Adaptive tolerance to multigenerational silver nanoparticle (NM300K) exposure by the nematode Caenorhabditis elegans is associated with increased sensitivity to AgNO3

Abstract

Toxic effects of silver nanoparticles (Ag NPs) are, in most cases, measured within a single generation, while information regarding multigenerational exposure remains scarce. The current study assessed changes in toxic response (reproduction, fertility, and development) towards Ag NPs (NM300K; uncoated, 16.7 ± 6.5 nm) compared to AgNO3 over six generations, following chronic exposure of the model organism Caenorhabditis elegans. This revealed that AgNO3 exposure was associated with no changes in susceptibility to Ag. In contrast, multigenerational exposure to sub-lethal concentrations of Ag NPs resulted in persistent delayed development, but rendered increased tolerance to Ag NP with respect to fertility and fecundity. The results thus permit inference of a difference in toxic mode of action of the two forms of Ag, which instigate different response patterns. Results reveal a novel mechanism for the adaptation toward Ag NPs, where increased reproductive fitness occurs at the expense of somatic growth. This adaptive mechanism was, however associated with increased susceptibility to AgNO3 with respect to growth, fertility and reproduction. The current study thus demonstrates that a nano-specific resistance can be developed by C. elegans. Importantly, this adaptation renders increased vulnerability to another environmental stressor, and thus exposure to a second contaminant could be detrimental to such populations.