Tetrahymena thermophila transcriptomic responses to silver nanoparticles

Currently, silver nanoparticles (AgNPs) are increasingly used as biocides in various consumer products and if released in the environment they can affect non-target organisms. Therefore, understanding the toxicity mechanism is crucial for both the design of more efficient nano-antimicrobials and for the design of nanomaterials that are biologically and environmentally benign throughout their life-cycle. Here, the ciliate Tetrahymena thermophila was used to elucidate the mechanisms of action of AgNPs by analysing the gene expression profile by RNA-seq. Transcriptomic effects of AgNPs were compared to those induced by soluble silver salt, AgNO3. Exposure to AgNPs at sublethal concentrations for 24 hours induced phagocytosis, transport pathways, response to oxidative stress, glutathione peroxidase activity, response to stimulus, oxidation-reduction, proteolysis, and nitrogen metabolism process. Based on gene set enrichment analysis (GSEA), some biological processes appeared targets of both toxicants. In addition to many similarities in affected genes, some effects were triggered only by NPs, like phagocytosis, glutathione peroxidase activity, response to stimulus, protein phosphorylation and nitrogen metabolism process. This research provides evidence that AgNPs treatment compared to AgNO3 at the same concentration of silver dispersed ions produces a higher response to oxidative stress and affects other different processes. These findings confirm that AgNPs are toxic due to combined effects of soluble silver ions released from particles and particle intrinsic features.