# Using Sodium Thiosulfate to Heighten Copper (Cu (II)) Tolerance of the Freshwater Microalga Chlorella vulgaris

## TL;DR

Sodium thiosulfate helps a freshwater microalga survive copper pollution by boosting its tolerance through changes in photosynthesis and metabolism.

## Contribution

A novel bioremediation strategy using sodium thiosulfate to enhance microalgal tolerance to copper pollution.

## Key findings

- Sodium thiosulfate and copper co-stress significantly improves Chlorella vulgaris tolerance to Cu(II).
- 103 differentially expressed genes linked to photosynthesis, energy, and lipid metabolism were identified.
- Physiological metrics confirmed gene expression findings, showing improved stress responses.

## Abstract

This study demonstrates that sodium thiosulfate (Na2S2O3) enhances copper (Cu(II)) tolerance in the microalga Chlorella vulgaris. Integrated gene expression and physiological analyses reveal that the improved tolerance involves coordinated regulation of key processes in photosynthesis, energy metabolism, and lipid metabolism. These findings provide a potential bioremediation strategy targeting copper-contaminated aquatic environments.

Heavy metals such as copper are commonly found in aquatic environments. Microalgae can effectively adsorb heavy metals, while high concentrations impair their physiological and biochemical processes. This research investigated the impact of varying concentrations of sodium thiosulfate (Na2S2O3) on the heavy metal tolerance of Chlorella vulgaris. Results showed that Na2S2O3 and copper ions Cu(II) co-stress significantly improved the tolerance of C. vulgaris to Cu(II). To explore the mechanism, weighted gene co-expression network analysis (WGCNA) and trend analysis were applied to study the gene regulatory network under combined stress. A total of 103 significantly differentially expressed genes (DEGs) were identified. Further Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that the majority of DEGs are associated with photosynthesis, energy and liposome metabolisms. Physiological metrics, including chlorophyll content, photosynthetic activity, malondialdehyde (MDA), superoxide dismutase (SOD), and catalase (CAT), also aligned with bioinformatics results. This research offers a promising approach to reduce heavy metal pollution in water bodies.