The Antimicrobial Properties of Silver Nanoparticles in Bacillus subtilis Are Mediated by Released Ag+ Ions

Abstract

The superior antimicrobial properties of silver nanoparticles (Ag NPs) are well-documented, but the exact mechanisms underlying Ag-NP microbial toxicity remain the subject of intense debate. Here, we show that Ag-NP concentrations as low as 10 ppm exert significant toxicity against Bacillus subtilis, a beneficial bacterium ubiquitous in the soil. Growth arrest and chromosomal DNA degradation were observed, and flow cytometric quantification of propidium iodide (PI) staining also revealed that Ag-NP concentrations of 25 ppm and above increased membrane permeability. RedoxSensor content analysis and Phag-GFP expression analysis further indicated that reductase activity and cytosolic protein expression decreased in B. subtilis cells treated with 10–50 ppm of Ag NPs. We conducted X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses to directly clarify the valence and fine structure of Ag atoms in B. subtilis cells placed in contact with Ag NPs. The results confirmed the Ag species in Ag NP-treated B. subtilis cells as Ag2O, indicating that Ag-NP toxicity is likely mediated by released Ag+ ions from Ag NPs, which penetrate bacterial cells and are subsequently oxidized intracellularly to Ag2O. These findings provide conclusive evidence for the role of Ag+ ions in Ag-NP microbial toxicity, and suggest that the impact of inappropriately disposed Ag NPs to soil and water ecosystems may warrant further investigation.

Silver nanoparticles reduce the apoptosis induced by tumor necrosis factor-α

“…Several researchers have investigated the effects of AgNPs on the bacterial wall and how AgNPs inhibit bacterial growth [11, 12, and 13]. However, despite these studies, the exact mechanism underlying the anti-inflammatory effect of AgNPs is not clearly understood.…”

Collagen-Nanoparticles Composites for Wound Healing and Infection Control

“…In addition, Hsueh et al reported that a concentration of 10 ppm of Ag NPs exerts significant toxicity against B. subtilis, causing chromosomal DNA (deoxyribonucleic acid) degradation [55].…”

Antimicrobial Activity of Biosynthesized Silver Nanoparticles against E. coli and B. subtilis

“…Previously, heavy metal ions including silver ions were used for their microbial toxicity via reduction of the metal ions or formation of metal sulfides [12]. After the development in AgNPs production, the nanoparticles were used instead of the metal ion owing to their powerful toxicity effect [10,13,14]. The increase in the use of AgNPs in different sectors raised a concern due to their occasional release the environment [9].…”

“…Lots of studies proven that AgNPs penetrate different living cells [13,14]. Therefore, the action of those NPs is inside the cells and not at cellular surface.…”

“…Therefore, the action of those NPs is inside the cells and not at cellular surface. AgNPs exhibit microbial toxicity via the release of Ag+ ions which subsequently penetrate into bacterial cells [14]. McShan et al [15] showed one of the toxicity mechanism which is oxidative stress via reactive oxygen species (ROS) generation, damaging cell membrane and other cell components including DNA, depleting antioxidant molecules (e.g., glutathione), disabling proteins, lowering reductase activity, reducing protein expression and depressing the activity of some membranous enzymes.…”