Pseudomonas putida biofilm dynamics following a single pulse of silver nanoparticles

• Mature Pseudomonas putida mono-species biofilms were cultured under hydrodynamic conditions.
• Short and long term impacts of Ag NPs on biofilm morphology, viability and activity were studied.
• Dose dependent toxicity patterns were reported post exposure to 0.01–100 mg L−1.
• Recovering biofilms were characterised 24 h post exposure.
• Dynamic biofilm based models offer enhanced nanosafety assessment.

Pseudomonas putida mono-species biofilms were exposed to silver nanoparticles (Ag NPs) in artificial wastewater (AW) under hydrodynamic conditions. Specifically, 48 h old biofilms received a single pulse of Ag NPs at 0, 0.01, 0.1, 1, 10 and 100 mg L−1 for 24 h in confocal laser scanning microscopy (CLSM) compatible flow-cells. The biofilm dynamics (in terms of morphology, viability and activity) were characterised at 48, 72 and 96 h. Consistent patterns were found across flow-cells and experiments at 48 h. Dose dependent impacts of NPs were then shown at 72 h on biofilm morphology (e.g. biomass, surface area and roughness) from 0.01 mg L−1. The microbial viability was not altered below 10 mg L−1 Ag NPs. The activity (based on the d-glucose utilisation) was impacted by concentrations of Ag NPs equal and superior to 10 mg L−1. Partial recovery of morphology, viability and activity were finally observed at 96 h. Comparatively, exposure to Ag salt resulted in ca. one order of magnitude higher toxicity when compared to Ag NPs. Consequently, the use of a continuous culture system and incorporation of a recovery stage extends the value of biofilm assays beyond the standard acute toxicity assessment.

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