Defended PhD thesis: Sandra Käosaar

Sandra Käosaar defended her doctoral thesis in Tallinn University of Technology (TUT) on 14 of September 2018.

„Toxicological Profiling of Silver and Copper Oxide Nanoparticles on Saccharomyces cerevisiae BY4741 Wild-Type and Single-gene deletion mutants”

The main aim of the doctoral study was to elucidate Ag and CuO NPs toxicity mechanisms to the yeast Saccharomyces cerevisiae BY4741. Yeast S. cerevisiae was used as a eukaryotic and fungal cell model. Wild-type and its single-gene deletion mutants were comparatively studied. Mutants, sensitive to the ionic and oxidative stress, and cell wall/membrane disturbing agents were applied. To clarify the role of endocytosis in the uptake of NPs by the cells, endocytosis-defective strain (end3D) was used. Use of singe-gene deletion mutants for the profiling of NPs is a novel and promising method in the nanotoxicology studies.

Results showed that the toxicity of Ag and CuO NPs to the yeast cells was mainly caused by the shed of metal ions and can be modulated by the size and surface-coating of NPs and test environment. To our knowledge, that was the first study showing the entry of Ag NPs into the yeast cells by the endocytosis and that the blocking of endocytosis could be one strategy to increase the toxicity of Ag NPs to the yeast cells.

In this work the novel method for assessing the biocidal efficiency of NPs against yeast, bacteria and algae were developed. In this method deionized (DI) water as a non-modulating test environment for the NPs testing is used. The viability of yeast, bacterial and algal cells during 24-h incubation in DI water did not decrease. Possibility to use DI water as a test environment for the microbes can be regarded as a paradigm change, as DI water has been considered so far as not suitable test environment for the microbes due to its hypotonic nature.

The Doctoral thesis was prepared in the Laboratory of Environmental Toxicology, National Institute of Chemical Physics and Biophysics (NICPB).

Supervisor: Dr. Kaja Kasemets (NICPB, senior researcher); Co-supervisors Dr. Anne Kahru (NICPB, leading scientist) and Prof Andres Öpik (TUT).

Opponents: Dr Olga Muter (Latvian University, Riga) and Prof Maia Kivisaar (Tartu University, Estonia).