. reinhardtii strain RZTCr-1 to elucidate the concentration-dependent effects of sodium selenite on its growth, photosynthesis, and selenium metabolic pathways. The results demonstrated that low concentrations of sodium selenite (<6 mg/L) had no significant impact on growth or photosynthetic efficiency, whereas concentration higher than 6 mg/L markedly suppressed photosynthesis. Sodium selenite treatment significantly upregulated the expression of selenoprotein genes and enhanced antioxidant enzyme activities. Electron microscopy combined with EDX spectral analysis confirmed the formation of nano‑selenium particles under high sodium selenite concentrations. Transcriptomic analysis revealed that 6 mg/L sodium selenite significantly repressed the expression of photosynthesis-related genes, and reduced energy production, but simultaneously activated proteasome and autophagy pathways, promoting catabolic metabolism. This study identifies 6 mg/L as the critical threshold at which sodium selenite inhibits photosynthesis while enhancing catabolic processes in C. reinhardtii , providing a theoretical basis for selenium-enriched microalgae production and laying the foundation for targeted manipulation of algal selenium metabolic pathways. • The impact of selenite on the growth and metabolism of C. reinhardtii was detected. • Selenite enhanced selenoprotein genes expression and antioxidant enzyme activities. • SeNPs were observed under high sodium selenite concentrations. • Selenium influenced multiple metabolic pathways and signal transduction processes.