Two non-exclusive strategies employed to protect Torulopsis glabrata against hyperosmotic stress

Several recent reports described an apoptosis-like programmed cell death (PCD) process in yeast in response to different environmental challenges. In this study, hyperosmotic stress caused by high NaCl concentration in culture medium induced cell death in the haploid yeast Torulopsis glabrata. Propidium iodide (PI) and PI/rhodamine-123 (Rh123) dual staining with flow cytometry showed that high salinity decreased intact cells by 16.5 %, increased necrotic cells by nearly twofold, and altered fermentative parameters appreciably. Morphological and biochemical indicators of apoptosis were apparent, specifically a decrease in mitochondrial membrane potential (∆Ψm), translocation of phosphatidylserine (PS) from the inner to the outer side of the plasma membrane, generation of reactive oxygen species (ROS), and involvement of caspase all while plasma membrane integrity was maintained. Additionally, it was found that overexpression of YCA1 drastically stimulated cell death, indicating that activation of metacaspase might lead to cell death. However, T. glabrata growth under hyperosmotic stress was enhanced when FIS1, HOG1, and GPD2 were overexpressed, or when exogenous proline or glutathione (GSH) were added into the cultures, both of which could repress caspase-3 activity. Thus, in these concrete cases of overexpression of anti-apoptotic or anti-necrotic factors and pharmacological manipulations, it decreased T. glabrata cell death that might help to achieve higher fermentative efficiency.