Castles fall from inside: Evidence for dominant internal photo-catalytic mechanisms during treatment of Saccharomyces cerevisiae by photo-Fenton at near-neutral pH

In this work, the antimicrobial effects of the photo-Fenton process on yeast cells were tested (Saccharomyces cerevisiae), an essential eukaryotic unicellular model of living cells. Near-neutral pH was used in all studies, while iron sulfate and iron citrate were evaluated as iron sources during S. cerevisiae photo Fenton inactivation under simulated solar light (hv/H2O2/Fe). The following indicators were monitored to decrypt the mechanism of yeast inactivation by neutral photo-Fenton process: cell viability by flow cytometry, damage at DNA level, as well as intracellular and extracellular proteins, assessed by gel electrophoresis. A significant loss of cultivability was monitored through the application of all the different photo-Fenton systems, attributed to the oxidative stresses applied. The mechanisms involved were the homogeneous action of dissolved iron and the heterogeneous action mode of iron oxides. The DNA and protein analyses indicated drastic intracellular damages, while external macromolecules (cell wall and membrane proteins) showed limited degradation. This marked internal photocatalytic processes as the main inactivation mechanism in S. cerevisiae. Different pathways are proposed, forming a general process of inactivation by the near-neutral photo-Fenton systems. (C) 2015 Elsevier B.V. All rights reserved.