John Wiley & Sons, Ltd.

Planktonic and biofilm grown nitrogen cycling bacteria exhibit different susceptibilities to copper nanoparticles

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Proper characterization of nanoparticle (NP) interactions with environmentally relevant bacteria under representative conditions is necessary to enable their sustainable manufacture, use, and disposal. Previous nanotoxicology research based on planktonic growth does not adequately explore biofilms, which serve as the predominant mode of bacterial growth in natural and engineered environments. Herein, copper nanoparticle (Cu‐NP) impacts to biofilms were compared to respective planktonic cultures of the ammonium oxidizing Nitrosomonas europaea, nitrogen‐fixing Azotobacter vinelandii, and denitrifying Paracoccus denitrificans using a suite of independent toxicity diagnostics. ATP‐derived IC50 values for Cu‐NPs were lower in N. europaea biofilms (19.6 ± 15.3 mg/L) than in planktonic cells (49.0 ± 8.0 mg/L). However, in absorbance based growth assays, when compared to unexposed controls, N. europaea growth rates in biofilms were twice as resilient to inhibition than those in planktonic cultures. Similarly relative to unexposed controls, growth rates and yields of P. denitrificans in biofilms exposed to Cu‐NPs were 40‐50 fold less inhibited than those in planktonic cells. Physiological evaluation of ammonium oxidation and nitrate reduction suggested biofilms were also less inhibited by Cu‐NPs than planktonic cells. Furthermore, functional gene expression for ammonium oxidation (amoA) and nitrite reduction (nirK) showed lower inhibition by NPs in biofilms relative to planktonic grown cells. These results suggest that biofilms mitigate NP impacts, and than nitrogen‐cycling bacteria in wastewater, wetlands, and soils might be more resilient to NPs than planktonic‐based assessments suggest. This article is protected by copyright. All rights reserved

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