Assessment of the effect of silver nanoparticles on the relevant soil protozoan genus Acanthamoeba

Abstract

Silver nanoparticles (AgNP) are used in a broad range of consumer products and industrial applications. During the regular product life cycle and disposal, AgNP are continuously released into the environment. Hence, the aim of this study was to investigate the potential ecotoxicological effects of AgNP exposure on amoebae. The Acanthamoeba castellanii ATCC 30234 strain and environmental isolate Acanthamoeba strain C5/2, which are both affiliated with genotype T4, were chosen as representatives of ecologically important soil protozoan organisms. The amoebae were exposed to citrate‐stabilized AgNP (30 and 70 nm in size) for 24 h and 96 h at concentrations ranging from 600 µg L−1 to 20 mg L−1. A newly adopted cell culture based microscopic assay was applied to assess the adherence ability of the amoeba trophozoites. The general metabolic activity of Acanthamoeba was determined to be a second independent endpoint by means of intracellular reduction of the redox dye AlamarBlue®. The fate of AgNP within the amoebae and test solutions was visualized by light‐ and transmission electron microscopy (TEM). Both Acanthamoeba strains showed a significant dose‐dependent decrease of adherence ability (p < 0.04) and metabolic activity (p < 0.01) after 96 h of AgNP exposure. The environmental Acanthamoeba strain C5/2 lost both its adherence ability and metabolic activity at lower AgNP concentrations than the type strain, indicating a higher sensitivity to ionic silver. This was confirmed by the application of AgNO3, provoking a higher effect level in strain C5/2. AgNP was visualized intracellularly by transmission electron microscopy within the cytoplasm of Acanthamoeba. This is the first report to show the ecotoxicological effects of short‐term AgNP exposure on the soil protist Acanthamoeba, causing both changes in the adherence ability and metabolic activity of this amoeba. This combined approach may be a powerful tool in the future for predicting potential harmful ecotoxicological effects of AgNP exposure using soil protozoans.

Tannic acid-modified silver nanoparticles as a novel therapeutic agent against Acanthamoeba

“…Regarding studies in Acanthamoeba, AgNPs were tested against the environmental Acanthamoeba strain ATCC 30234. In this case, the obtained results showed significant dose-dependent decrease of adherence ability and metabolic activity after 96 h of exposure (Grün et al 2017). The silver containing solutions were also examined by Willcox et al (2010).…”

Impact of silver nanoparticles (AgNP) on soil microbial community depending on functionalization, concentration, exposure time, and soil texture

“…Further to the soil type and the AgNP functionalization, several studies documented a significant impact of the exposure time on the toxicity of AgNP in soils [16,[32][33][34]. By a statistically significant regression and correlation analysis between silver toxicity and exposure time we recently confirmed loamy soils as a sink for silver nanoparticles and their concomitant silver ions due to ageing processes of the silver species and their slow return to the biological soil system [17].…”

“…An internalization of negatively charged nanoparticles could be occured through nonspecific binding and clustering of the particles on cationic sites on the plasma membrane and subsequent endocytosis or by direct diffusion through the cell membrane [106]. Here, Ag10-COOH could act as a trojan horse: metabolization processes in food vacuoles and lysosomes allow the uncoating of AgNP and enable the direct release of Ag + ions into the cytoplasm causing intracellular damages [32,107].…”

Evaluation of in vitro effect of selected contact lens solutions conjugated with nanoparticles in terms of preventive approach to public health risk generated by Acanthamoeba strains

“…However, despite rapid advance in nanotechnology, only a few studies on the activity of nanoparticles against Acanthamoeba spp. have been previously performed and have shown that the tested nanoparticles are well absorbed by Acanthamoeba trophozoites and decreased their adherence ability and metabolic activity [18,28,29,30]. However, the mechanism of action of AgNPs and AuNPs is still not fully understood.…”