John Wiley & Sons, Ltd.

Silver nanoparticles temporarily retard NO2‐ production without significantly affecting N2O release by Nitrosomonas europaea

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Nitrifying bacteria are highly susceptible to silver nanoparticles (AgNPs). Yet, the effect of sub‐lethal exposure to AgNPs on their release of nitrogenous compounds of environmental concern (e.g., the greenhouse gas nitrous oxide (N2O) and the common water pollutant nitrite (NO2‐)) has not been systematically investigated. Herein, we report the effect of AgNPs (and potentially released silver ions (Ag+)) on NO2‐ and N2O production by Nitrosomonas europaea, and on the transcription of the associated genes. NO2‐ release was more negatively affected than N2O production. For example, exposure to AgNPs at 0.075 mg.L−1 temporarily enhanced N2O production (by 12%) without affecting nitrite release, whereas higher AgNP concentrations (> 0.25 mg.L−1) inhibited NO2‐ release (by > 12%) but not N2O production. Transcriptomic analyses corroborated these trends; AgNPs at 0.075 mg.L−1 increased the expression of the nitric oxide reductase gene (norQ) associated with N2O production (by 5.3‐ to 12.8‐fold), whereas both 0.075 mg.L−1 of Ag+ and 0.75 mg.L−1 of AgNPs down‐regulated the ammonia monooxygenase gene (amoA2) (0.08‐ to 0.15‐fold and 0.32‐ to 0.64‐fold, respectively), the nitrite reductase gene (nirK) (0.01‐ to 0.02‐fold and 0.22‐ to 0.44‐fold, respectively) and norQ (0.11‐ to 0.15‐fold and 0.32‐ to 0.57‐fold, respectively). These results suggest that AgNP release to sewage treatment plants and land‐application of AgNP‐containing biosolids should be minimized due to their potential temporary stimulation of N2O release and interference with nitrification. This article is protected by copyright. All rights reserved

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