Protection of Nitrosomonas europaea from Silver Nanoparticle-Induced Inhibition through a Two-Step, Magnesium-Facilitated Mechanism Public Deposited

http://ir.library.oregonstate.edu/concern/undergraduate_thesis_or_projects/xg94hr67w

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  • The inhibitory effects of (Ag⁺) and silver nanoparticles (Ag NP) 3-5 nm in diameter (stabilized with polyvinylpyrrolidone (PVP)) and 20 nm (stabilized with citrate) on nitrification rates of the model ammonia-oxidizing bacteria (AOB) Nitrosomonas europaea were investigated. Experimental solutions contained HEPES buffer and ammonia (NH₃) in the presence and absence of 730 μM Mg²⁺. Ag⁺ showed the most inhibition, and Ag NP-induced inhibition decreased with increasing size. In each case, Mg²⁺ showed protection from nitrification inhibiton. Ag incorporated with the cells was measured by centrifuging experimental fluid, acid-digesting the cell pellet, and measuring via ICP-OES analysis for Ag-content of the digestion. Results indicated that less Ag incorporated with the cells in the presence of Mg²⁺, suggesting that Mg²⁺ inhibits the sorption of Ag to N. europaea. UV-vis spectrophotometric analysis over 25 minutes was used to observe rapid aggregation with minimal dissolution of 20 nm citrate-stabilized Ag NP in media with 730 μM Mg²⁺, and dissolution without aggregation of the Ag NP in media without Mg²⁺. This suggests that Mg²⁺ prevents Ag NP-induced nitrification inhibition of N. europaea via a two-step mechanism: Mg²⁺ induces the aggregation of Ag NP, reducing the release of Ag⁺, and prevents incorporation of Ag to cells.
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