title: Sublethal concentrations of silver nanoparticles affect the mechanical stability of biofilms.
abstract: Bacterial biofilms are most likely confronted with silver nanoparticles (Ag NPs) as a pollutant stressor in aquatic systems. In this study, biofilms of Aquabacterium citratiphilum were exposed for 20 h to 30 and 70 nm citrate stabilized Ag NPs in low-dose concentrations ranging from 600 to 2400 μg l-1, and the Ag NP-mediated effects on descriptive, structural, and functional biofilm characteristics, including viability, protein content, architecture, and mechanical stability, were investigated. Viability, based on the bacterial cell membrane integrity of A. citratiphilum, as determined by epifluorescence microscopy, remained unaffected after Ag NP exposure. Moreover, in contrast to information in the current literature, protein contents of cells and extracellular polymeric substances (EPS) and biofilm architecture, including dry mass, thickness, and density, were not significantly impacted by exposure to Ag NPs. However, the biofilms themselves served as effective sinks for Ag NPs, exhibiting enrichment factors from 5 to 8. Biofilms showed a greater capacity to accumulate 30 nm sized Ag NPs than 70 nm Ag NPs. Furthermore, Ag NPs significantly threatened the mechanical stability of biofilms, as determined by a newly developed assay. For 30 nm Ag NPs, the mechanical stability of biofilms decreased as the Ag NP concentrations applied to them increased. In contrast, 70 nm Ag NPs produced a similar decrease in mechanical stability for each applied concentration. Overall, this finding demonstrates that exposure to Ag NPs triggers remarkable changes in biofilm adhesion and/or cohesiveness. Because of biofilm-mediated ecological services, this response raises environmental concerns regarding Ag NP release into freshwater systems, even in sublethal concentrations.
authors.affiliation: Institute for Integrated Natural Sciences, University of Koblenz-Landau, Universitätsstr. 1, 56070, Koblenz, Germany. alexg@uni-koblenz.de.
authors.forename: Alexandra Y
authors.initials: AY
authors.lastname: Grün
authors.affiliation: Institute for Integrated Natural Sciences, University of Koblenz-Landau, Universitätsstr. 1, 56070, Koblenz, Germany.
authors.forename: Jutta
authors.initials: J
authors.lastname: Meier
authors.affiliation: Institute for Environmental Sciences, Group of Environmental and Soil Chemistry, University of Koblenz-Landau, Fortstr. 7, 76829, Landau, Germany.
authors.forename: George
authors.initials: G
authors.lastname: Metreveli
authors.affiliation: Institute for Environmental Sciences, Group of Environmental and Soil Chemistry, University of Koblenz-Landau, Fortstr. 7, 76829, Landau, Germany.
authors.forename: Gabriele E
authors.initials: GE
authors.lastname: Schaumann
authors.affiliation: Institute for Integrated Natural Sciences, University of Koblenz-Landau, Universitätsstr. 1, 56070, Koblenz, Germany.
authors.forename: Werner
authors.initials: W
authors.lastname: Manz
mesh_terms: D000327:Adsorption; D001426:Bacterial Proteins / Q000378:metabolism; D020562:Betaproteobacteria / Q000187:drug effects* / Q000254:growth & development; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D002462:Cell Membrane / Q000187:drug effects; D019343:Citric Acid / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D053768:Metal Nanoparticles / Q000737:chemistry / Q000633:toxicity*; D050296:Microbial Viability / Q000187:drug effects; D010316:Particle Size; D012834:Silver / Q000737:chemistry / Q000633:toxicity*; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000633:toxicity*
chemical_list: D001426:Bacterial Proteins; D014874:Water Pollutants, Chemical; D019343:Citric Acid; D012834:Silver
keywords: Aquabacterium citratiphilum; Mechanical stability; Nanoparticle enrichment; Silver nanoparticles; Toxicity; monospecies biofilm