Caenorhabditis elegans in nanosafety research: dual effect of Escherichia coli ecocorona formation on single and combined toxicity of graphene oxide.

Caenorhabditis elegans is a free-living nematode widely applied in nanosafety research. It feeds primarily on organic matter, with bacteria as its primary nutrient source. Under experimental conditions, Escherichia coli is routinely provided as food to prevent starvation in C. elegans. However, its influence on C. elegans' biological responses to nanomaterials remains unexplored. This study investigated the implications of E. coli ecocorona formation on the physicochemical properties, colloidal behaviour and toxicity of graphene oxide (GO), both individually and combined with silver ions (Ag+), in the C. elegans model. Using a multi-technique approach, we observed significant changes in GO's topography, surface roughness, chemical composition, and colloidal stability, indicating that E. coli biomolecules coated the GO surface selectively. Notably, the ecocorona mitigated GO toxicity, as it suppressed lethality and neuronal injuries induced by GO while also reducing adverse effects on the germline and hindering the direct contact of GO with the intestinal barrier. In contrast, the combination of ecocorona-coated GO (EC@GO) with Ag+ aggravated Ag+ lethality by 460%, and was the most damaging treatment to neurons and reproductive organs. Organisms exposed to EC@GO with Ag+ accumulated twice as much Ag as those exposed to bare GO with Ag+, indicating that the ecocorona acted as a carrier of silver. These outcomes provide the first evidence of the dual effect of the E. coli ecocorona in modulating the individual and combined toxicity of GO, underscoring the importance of the C. elegans research community implementing routine characterization of the E. coli ecocorona as a prerequisite in nanosafety assessments.