Study of changes in the bioavailability of silver nanoparticles by the bacterial strain Bacillus subtilis

Silver nanoparticles are used in a variety of consumer products, from which they are easily leached. There is a need of better evaluating their toxicity and their fate in the environment. This study is focused on the impact of bacteria and of their secretome (molecules excreted in the medium) on the fate of Ag-Nanoparticles (NPs). We chose a model bacteria present both in the rhizosphere and in the gastro intestinal tractus of mammals, Bacillus subtilis. Bacteria were exposed to pristine Ag-NPs, aged NPs (Ag2S NPs) and ionic Ag at concentrations similar to environmental exposures. These studies are intended to develop the understanding of the main phenomena involved in the biodisponibility of nanomaterials and their secondary products into the rhizosphere. Indeed we have shown that molecules secreted by B. subtilis bind to NPs which affects their hydrodynamic diameter (i.e., the aggregation state). In addition, EXAFS analyses on frozen hydrated cells evidenced major changes in Ag speciation.