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

Abstract

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 has not adequately explored biofilms, which serve as the predominant mode of bacterial growth in natural and engineered environments. Copper nanoparticle (Cu-NP) impacts on biofilms were compared with respective planktonic cultures of the ammonium-oxidizing Nitrosomonas europaea, nitrogen-fixing Azotobacter vinelandii, and denitrifying Paracoccus denitrificans using a suite of independent toxicity diagnostics. Median inhibitory concentration (IC50) values derived from adenosine triphosphate (ATP) 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, compared with 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-fold to 50-fold less inhibited than those in planktonic cells. Physiological evaluation of ammonium oxidation and nitrate reduction suggested that 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 that nitrogen-cycling bacteria in wastewater, wetlands, and soils might be more resilient to NPs than planktonic-based assessments suggest.

Size-dependent cytotoxicity of silver nanoparticles to Azotobacter vinelandii: Growth inhibition, cell injury, oxidative stress and internalization

“…Yu et al [22] studied the toxicity of four widely used NPs (TiO 2 , SiO 2 , Ag and CdTe/CdS) to Chlamydomonas reinhardtii and found different cytotoxicity effects. Reyes et al [29] revealed that growth rate of A . vinelandii biofilms was significantly reduced as exposed to CuNPs.…”

Impacts of metal-based engineered nanomaterials on soil communities

“…Differences between the three species' reactions were also related to species traits such as speed of growth and nutrient requirements. 140 In activated sewage sludge, nitrifying bacteria were compromised both in enzyme activity and abundance by SiO 2 NP, yet only at high concentration 126 (Table 3). García et al 9 observed that CeO 2 NP andconsiderably less -AuNP reduced the activity of ammonifying bacteria in a wastewater treatment plant, whereas no such effects were seen for TiO 2 -NP and AgNP.…”

The antimicrobial activity of nanoparticles: present situation and prospects for the future

“…In particular, biofilms are less restrained by antibacterial agents than the respective planktonic bacteria are. 8 Nanomaterials are materials that have at least one dimension (1-100 nm) in the nanometer scale range or whose basic unit in the three-dimensional space is in this range. 9 NPs in particular have demonstrated broad-spectrum antibacterial properties against both Gram-positive and Gram-negative bacteria.…”