Heterogeneous Single-Cell Distribution of Trace-Level Metal Mixtures in <i>Tetrahymena thermophila</i> Using Mass Cytometry

The uptake of heavy metals by unicellular organisms can lead to the bioaccumulation of these metals in higher organisms, detrimentally affecting organismal health and ultimately impacts the ecosystems. By studying the uptake and accumulation of heavy metals in unicellular organisms, we gain insights into potential risks associated with low-dose heavy metal exposure in aquatic environments. Thus, to investigate the accumulation characteristics of Mo, Ag, Cd, Sn, Sb, Hg, Tl, and Pb mixtures in single <i>Tetrahymena thermophila</i> cells, we developed a label-free approach for the simultaneous absolute quantification of multiple metals in a single cell using mass cytometry. Our results demonstrated the dynamic changes in metal concentrations in <i>T. thermophila</i>, and the competition between metals in uptake and excretory pathways resulted in heterogeneous accumulation and bioconcentration of these metals. Additionally, our findings revealed the limited capacity of <i>T. thermophila</i> to excrete Cd and Hg, suggesting a higher risk for <i>T. thermophila</i> cells when exposed to Cd and Hg over an extended period. Therefore, the current study provides valuable data for a more comprehensive understanding of the impact of low-dose heavy metals on aquatic ecosystems.