The rapidly increasing use of silver nanoparticles (silver NPs) nowadays may have led to contamination of silver NPs into environments, generating adverse effects on organisms dwelling in polluted ecosystems. Although the antibacterial property of these particles is widely accepted, their effects on unicellular eukaryotic microorganisms are not frequently reported. The objective of this study was therefore to assess toxicity of the silver NP prepared in a colloidal solution form to three species of ciliates, namely Bresslauides sp., Paramecium sp., and Telotrochidium sp. Morphological response at cellular level, growth rate, and generation time of each ciliate as well as concentrations of the silver NP that produce mortality in 50% of the treated cells (LC₅₀) after 24 h incubation were investigated. The results indicated that Paramecium sp. showed the highest sensitivity to the silver NP, followed by Bresslauides sp. and Telotrochidium sp. with the LC₅₀ values of 0.753, 0.978, and 1.741 mg/l, respectively. In addition, the three examined ciliates treated with the silver NP demonstrated slower swimming locomotion and exhibited several morphological alterations, including formation of intracellular vacuoles, plasma membrane blebbing, cellular deformities, and subsequent disintegration. Furthermore, the silver NP was observed to decrease growth rates and to double generation times of all tested ciliates. The highest sensibility of Paramecium sp. to the silver NP suggests the feasibility of using this isolate as a biological assessor for detecting possible contaminations of the nanoparticle in aquatic environments.
