Currently, silver nanoparticles are increasingly used as biocides in various consumer products and if released in the environment they can affect non-target organisms. Nanoparticles are defined as particles with at least one dimension between 1 and 100 nm. The specific surface area increases in reversal proportion to the particle size; thus, the smaller the particle, the greater the proportion of atoms that lay close to or at the surface resulting in higher reactivity of the particle. These properties, which make nanomaterials more efficient in industrial applications, might make them also more harmful to living organisms since they could be able to penetrate physiological barriers, travel throughout the body and interact with subcellular structures. Therefore, understanding the toxicity mechanisms is crucial for both the design of more efficient nano-antimicrobials and, at the same time, for the design of nanomaterials that are biologically and/or environmentally benign throughout their life-cycle.
Tetrahymena thermophila has been largely investigated and functional genomic databases are available. Therefore, T. thermophila provides an optimal model system for studying molecular bases of environmental responses, since molecular data obtained in different environmental conditions can be easily compared. We recently used T. thermophila to elucidate the environmental effects of silver nanoparticles by analysing T. thermophila’s gene expression profile by RNA-seq after exposure to collargol (protein-stabilized silver nanoparticles) and comparing with the effect of the soluble silver salt, AgNO3. In order to see the effects of these substances in viable cells, only sub-lethal concentrations are used in gene expression studies. We tested two different toxicant concentrations at two time points, for 2 and 24 hours.
The experimental sequences are compared with the control to evaluate quantitatively the inhibition or increase of gene expression due to nanoparticles or silver ions. Then gene set enrichment is performed.
Some processes are targets of both toxicants. In addition to many similarities in affected genes, some effects were different for soluble silver ion with respect to collargol. We found that genes involved in mRNA splicing and translation processes appear differentially expressed only in collargol treated samples.
This research provides evidence that silver nanoparticles might be toxic due to combined effects of soluble silver ions released from the particles and the particles themselves.