Silver Sink Effect of Humic Acid on Bacterial Surface Colonization in the Presence of Silver Ions and Nanoparticles

TitleSilver Sink Effect of Humic Acid on Bacterial Surface Colonization in the Presence of Silver Ions and Nanoparticles
Publication TypeJournal Article
Year of Publication2017
AuthorsBertuccio, AJ, Tilton, RD
JournalEnviron Sci TechnolEnviron Sci Technol
Volume51
Pagination1754-1763
Date Published02/2017
ISBN Number1520-5851 (Electronic) 0013-936X (Linking)
Accession Number27997146
Abstract

Silver nanoparticles (AgNPs) released from consumer products may enter the environment and possibly harm microbial communities. Prior research showed that surface-adherent AgNPs inhibit bacterial surface colonization, a precursor to biofilm formation, only when planktonic bacterial inoculum concentrations are less than a threshold level ( Wirth and co-workers, J. Colloid Interface Sci. 2016 , 467 , 17 - 27 ). This inoculum effect is due to a decrease in free silver ion concentration associated with sublethal binding to bacteria. Natural organic matter can be an additional silver sink in environmental systems. Using Pseudomonas fluorescens as a model biofilm-forming bacterium, we find significant increases in minimum bactericidal concentrations for AgNP suspensions and Ag+ in solution when adding humic acid (HA) to bacterial suspensions. When HA is present, planktonic bacteria survive and colonize AgNP-laden glass surfaces at lower bacterial inoculum concentrations than were needed for survival and colonization in its absence. This occurs despite the observed tendency of HA to inhibit colonization on bare glass surfaces when silver is absent. Results are interpreted through equilibrium Ag+ binding isotherms to HA and suspended bacteria. These results indicate that silver ion sinks may lessen AgNP impacts on natural microbial ecology relative to the disruption observed in pristine laboratory conditions.