Antimicrobial Efficacy and Mechanisms of Silver Nanoparticles Against Phanerochaete Chrysosporium in the Presence of Common Electrolytes and Humic Acid

In this study, influences of cations (Na, K, Ca, and Mg), anions (NO, Cl, and SO), and humic acid (HA) on the antimicrobial efficacy of silver nanoparticles (AgNPs)/Ag against Phanerochaete chrysosporium were investigated by observing cell viability and total Ag uptake. K enhanced the antimicrobial toxicity of AgNPs on P. chrysosporium, while divalent cations decreased the toxicity considerably, with preference of Ca over Mg. Impact caused by a combination of monovalent and divalent electrolytes was mainly controlled by divalent cations. Compared to AgNPs, however, Ag with the same total Ag content exhibited stronger antimicrobial efficacy towards P. chrysosporium, regardless of the type of electrolytes. Furthermore, HA addition induced greater microbial activity under AgNP stress, possibly originating from stronger affinity of AgNPs over Ag to organic matters. The obtained results suggested that antimicrobial efficacy of AgNPs was closely related to water chemistry: addition of divalent electrolytes and HA reduced the opportunities directly for AgNP contact and interaction with cells through formation of aggregates, complexes, and surface coatings, leading to significant toxicity reduction; however, in monovalent electrolytes, the dominating mode of action of AgNPs could be toxic effects of the released Ag on microorganisms due to nanoparticle dissolution.