Cadmium Accumulation and Regulation in the Freshwater Mussel Anodonta woodiana

Abstract

Cadmium (Cd) pollution poses a serious threat to freshwater ecosystems. The freshwater mussel Anodonta woodiana is increasingly used as a bioindicator for monitoring Cd pollution in aquatic environments. However, the primary routes of Cd accumulation in A. woodiana remain unclear, and the molecular regulatory mechanisms underlying Cd accumulation are poorly understood. To address these gaps, this study employed a novel stable isotope dual-tracer technique to trace Cd from water (waterborne ¹¹²Cd) and the green alga Chlorella vulgaris (dietary ¹¹³Cd) during the simultaneous exposure experiment. Comparative transcriptomic analysis was then conducted to characterize molecular responses in A. woodiana following Cd exposure. The results showed that although newly accumulated ¹¹²Cd and ¹¹³Cd increased with exposure concentration and duration, the relative importance of ¹¹²Cd (91.6 ± 2.8%) was significantly higher than that of ¹¹³Cd (8.4 ± 2.8%) (p < 0.05). Cd exposure induced differentially expressed genes primarily enriched in the metabolic processes, cellular processes, and/or the ubiquitin-mediated proteolysis pathway. Within the ubiquitin-mediated proteolysis pathway, TRIP12 (E3 ubiquitin-protein ligase TRIP12) and Cul5 (cullin-5) were significantly upregulated. The findings will provide critical insights for interpreting Cd biomonitoring data in freshwater environments using mussels as bioindicators.

Keywords: Anodonta woodiana; bioaccumulation; cadmium; molecular regulatory; stable isotope dual-tracer technique; transcriptome.

Figure 1

The newly accumulated ¹¹²Cd (A) and ¹¹³Cd (B) in Anodonta woodiana simultaneously exposed to waterborne ¹¹²Cd and dietary ¹¹³Cd over 30 d (n = 3). T1 refers to 2.5 μg L⁻¹ waterborne ¹¹²Cd and 1.9 μg g⁻¹ dw dietary ¹¹³Cd simultaneous exposure (green); T2 refers to 5.3 μg L⁻¹ waterborne ¹¹²Cd and 3.7 μg g⁻¹ dw dietary ¹¹³Cd simultaneous exposure (blue); and T3 refers to 10.8 μg L⁻¹ waterborne ¹¹²Cd and 6.2 μg g⁻¹ dw dietary ¹¹³Cd simultaneous exposure (red). Values with different letters indicate a significant difference (p < 0.05).

Figure 2

(A) Differentially expressed genes (DEGs) induced by waterborne Cd exposure at 2.5 μg L⁻¹ (low concentration, LC), 5.0 μg L⁻¹ (medium concentration, MC), and 50 μg L⁻¹ (high concentration, HC) in Anodonta woodiana for 10 d compared to the control group (0 μg L⁻¹, CK); (B) RNA-Seq and (C) RT-qPCR validation of relative expression levels for the genes TubB (Tubulin beta chain), PhoA (Phospholipase A1 magnifin), PheT (Phenylalanine-tRNA ligase), and ProH (Protein henna); and (D) KEGG pathway analysis of DEGs. Superscript asterisks indicate significant differences between the Cd-treated and control groups (p < 0.05).