Synchrotron FTIR microspectroscopy of the yeast Saccharomyces cerevisiae after exposure to plasma-deposited nanosilver-containing coating

International audienceThe present work was focused on elucidating changes in the model yeast Saccharomyces cerevisiae (cell composition, ultrastructure) after exposure to antimicrobial plasma-mediated nanocomposite films. In order to achieve this, a nanosilver-containing coating was deposited onto stainless steel using radiofrequency HMDSO plasma deposition, combined with simultaneous silver sputtering. X-ray photoelectron spectroscopy (XPS) confirmed the presence of silver nanoparticles embedded in an organo-silicon matrix. In addition, scanning electron microscopy (SEM) demonstrated the nanoparticle-based morphology of the deposited layer. The antifungal properties towards S. cerevisiae were established, since a 1.4 log reduction in viable counts was observed after a 24-h adhesion compared to control conditions with the matrix alone. Differences in cell composition after exposure to the nanosilver was assessed for the protein region using, for the first time, synchrotron Fourier-transform infrared (FTIR) microspectroscopy of single S. cerevisiae cells, through in situ mapping with sub-cellular spatial resolution. IR spectrum of yeast cells recovered after a 24-h adhesion to the nanosilver-containing coating revealed a significant downshift (20 cm −1) of the amide I peak at 1655 cm −1 , compared to freshly harvested cells. This lower band position, corresponding to a loss in α-helix structures, is indicative of the disordered secondary structures of proteins, due to the transition between active and inactive conformations under nanosilver-induced stress conditions. No significant effect on the nucleic acid region was detected. The inhibitory action of silver was targeted against both cell wall and intracellular proteins such as enzymes. Transmission electron microscopy (TEM) observations of the yeastultrastructure confirmed serious morphological and structural damages. A homogeneous protein-binding distribution of nanosilver all over the cell was assumed, since the presence of electron-dense silver clusters was detected not only on the cell surface but also within the cell. For control experiments with the organosilicon matrix alone, no antimicrobial effect was observed, which was consistent with synchrotron FTIR results and TEM observations