Toxicity of differently sized and charged silver nanoparticles to yeast Saccharomyces cerevisiae BY4741: a nano-biointeraction perspective

Abstract

In the current study, we evaluated the modulatory effects of size and surface coating/charge of AgNPs on their toxicity to a unicellular yeast Saccharomyces cerevisiae BY4741 – a fungal model. For that, the toxicity of a set of 10 and 80 nm citrate-coated (negatively charged) and branched polyethylenimine (bPEI) coated (positively charged) AgNPs was evaluated in parallel with AgNO₃ as ionic control. Yeast cells were exposed to different concentrations of studied compounds in deionized water for 24 h at 30 °C and evaluated for the viability by the post-exposure colony-forming ability. Particle-cell interactions were assessed by SEM, TEM and confocal laser scanning microscopy (CLSM) in the reflection mode. AgNPs toxicity to yeast was size and charge-dependent: 24-h IC₅₀ values ranged from 0.04 (10nAg-bPEI) up to 8.3 mg Ag/L (80nAg-Cit). 10 nm AgNPs were 5–27 times more toxic than 80 nm AgNPs and bPEI-AgNPs 8–44 times more toxic than citrate-AgNPs. SEM and TEM visualization showed that bPEI-AgNPs but not citrate-AgNPs adsorbed onto the yeast cell’s surface. However, according to CLSM all the studied AgNPs, whatever the size and coating, ended up within the yeast cell. Toxicity of citrate-AgNPs was largely explained by the dissolved Ag ions but the bPEI-AgNPs showed mainly particle-driven effects leading to the cellular internalization and/or to more pronounced dissolution of AgNPs in the close vicinity of the cell wall. Therefore, the size, and especially the coating/charge of AgNPs can be efficiently used for the design of new more efficient antifungals.

Keywords:

• Silver nanoparticles
• toxicity
• cell structure
• confocal and electron microscopy

Acknowledgments

The authors thank Dr. Nadia Santo (University of Milano, Italy) for the TEM-ESI analyses and Dr. Anne Kahru (National Institute of the Chemical Physics and Biophysics, Estonia) for her comments on the manuscript.

Disclosure statement

The authors declare no conflict of interest.

Additional information

Funding

This work was supported by the Estonian Research Council grants IUT 23-5 and ETF9001, Fondazione Cariplo grant to the project OverNanoTox (2013–0987), the ERDF project ‘Centre of Technologies and Investigations of Nanomaterials (NAMUR+)’, project number 2014-2020.4.01.16-0123 and ‘Center of Excellence’ project TK134 ‘Emerging orders in quantum and nanomaterials (1.08.2015–31.08.2023)’, and EU COST Action ES1205.