Interactions of silver nanoparticles with Pseudomonas putida biofilms

Silver nanoparticles (Ag NPs) may present a risk to the environment due to their expected toxicity and wide exposure. The interactions between Ag NPs and laboratory-grown Pseudomonas putida biofilms were investigated under a range of environmentally relevant conditions (pH 6 and 7.5; presence and absence of Suwannee River fulvic acid (SRFA)) over 4 days. In the absence of SRFA, there was extensive sloughing of the biofilm bacteria into suspension implying NP-bacterial interactions and potential effects on NP transport in the environment. In the presence of SRFA, sloughing of cells into suspension was reduced under some conditions and Ag NPs and their aggregates were observed and quantified on and in the bacterial cells in the biofilm. Viability of the cells in all cases appear unchanged by the presence of Ag NPs. Cell viability was independent of the concentration of NPs in solution, but sloughing rates varied substantially, sometimes in a dose-dependent manner. The results suggest that biofilms are impacted by Ag NPs when SRFA was not present, and that SRFA increases uptake and bioaccumulation of Ag NPs to biofilms, perhaps resulting in longer term effects, which need further investigation.