title: Effects of sublethal doses of silver nanoparticles on Bacillus subtilis planktonic and sessile cells.
abstract: OBJECTIVE
  Due to their antimicrobial activity, silver nanoparticles (Ag-NPs) are being increasingly used in a number of industrial products. The accumulation of Ag-NPs in the soil might affect plant growth-promoting rhizobacteria and, in turn, the plants. We describe the effects of Ag-NPs on the soil bacteria Azotobacter vinelandii and Bacillus subtilis.
  
  
  RESULTS
  In growth-inhibition studies, A. vinelandii showed extreme sensitivity to Ag-NPs, compared to B. subtilis. We investigated the effects of Ag-NPs at subinhibitory concentrations, both on planktonic and sessile B. subtilis cells. As determined by 2,7-dichlorofluorescein-diacetate assays, Ag-NPs increase the formation of reactive oxygen species in planktonic cells, but not in sessile cells, suggesting the activation of scavenging systems in biofilms. Consistently, proteomic analysis in B. subtilis Ag-NPs-treated biofilms showed increased production of proteins related to quorum sensing and involved in stress responses and redox sensing. Extracellular polysaccharides production and inorganic phosphate solubilization were also increased, possibly as part of a coordinated response to stress.
  
  
  CONCLUSIONS
  At low concentrations, Ag-NPs killed A. vinelandii and affected cellular processes in planktonic and sessile B. subtilis cells.
  
  
  CONCLUSIONS
  Re-direction of gene expression, linked to selective toxicity, suggests a strong impact of Ag-NPs on soil bacterial communities.
authors.affiliation: Department of Biosciences, Università degli Studi di Milano, Milan, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Gambino
authors.forename: V
authors.initials: V
authors.lastname: Marzano
authors.forename: F
authors.initials: F
authors.lastname: Villa
authors.forename: A
authors.initials: A
authors.lastname: Vitali
authors.forename: C
authors.initials: C
authors.lastname: Vannini
authors.forename: P
authors.initials: P
authors.lastname: Landini
authors.forename: F
authors.initials: F
authors.lastname: Cappitelli
mesh_terms: D001412:Bacillus subtilis / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018441:Biofilms / Q000187:drug effects; D053768:Metal Nanoparticles / Q000633:toxicity*; D010933:Plankton / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D040901:Proteomics; D017382:Reactive Oxygen Species / Q000378:metabolism; D012834:Silver / Q000633:toxicity*
chemical_list: D001426:Bacterial Proteins; D017382:Reactive Oxygen Species; D012834:Silver
keywords: Bacillus; biofilms; proteomics; rhizosphere; stress response