Differential gene regulation in the Ag nanoparticle and Ag⁺-induced silver stress response inEscherichia coli: A full transcriptomic profile

Abstract

We report the whole-transcriptome response of Escherichia coli bacteria to acute treatment with silver nanoparticles (AgNPs) or silver ions [Ag(I)] as silver nitrate using gene expression microarrays. In total, 188 genes were regulated by both silver treatments, 161 were up-regulated and 27 were down-regulated. Significant regulation was observed for heat shock response genes in line with protein denaturation associated with protein structure vulnerability indicating Ag(I)-labile -SH bonds. Disruption to iron-sulphur clusters led to the positive regulation of iron-sulphur assembly systems and the expression of genes for iron and sulphate homeostasis. Further, Ag ions induced a redox stress response associated with large (>600-fold) up-regulation of the E. coli soxS transcriptional regulator gene. Ag(I) is isoelectronic with Cu(I), and genes associated with copper homeostasis were positively regulated indicating Ag(I)-activation of copper signalling. Differential gene expression was observed for the silver nitrate and AgNP silver delivery. Nanoparticle delivery of Ag(I) induced the differential regulation of 379 genes; 309 genes were uniquely regulated by silver nanoparticles and 70 genes were uniquely regulated by silver nitrate. The differential silver nanoparticle-silver nitrate response indicates that the toxic effect of labile Ag(I) in the system depends upon the mechanism of delivery to the target cell.

Repeated dose (28-day) administration of silver nanoparticles of varied size and coating does not significantly alter the indigenous murine gut microbiome

“…Thus, despite having in vitro antimicrobial properties (Morrill et al, 2013, McQuillan et al, 2012, McQuillan and Shaw, 2014, Ivask et al, 2014), ingested AgNPs do not appear to have a similar effect on the gut microbiome as do broad-spectrum antibiotics (Theriot et al, 2014, Theriot et al, 2011, Bassis et al, 2014). This finding is significant in assessing the potential for antimicrobial effects of ingested silver nanoparticles at exposure levels likely to be encountered in consumer products and dietary additives.…”

“…Most in vitro experimental evidence suggests that dissolution and local silver ion concentration play a significant role in the antimicrobial activity of AgNP (McQuillan et al, 2012, McQuillan and Shaw, 2014, Behra et al, 2013), although some aspects are not entirely explained by Ag ion availability (McQuillan and Shaw, 2014, Ivask et al, 2014). Assuming that antimicrobial effects of silver are dependent on direct interaction with gut microbes (Volker et al, 2013, Behra et al, 2013), particles present in higher luminal concentrations in the distal gut, which is the site of maximal bacterial concentration, may be more likely to have antimicrobial effects.…”

ZnO Nanoparticles Impose a Panmetabolic Toxic Effect Along with Strong Necrosis, Inducing Activation of the Envelope Stress Response in Salmonella enterica Serovar Enteritidis

“…Intriguingly, all housekeeping proteins (enzymes) of Salmonella serovar Enteritidis with altered expression were downregulated (Table 2). Recently, McQuillan and Shaw (26), using the whole-transcriptome gene expression approach in order to capture the global genetic response of Escherichia coli to Ag nanoparticles, showed that various genes encoding enzymes of the central metabolic pathways were upregulated, indicating that Ag NPs could not affect major enzymes involved in carbohydrate transport, sugar phosphotransferase systems, the galactitol metabolic process, and nitrogen fixation. In sharp contrast to the findings for Ag NPs, our study showed that ZnO NPs affected a wide range of key enzymes involved in numerous central metabolic pathways, clearly imposing a panmetabolic toxic effect on this prokaryotic organism (Fig.…”

Synthesis and Complete Antimicrobial Characterization of CEOBACTER, an Ag-Based Nanocomposite

“…Controversy exists regarding the possible mechanism of action of silver nanoparticles on microorganisms [8,18,35,42–44]. In particular, if the bactericidal effect of silver nanoparticles is due to direct contact of the nanomaterial with bacteria, or by the release of ions which alter the membrane and cause cell death, or by a combination of both effects.…”