title: Impacts of silver nanoparticle coating on the nitrification potential of Nitrosomonas europaea.
abstract: Silver nanoparticles (AgNPs) are increasingly used as bacteriostatic agents to prevent microbial growth. AgNPs are manufactured with a variety of coatings, and their potential impacts on wastewater treatment in general are poorly understood. In the present study, Nitrosomonas europaea, a model ammonia oxidizing bacterium, was exposed to AgNPs with citrate, gum arabic (GA), and polyvinylpyrrolidone (PVP). GA and citrate AgNPs inhibited nitrification most strongly (67.9 ± 3.6% and 91.4 ± 0.2%, respectively at 2 ppm). Our data indicate that Ag(+) dissolution and colloid stability of AgNPs were the main factors in AgNP toxicity. In general, low amounts of dissolved Ag initially caused a post-transcriptional interruption of membrane-bound nitrifying enzyme function, reducing nitrification by 10% or more. A further increase in dissolved Ag resulted in heavy metal stress response (e.g., merA up-regulation) and ultimately led to membrane disruption. The highest effect on membrane disruption was observed for citrate AgNPs (64 ± 11% membranes compromised at 2 ppm), which had high colloidal stability. This study demonstrates that coating plays a very important role in determining Ag dissolution and ultimately toxicity to nitrifiers. More research is needed to characterize these parameters in complex growth media such as wastewater.
authors.affiliation: Department of Civil and Environmental Engineering, Duke University, Box 90287, Durham, North Carolina 27708, United States.
authors.forename: Christina L
authors.initials: CL
authors.lastname: Arnaout
authors.forename: Claudia K
authors.initials: CK
authors.lastname: Gunsch
mesh_terms: D002462:Cell Membrane / Q000187:drug effects / Q000648:ultrastructure; D019343:Citric Acid / Q000737:chemistry*; D003545:Cysteine / Q000494:pharmacology; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D020868:Gene Silencing / Q000187:drug effects; D005798:Genes, Bacterial / Q000235:genetics; D006170:Gum Arabic / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D050296:Microbial Viability / Q000187:drug effects; D058465:Nitrification / Q000187:drug effects*; D009573:Nitrites / Q000032:analysis; D043370:Nitrosomonas europaea / Q000166:cytology / Q000187:drug effects* / Q000235:genetics / Q000648:ultrastructure; D011205:Povidone / Q000737:chemistry*; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012834:Silver / Q000494:pharmacology*; D012995:Solubility / Q000187:drug effects
chemical_list: D009573:Nitrites; D012336:RNA, Ribosomal, 16S; D019343:Citric Acid; D012834:Silver; D006170:Gum Arabic; D011205:Povidone; D003545:Cysteine