Unravelling the Molecular Responses of the Yeast Schwanniomyces etchellsii to Hyperosmotic Stress in Seawater Medium Using Omic Approaches

<i>Schwanniomyces etchellsii</i> is an unconventional, halotolerant microorganism. Like some other yeasts, it can efficiently perform various biocatalytic transformations of organic compounds in seawater more effectively than in freshwater. In seawater, conversion rates are higher, by-product production is minimized, greater substrate loading is possible, and cells can be recycled for further use. To identify the molecular features that explain this behavior, comparative proteomic and lipidomic studies were conducted on cells grown in seawater and freshwater at various growth stages. The results showed higher expression of proteins involved in the stress response, such as glycerol-3-phosphate dehydrogenase, the glycerol transporter Stl1 and the P-type ATPase sodium pump Ena1, and several phospholipid biosynthesis proteins, including inositol-3-phosphate synthase and phosphatidate cytidylyltransferase, in seawater. Changes in metabolic enzymes and other proteins involved in responding to stimuli were also observed between the two conditions. Overall, cells grown in a freshwater medium exhibited higher levels of enzymes involved in biosynthetic processes. Differences in lipid profiles were also observed between cells grown in the two media. Higher levels of monoacyl and diacylglycerols were found in seawater, while higher levels of phospholipids containing serine and ethanolamine were found in freshwater. Consistent with more permeable membranes, cells grown in seawater exhibited lower levels of ergosterol.