Toxicity of silver nanoparticles in the bacterium Pseudomonas putida

Dong, Feng (2016). Toxicity of silver nanoparticles in the bacterium Pseudomonas putida. University of Birmingham. Ph.D.

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Abstract

This thesis investigated the toxicity of silver nanoparticles (AgNPs) in the bacterium Pseudomonas putida. It is unclear whether the antimicrobial activities of AgNPs are exclusively mediated by the release of silver ions (Ag\(^+\)) or, instead, are due to combined nanoparticle and ions effects. First, a method to measure dissolved Ag in Ag\(^+\)/AgNPs mixtures was developed by combining aggregation of AgNPs with centrifugation. The AgNP stocks were stored in an anoxic environment. Silver nanoparticles underwent different degrees of aggregation and dissolution in Davis minimal medium. Silver ions had stronger toxicity than AgNPs. The minimum inhibitory concentrations of Ag+ and AgNPs for P. putida steadily increased with increasing initial cell densities. Silver nanoparticles acted as a Ag reservoir, releasing Ag\(^+\) to kill bacteria. The toxicity of AgNPs was dominated by dissolved Ag. In an evolution experiment, P. putida populations evolved for ~500 generations under the treatment of Ag\(^+\) or AgNPs. The mutations in the evolved populations stressed by Ag\(^+\) and AgNPs displayed different patterns. The nonsynonymous mutations in AgNP-stressed populations were mostly associated with cell surface proteins, and Ag\(^+\) stress selected for mutations in cytoplasmic proteins linked to metal metabolism, suggesting different toxicity mechanisms of Ag\(^+\) and AgNPs.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):