Distinct transcriptomic responses of Caenorhabditis elegans to pristine and sulfidized silver nanoparticles

Manufactured nanoparticles (MNP) rapidly undergo aging processes once released from products. Silver sulfide (Ag₂S) is the major transformation product formed during the wastewater treatment process for Ag-MNP. We examined toxicogenomic responses of pristine Ag-MNP, sulfidized Ag-MNP (sAg-MNP), and AgNO₃ to a model soil organism, Caenorhabditis elegans. Transcriptomic profiling of nematodes which were exposed at the EC₃₀ for reproduction for AgNO₃, Ag-MNP, and sAg-MNP resulted in 571 differentially expressed genes. We independently verified expression of 4 genes (numr-1, rol-8, col-158, and grl-20) using qRT-PCR. Only 11% of differentially expressed genes were common among the three treatments. Gene ontology enrichment analysis also revealed that Ag-MNP and sAg-MNP had distinct toxicity mechanisms and did not share any of the biological processes. The processes most affected by Ag-MNP relate to metabolism, while those processes most affected by sAg-MNP relate to molting and the cuticle, and the most impacted processes for AgNO₃ exposed nematodes was stress related. Additionally, as observed from qRT-PCR and mutant experiments, the responses to sAg-MNP were distinct from AgNO₃ while some of the effects of pristine MNP were similar to AgNO₃, suggesting that effects from Ag-MNP is partially due to dissolved silver ions.